Finn Lennartsson1,2, Bo Nordell1, Olof Flodmark2
1Karolinska University Hospital, Dept of Medical Physics, Stockholm, Sweden; 2Karolinska University Hospital, Dept of Neuroradiology, Stockholm, Sweden
The T1-relaxation process is a well-known issue in diffusion-weighted magnetic resonance imaging (DWI). A typical diffusion-tensor imaging (DTI) scheme collects first the S0:s followed by gradient directions: S01,..., S0m S(r1),..., S(rn). The T1-weighting among the initial S0:s is not homogenous, giving an erroneously high baseline (mean of S0:s), which results in an overestimation of the tensor elements. T1-relaxation effects in the initial volumes of a DTI experiment have an impact on the estimation of a tensor-derived ADC-map, and the same effect is expected for non-tensor models. The effect is especially prominent in tissues with long T1 like CSF, where a overestimation of ADC is expected.
1555. Linking the Individual EEG Alpha Frequency to the Brain’s Fibers
Andrea Federspiel1, Thomas Koenig1, Thomas Dierks1, Kay Jann1
1Psychiatric Neurophysiology, University Hospital of Psychiatry, Bern 60, Switzerland
The Individual EEG alpha frequency (IAF) correlates with subjects’ performance in cognitive tasks. However, the functional networks and structural substrate underlying the inter-individual differences in IAF are largely unknown. Here we investigated on structural correlates in terms of white matter fiber trakts that are related to the subjects’ IAFs. We observed dedicated structure-function correlates in the cingulum involved in the DMN and in the arcuate fascicle associated with the left-WMN. Subjects with higher IAF tend to be faster and perform better in various cognitive tasks. Therefore, our observations suggest that structural connectivity among task relevant areas affects processing capacity.
Hiroshi Kawaguchi1, Takayuki Obata1, Harumasa Takano2, Miho Ota2, Yoshihide Akine2, Hiroshi Ito2, Hiroo Ikehira1, Iwao Kanno1, Tetsuya Suhara2
1Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan; 2Department of Molecular Neuroimaging, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
Positron emission tomography with L-[β- 11C]DOPA and diffusion tensor imaging were measured on the same group of volunteers to assess the relationship between dopamine synthesis and cell-level structure in the striate body. There was a negative correlation between dopamine synthesis ratio and mean diffusivity in the left striate body, which indicates that the more water motion is restricted, the more dopamine is synthesized in the left striate body. Assuming that water motion is related to celluarity, the result suggests dopamine synthesis may depend on the density of dopaminergic neurons.
1557. The Influence of the Registration on Voxel-Based Statistics of Fractional Anisotropy Images: Using Detected White Matter Degenerations Associated with Juvenile Myoclonic Epilepsy as a Gold Standard
Siawoosh Mohammadi1, Volkmar H. Glauche2, Simon S. Keller1, Michael Deppe1
1Department of Neurology, University of Muenster, Muenster, NRW, Germany; 2Department of Neurology, University of Freiburg, Freiburg, Germany
Recent developments have enabled automated voxel-based statistical (VBS) analyses of fractional anisotropy (FA) images (FA-VBS). However, due to the lack of a gold standard the question, which spatial normalization is best for FA-VBS, is still not answered. To assess the influence of the registration on the FA-VBS results, we investigate the white matter (WM) of juvenile myoclonic epilepsy patients with a-priori known damage that correlates with the frequency of generalized tonic-clonic seizures (GTCS). To perform the registration we used the SPM-normalization toolbox. We showed that the correlation between GTCS and WM-damage was best detected if multi-contrast, iterative registration was used.
1558. Different Higher-Order Auditory Processing Tasks Show Differing Correlations with White Matter Microstructure in Normal-Hearing Children
Vincent Jerome Schmithorst1, Scott Kerry Holland1, Elena Plante2
1Radiology, Children's Hospital Medical Center, Cincinnati, OH, United States; 2Speech, Language, & Hearing Sciences, University of Arizona, Tucson, AZ, United States
A diffusion tensor imaging (DTI) study was conducted in a cohort of normal-hearing children ages 9-11 investigating correlations of white matter microstructure with higher-order auditory processing tasks often used to diagnose auditory processing disorder (APD) in children. The more difficult tasks showed negative correlations of fractional anisotropy (FA) in the corticospinal tract with task performance, while the easiest task showed a positive correlation. Positive correlations of FA with task performance were also seen in white matter adjoining prefrontal and occipital areas for some tasks. Results support a dual-stream (dorsal and ventral) model of auditory comprehension.
1559. The Effects of HIV and Hepatitis C Infection on Diffusion Tensor Imaging Measures
Huiling Peng1, Jewell Thomas1, Joseph Mettenburg2, Avi Snyder1, Tammie Benzinger2, David Clifford1, Robert Paul3, Beau Ances4
1Neurology, Washington University in St. Louis, St. Louis, MO, United States; 2Radiology, Washington University in St. Louis, St. Louis, MO, United States; 3Psychology, University of Missouri St. Louis, St. Louis, MO, United States; 4Neurology, Washington University in St. Louis, St. Louis, MO , United States
Hepatitis C virus (HCV) is a frequent co-infection with HIV. Both affect brain function raising the possibility of synergistic interactions. We investigate the relationship between neurological function and white matter integrity using DTI in mono (HIV+) (n=15) vs. co-infected (HIV+/HCV+) (n=13) participants. Regions-of-interest corresponding to the cingulum and genu of the corpus callosum were selected. Co-infected participants were more impaired than mono-infected HIV+ subjects on neuropsychological testing but no significant differences were seen for DTI values. The combination of HIV and HCV co-infection affected measures within the brief neurocognitive screening but not structural neuroimaging measures.
1560. Fractional Anisotropy in Various White and Gray Matter Regions in Adulthood. Dependence on Age and Comparison of Two DTI Sequences
Jiøí Keller1,2, Aaron Michael Rulseh1, Michael Syka1, Josef Vymazal1
1Nemocnice Na Homolce, Prague, Czech Republic; 23rd Faculty of Medicine, Charles University in Prague, Prague, Czech Republic
We measured FA in white and gray matter regions using two different DTI sequences (12 and 30 directions) in 23 healthy adult volunteers A number of white and gray matter regions were selected including basal ganglia and corpus callosum. The gray matter results were correlated with expected iron concentration. We detected a significant correlation between age and FA for both DTI sequences in the rostrum of the corpus callosum, anterior internal capsule and the pyramidal tract. A significant difference in FA between DTI sequences was detected in the basal ganglia where correlation between iron amount and FA was found.
1561. Optimized Diffusion MRI Protocols for Estimating Axon Diameter with Known Fibre Orientation
Torben Schneider1, Henrik Lundell2,3, Tim B. Dyrby2, Daniel C. Alexander4, Claudia Angela Michela Wheeler-Kingshott1
1NMR Unit, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom; 2Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark; 3Department of Excercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark; 4Centre for Medical Image Computing, Department of Computer Science, UCL, London, United Kingdom
We present a method that optimizes diffusion MRI protocols to be sensitive to axon diameter and axonal density in white matter structures with known single fibre direction. Computer simulations clearly show that our method improves accuracy of measurements compared to protocols independent of fibre orientation, especially when signal-to-noise-ratio is low. Furthemore, we generate indices of axon diameter and density from a fixated monkey spinal cord and are able to discriminate anatomically different white matter regions.
1562. In Vivo Mapping of Relative Axonal Diameter of Human Corpus Callosum Using Q-Planar Magnetic Resonance Imaging
Jun-Cheng Weng1,2, Wen-Yih Iascc Tseng1,3
1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan; 3Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan
The corpus callosum (CC) is the main fiber tract connecting bilateral cerebral hemispheres, serving information transfer and processing in various cognitive functions. In view of the topographically-specific relation between callosal regions and the connected cortical regions, several partitioning approaches have been proposed to allow separate analysis of different callosal sectors. Vertical partitions are commonly used which subdivide the CC into five regions based on fractions of its maximal anterior-posterior length as proposed by Wiltelson. These regions might be affected differently in the development of disease, and their structural parameters such as size and shape might associate with cognitive or functional tests involved in different modes of interhemispheric interactions. This study proposed a novel technique, q-planar imaging (QPI) to map the relative axonal diameters of CC in normal human brain. It was based on the Fourier relationship between probability density function (PDF) of the water molecular diffusion and sampled diffusion attenuated images in the space of spatial modulation, dubbed q-space. It provided MR images in which physical parameters of water diffusion such as the mean displacement and the probability at zero displacement of water molecules were used as image contrast. Our results demonstrated that QPI produced reasonable distribution of relative axonal diameters of CC in normal human brain.
1563. The Extracellular Diffusion Weighted Signal Predicts Axon Diameter Distribution Parameters
Hubert Martinus Fonteijn1, Matt G. Hall1, Daniel C. Alexander1
1Computer Science, Centre for Medical Image Computing, London, United Kingdom
The estimation of axon diameter distribution parameters remains a big challenge for diffusion-weighted imaging. Generally, only intracellular diffusion is considered to be influenced by axon diameter. Extracellular diffusion on the other hand is considered to be approximately Gaussian in the long diffusion time limit and to be independent of axon diameter. In this abstract, we perform Monte Carlo simulations of diffusion in the extracellular compartment for a wide range of diffusion times and we construct a non-parametric model of extracellular diffusion using Gaussian Process Regression. We then show that axon diameter distribution parameters can be estimated from this model.
1564. Polynomial Models of the Spatial Variation of Axon Radius in White Matter
Gemma Louise Morgan1, Rexford D. Newbould2, Brandon Whitcher2, Daniel C. Alexander1
1Centre for Medical Image Computing, University College London, London, United Kingdom; 2Clinical Imaging Centre, GlaxoSmithKline, London, United Kingdom
Axon radius r is a potentially useful clinical biomarker that can be derived from diffusion weighted imaging. However its estimation in a clinical setting is hampered by poor signal-to-noise ratio and limited sensitivity to small axon radii at low gradient strengths. In this study we introduce a technique for estimating a mean radius index ρ that exploits the spatial coherence of axon radii across the corpus callosum. Specifically, we fit a polynomial model of the spatial variation of ρ. This significantly reduces the total number of parameters to estimate and provides sensitivity to axon radius, even at typical clinical gradient strengths.
1565. Can AxCaliber Be Extended to Estimate Axonal Radius and Orientation at the Same Time?
Jaime E. Cisternas1
1Engineering and Applied Sciences, Universidad de los Andes, Santiago, RM, Chile
Diffusion tensor MRI provides biomarkers that have been shown to indicate microstructural features in the brain and other organs. These biomarkers, even though contain information about development, ageing and disease progression, lack specificity and don't give direct measures of axon density and radius. Several approaches, within the framework of diffusion weighted MR, have been proposed to extract radii, assuming previous knowledge of the orientation of the axons. In this work we extend AxCaliber, to measure axon diameter distribution along multiple orientations, and use numerical simulations to evaluate the capacity of the model to estimate radius and orientation reliably under the presence of noise.
1566. The Effect of Beading and Permeable Axons on Water Diffusion Properties: A Monte Carlo Simulation of Axonal Degeneration and Its Effect on DTI and Q-Space Contrasts
Jonathan Andrew David Farrell1,2, Bennett A. Landman3,4, Jiangyang Zhang1, Seth A. Smith5,6, Daniel S. Reich1,7, Peter A. Calabresi8, Peter C.M. van Zijl1,2
1Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 2Kennedy Krieger Institute, F.M. Kirby Research Center for Functional Brain Imaging, Baltimore, MD, United States; 3Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 4Electrical Engineering, Vanderbilt University, Nashville, TN, United States; 5Dept. of Radiology, Vanderbilt University, Nashville, TN, United States; 6Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; 7Neuroimmunology Branch (NINDS), National Institutes of Health, Bethesda, MD, United States; 8Dept. of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
Axonal injury can produce constrictions and enlargements (“beading”) of axon membranes and increase their permeability. Here we investigate the effect of these morphological parameters on diffusion properties measured with diffusion tensor and q-space imaging. Degenerating axons are modeled as the union of cylinders and spheres of varying radii. Using Monte Carlo simulations, with intra- and extra-cellular compartments, we show that beading and increased permeability can act in concert to produce increased perpendicular diffusion. However, while parallel diffusion is decreased by beading, non-Gaussian behavior is mitigated by increased permeability. This study may aid the development of contrasts specific for axonal injury.
Håkan Hagslätt1,2, Markus Nilsson3, Henrik Hansson3, Jimmy Lätt1,3, Danielle van Westen1,2
1Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; 2Department of Diagnostic Radiology, Lund University Hospital, Lund, Sweden; 3Department of Medical Radiation Physics, Lund University, Lund, Sweden
Axons in fibre tracts may be non-straight and have an undulating, approximately sinusoidal course. It is known that axonal undulations are present in the peripheral nervous system and in some parts of the central nervous system that are subjected to strain during locomotion, for instance, the optic nerve. These undulations might affect parameters estimated using diffusion MRI, such as the fractional anisotropy. Furthermore, measurements attempting to estimate the axonal sizes might be biast towards an overestimated axonal size when undulations are present.
1568. A New Approach to Structural Integrity Assessment Based on Axial and Radial Diffusivities.
Claudia Angela Michela Wheeler-Kingshott1, Olga Ciccarelli2, Torben Schneider1, Daniel C. Alexander3, Mara Cercignani4
1NMR Unit, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom; 2NMR Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, London, United Kingdom; 3Dept. Computer Science, UCL, Centre for Medical Image Computing, London, United Kingdom; 4Neuroimaging Laboratory, Fondazione Santa Lucia, Rome, Italy
A new definition of projected-axial (dp-ax) and radial (dp-rad) diffusivities in standard space has been tested in multiple sclerosis and healthy subjects using VBM. For each subject, dp-ax and dp-rad are defined as the components of the diffusion tensors (DTs) along the most probable direction of healthy tracts as defined by the eigenvectors of a “super-DT” dataset in standard space (calculated as the average of the DTs of a reference group of healthy subjects). The results show that in a patient with moderate disability there are areas of reduced dp-ax not revealed by the principal eigenvalue of the DT.
1569. White Matter Model for Diffusional Kurtosis Imaging
Els Fieremans1, Jens H. Jensen1, Ali Tabesh1, Caixia Hu1,2, Joseph A. Helpern1,2
1Radiology, New York University School of Medicine, New York, United States; 2Center for Advanced Brain Imaging, Nathan S. Kline Institute, Orangeburg, NY, United States
We develop an idealized two-compartment diffusion model of white matter suitable for analysis with diffusional kurtosis imaging (DKI). The standard DKI metrics are used to derive the extracellular and axonal bare diffusion coefficients, the axonal water fraction (AWF), and tortuosity of the extra-axonal geometry, both providing information related to axonal and myelin density. Values for these parameters obtained for a healthy volunteer agree well with those of prior studies. Since a DKI dataset is acquired within a few minutes, this approach may allow for the clinical assessment of myelin associated neuropathologies, such as multiple sclerosis and Alzheimer’s disease.
1570. A Mechanism for Exchange Between Intraaxonal and Extracellular Water: Permeable Nodes of Ranvier
Markus Nilsson1, Håkan Hagslätt2,3, Danielle van Westen2,3, Ronnie Wirestam1, Freddy Ståhlberg1,3, Jimmy Lätt1,2
1Department of Medical Radiation Physics, Lund University, Lund, Sweden; 2Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; 3Department of Diagnostic Radiology, Lund University, Lund, Sweden
The axonal water exchange time was investigated in Monte Carlo simulations using impermeable myelin sheaths, but permeable nodes of Ranvier. The results showed that axonal exchange times on the sub-second were possible for short and intermediate internodal lengths (i.e. length of the myelin sheath) and high nodal permeability. This is of importance for high b-value diffusion MRI when measured with different diffusion times.
1571. Renormalization Group Method: Influence of Packing Density of Axons on Diffusivity in Enhanced Basser-Sen Model of the Brain White Matter
Oleg P. Posnansky1, N. J. Shah2,3
1Institute of Neuroscience and Medicine - 4, Medical Imaging Physics, Forschungszentrum Juelich, GmbH, 52425 Juelich, Germany; 2Institute of Neuroscience and Medicine - 4, Medical Imaging Physics , Forschungszentrum Juelich, GmbH , 52425 Juelich, Germany; 3Deparment of Neurology, Faculty of Medicine, RWTH Aachen University, 52074 Aachen, Germany
Diffusion weighted MRI is sensitive to tissue architecture on a micrometer scale. Determining whether it is possible to infer the specific mechanisms that underlie changes in the DW-MRI could lead to new diffusion contrasts specific to particular white-matter degeneration processes. We have developed a renormalization-group method in order to explore the effects of a large range of microparameters on apparent-diffusion and applied it to different kind of brain tissue tessellations. Our approach takes the influence of disorder into the consideration and it allows quantitative investigation of the sensitivity of apparent-diffusion to the variations of the dominant set of microparameters.
1572. Observation of Anisotropy at Different Length Scales in Optic and Sciatic Nerve Speciments
Evren Ozarslan1, N Shemesh2, Y Cohen2, Peter J. Basser
1NIH, Bethesda, MD, United States; 2Tel Aviv University
Double-PFG MR is a promising method to assess restriction induced anisotropy at different length scales enabling the extraction of information such as compartment size, shape, and orientation distribution function. In this work, we present the simultaneous characterization of the axon diameter and the dispersion in the orientation of the axons in excised optic and sciatic nerve specimens. Assuming a von Mises distribution for the orientation distribution function enabled the characterization of the dispersion of fiber orientations via the estimation of only one additional parameter.
1573. Random Walks in the Model Brain Tissue: Monte Carlo Simulations and Implications for Diffusion Imaging
Farida Grinberg1, Yuliya Kupriyanova1, Ana-Maria Oros-Peusquens1, N Jon Shah1,2
1Medical Imaging Physics, Institute of Neuroscience and Medicine 4, Forschungszentrum Juelich GmbH, Juelich, Germany; 2Department of Neurology, Faculty of Medicine, RWTH Aachen University, Aachen, Germany
The propagation of water molecules in the brain and the corresponding NMR response are affected by many factors such as compartmentalization, restrictions, and anisotropy imposed by the cellular microstructure. In addition, interfacial interactions with the cell membranes and exchange play a role. Therefore, a differentiation between the various contributions to the average NMR signal in in vivo studies represents a difficult task. In this work, we have performed random-walk Monte Carlo simulations in model systems aiming at establishing the quantitative relations between the dynamics and microstructure. A detailed analysis of the average diffusion propagators and the corresponding signal attenuations is presented and the implications for experimental studies are discussed.
1574. Discovering White Matter Structure Beyond Fractional Anisotropy Maps
Jakub Piatkowski1, Amos J. Storkey2, Mark E. Bastin3
1Neuroinformatics Doctoral Training Centre, University of Edinburgh, Edinburgh, United Kingdom; 2Institute for Adaptive and Neural Computation, School of Informatics, University of Edinburgh, Edinburgh, United Kingdom; 3Medical Physics, University of Edinburgh, Edinburgh, Midlothian, United Kingdom
We use a fully physical two-compartment model, comprising isotropic and anisotropic terms, to describe diffusion MRI data. The posterior distributions over the parameters of this model are estimated using sampling techniques. This yields maps of white matter (WM) volume, which reveal a level of structure missing in FA maps. Additionally, we get tensor parameters for the anisotropic compartment (i.e. WM), which provide a measure of fibre-specific anisotropy that doesn't suffer from partial volume effects.
1575. The Effects of Intracellular Organelles on the ADC of Water Molecules in Cells
Daniel C. Colvin1, Jerome Jourquin2, Junzhong Xu1, Mark D. Does1, Lourdes Estrada2, John C. Gore1
1Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; 2Cancer Biology, Vanderbilt University, Nashville, TN, United States
Diffusion-weighted MRI methods are commonly used to characterize changes in tissue structure that accompany such pathologies as stroke and cancer. However, the underlying biophysical mechanisms influencing the apparent diffusion coefficient (ADC) remain poorly understood. Temporal diffusion spectroscopy techniques, which probe diffusion times two orders of magnitude shorter than conventional pulsed gradient methods, were implemented in a study of packed human embryonic kidney cells treated with drugs that alter actin polymerization, microtubule formation, and Golgi structure. Results reveal that these techniques may provide a more sensitive probe of changes in intracellular structure compared to conventional methods.
1576. The Influence of Holmium-166 Loaded Microspheres on ADC Measurements Using DWI
Gerrit Hendrik van de Maat1, Peter R. Seevinck1, Chris J.G Bakker2
1Image Sciences Institute, Utrecht, Netherlands; 2Department of Radiology, University Medical Center, Utrecht, Netherlands
It was shown that the presence of HoMS attenuates the signal of diffusion weighted images leading to a ADC reduction of 0.1mm2/ms per mg/ml HoMS. The reduction of the ADC is caused by the additional gradients induced by the microspheres resulting in a additional weighting factor for calculation of the ADC which is not taken into account. The dependency of the ADC on concentration HoMS is an effect that should be considered when using DWI for evaluating tumor viability after radioembolization. Since the local concentration can range up to 15mg/ml, a potential underestimation of the ADC of 1.5mm2/ms can occur which may lead to wrong diagnostic conclusions.
1577. Influence of Brain Ischemia on Biexponential Water Diffusion MRI Signal Decay
Renaud Nicolas1, Xavier Franceries1, Jeremie Pariente1, Nicolas Chauveau1, François Chollet1, Pierre Celsis1
1UMR 825, INSERM; Imagerie cérébrale et handicaps neurologiques, F-31059 Toulouse, France, Metropolitan
Biexponential analysis of DWI isotropic contrast in a case of acute stroke is here presented. Main finding were an F(slow) rise that has the same anatomic localization that has DWI positive signal but physiologic T.
1578. Three-Dimensional Models of Tissue Microstructure for Simulating High-Precision Diffusion MRI Data
Eleftheria Panagiotaki1, Matt G. Hall1, Bernard Siow1,2, Mark F. Lythgoe2, Daniel C. Alexander1
1Centre for Medical Image Computing, Dept. of Computer Science, University College London, London, United Kingdom; 2Centre for Advanced Biomedical Imaging, University College London, London, United Kingdom
This work outlines a method to construct detailed three-dimensional geometric models of tissue microstructure using confocal laser scanning microscopy (CLSM) images. We use these models to simulate the diffusion MRI signal from the tissue by running random-walk simulations within the resulting mesh. The precise simulated data from our method provide a mechanism for evaluating the quality of simple parametric models and the parameter estimates they provide.
1579. Effect of Gradient Pulse Duration on Diffusion-Weighted Imaging Estimation of the Diffusional Kurtosis for the Kärger Model
Jens H. Jensen1, Joseph A. Helpern1
1Radiology, New York University School of Medicine, New York, NY, United States
The apparent diffusional kurtosis for the Kärger model is calculated as a function of the gradient pulse duration. It is found that the error relative to the true value is at most a few percent for the parameter range of interest for brain. This result helps to justify the use of larger gradient pulse durations for diffusion-weighted imaging estimation of the diffusional kurtosis.
1580. Measuring Microstructural Features Related to Neuronal Activation Using Diffusion MRI and Three-Compartment Diffusion Models: A Feasibility Study
Irina Kezele1, Daniel C. Alexander2, Philip Batchelor3, Jean-François Mangin1, Denis Le Bihan1, Cyril Poupon1
1NeuroSpin, CEA, Gif-sur-Yvette, France; 2University College , London, United Kingdom; 3King's College , London, United Kingdom
We propose an analytic three-compartment diffusion model to explain the diffusion signal coming from tissues that are assumed to comprehend the intracellular and extracellular “free” water pools and a “membrane-bound” water pool, as hypothesized in a recent paper by Le Bihan (Phys. Med. Biol. 2007). Using this model we deliver an optimized imaging protocol to measure the relevant model parameters. Simulation experiments demonstrate the accuracy of estimating all the model parameters. In particular, the accurate estimation of membrane-water compartment size promotes the potential to detect the changes of this size that has been suggested to be related to neuronal activation.
1581. On the Influence of the Temporal Gradient Profile on the Apparent Diffusion Coefficient in the Motional Narrowing Regime in Closed Geometries
Frederik Bernd Laun1, Bram Stieltjes
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Baden-Württemberg, Germany
In DWI, the apparent diffusion coefficient is determined by both, the diffusion process and the temporal profile of the diffusion gradients. In this work a technique to determine the influence of the temporal gradient profile on the measured ADC is developed for the motional narrowing regime in closed geometries. It yields a direct series expansion in powers on inverse time. It is shown that the discontinuities and integrals over the derivatives of the gradient profile determine the constants of this series expansion.
Dmitry S. Novikov1, Valerij G. Kiselev2
1Radiology, NYU School of Medicine, New York, NY, United States; 2Medical Physics, Diagnostic Radiology, Uniklinikum Freiburg, Freiburg, Germany
MR signal is massively volume-averaged. Which parameters of tissue microstructure can survive this averaging, and be quantified by MRI? An answer is given by the effective medium description of tissues yielding the voxel-averaged equation for the magnetization. Heterogeneous diffusivity, relaxation rate and Larmor frequency offset give rise to corrections to the magnetization dynamics. The quantifiable tissue parameters are the distinct length scales on which the local diffusivity, relaxation rate and Larmor frequency vary. The effective medium approach unifies diffusion and relaxation, focussing on the single quantity whose frequency and wavevector dependence contains all measurable information about tissue heterogeneity.
Matthew R. Orton1, David J. Collins1, Dow-Mu Koh2, Michael Germuska1, Martin O. Leach1
1CR-UK and EPSRC Cancer Imaging Centre, Institute of Cancer Research, Sutton, Surrey, United Kingdom; 2Department of Radiology, Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom
Many models have been proposed for describing diffusion-weighted data, but as the environment of the diffusion process is known to be very complex in biological systems, choosing an appropriate model is difficult. We present a Bayesian methodology for estimating the posterior probability (uncertainty) of a given selection of diffusion models, applied to clinical DWI data. This is of interest to indicate statistical model uncertainty, and therefore uncertainty in the interpretation of the data. By penalising over complicated models, this methodology provides diffusion metrics that are more stable, and therefore more sensitive to a wider range of treatment effects.
Dmitry S. Novikov1, Valerij G. Kiselev2
1Radiology, NYU School of Medicine, New York, NY, United States; 2Medical Physics, Diagnostic Radiology, Uniklinikum Freiburg, Freiburg, Germany
We consider the DWI signal from any medium (tissue) in which the diffusion coefficient varies in space. Using recently developed effective-medium approach, we relate the signal to the diffusivity correlation function. Explicit formulas for time-dependent diffusion coefficient and diffusional kurtosis are provided in the case when the local diffusivity varies on a well-defined length scale. Our results are numerically confirmed by the Monte-Carlo simulation of diffusion in a two-dimensional model tissue. While the DWI signal has an approximately biexponential form, it is shown to be qualitatively different from that of the two-compartment exchange (Kärger) model.
1585. From Single- To Double-PFG: Gleaning New Microstructural Information in Complex Specimens
Noam Shemesh1, Evren Özarslan2, Peter J. Basser2, Yoram Cohen1
1School of Chemistry, Tel Aviv University, Tel Aviv, Israel; 2Section on Tissue Biophysics and Biomimetics, NICHD, National Institutes of Health, Bethesda, MD, United States
Although single-pulsed-field-gradient (s-PFG) methodologies such as DTI and the q-space approach are widely used to probe tissue microstructures, they suffer from inherent limitations, especially when specimens are characterized by randomly oriented compartments or size distributions. The double-PFG (d-PFG) is emerging as a new probe for novel microstructural information that cannot be achieved by other means. Here we demonstrate that d-PFG can be used to extract accurate compartment dimensions at low q-values both in phantoms and in biological cells which are randomly oriented, and in optic and sciatic nerves. The d-PFG may become an important MRI method in the CNS.
1586. New Quantitative Indices for DWI of the Brain Tissue at High B-Values
Farida Grinberg1, Ezequiel A. Farrher1, Joachim Kaffanke1, Ana-Maria Oros-Peusquens1, N. Jon Jon Shah1,2
1Medical Imaging Physics, Institute of Neuroscience and Medicine 4, Forschungszentrum Juelich GmbH, Juelich, Germany; 2Department of Neurology, Faculty of Medicine, RWTH Aachen University, Aachen, Germany
Diffusion MRI permits non-invasive probing of tissue microstructure and function and provides invaluable information in brain diagnostics. Conventional methods, however, are designed to retrieve only the average diffusion characteristics and tend to ignore deviations from simple Gaussian behaviour. Recently, increasing efforts have been dedicated to the development of the advanced approaches capable of capturing more detailed information on the propagation mechanisms. In this work, we report an in vivo diffusion study of the brain based on a detailed analysis of the attenuation patterns. New quantitative indices are suggested as map parameters and their potential use with respect to studies of the brain is discussed.
1587. Challenges in Reconstructing the Propagator Via a Cumulant Expansion of the One-Dimensional Q-Space MR Signal
Aurobrata Ghosh1, Evren Özarslan2, Rachid Deriche3
1Project Team Odyssée, INRIA Sophia Antipolis - Méditerannée, Sophia Antipolis , Alpes Maritimes, France; 2Section on Tissue Biophysics and Biomimetics, NICHD, National Institutes of Health, Bethesda, MD, United States; 3INRIA Sophia Antipolis - Méditerannée, email@example.com, Sophia Antipolis, Alpes Maritimes, France
We validate the GDTI with Gram-Charlier series approximation of the propagator approach in 1D, by comparing the Gram-Charlier and the Edgeworth series on closed form diffusion propagators with known cumulants. We also compare against estimated cumulants. We conclude that the Edgeworth series outperforms the Gram-Charlier series when the cumulants are known, but estimating the cumulants from the signal is numerically an important and sensitive problem.
1588. Detecting Restriction Using Non-Parametric Modelling of Diffusion MR Data
Saad Jbabdi1, Karla Laureen Miller1, Adrian R. Groves
1FMRIB Centre, University of Oxford, Oxford, United Kingdom
There is a growing interest in biophysical mechanisms for the diffusion contrast, with the exciting perspective of quantifying brain tissue microstructure (e.g. axon size and density). In particular, modelling restriction effects in the signal allows us to estimate the size of restricting structures. It is not clear, however, to what extent the signal acquired in vivo is sensitive to restriction. We suggest a non-parametric approach (no biophysical model assumed) to quantify restriction effects in the diffusion data. This method can be used either as a diagnostic tool or for experimental design.
1589. Implementation of the Equilateral Triangle in the Multiple Correlation Function Approach as Model Geometry for Restricted Diffusion.
Frederik Bernd Laun1, Bram Stieltjes
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Baden-Württemberg, Germany
The multiple correlation function approach uses the eigensystem of the Laplace operator to compute the effect of diffusion weighting gradients much more efficiently than Monte-Carlo simulations. However the applicability is limited since the governing matrices could only be computed for few model systems. Here we present the solutions for a further model system, the equilateral triangle. One interesting finding is that the apparent diffusion coefficient for this confining geometry is not dependent on the gradient orientation for moderate b-values, while a clear orientation dependency is observed for high b-values.
1590. The Effect of Metric Selection on Averaging Diffusion Tensors – When and Why Do Tensors Swell?
Ofer Pasternak1, Nir Sochen2, Peter J. Basser3
1Brigham and Women's Hosptial, Harvard Medical School, Boston, MA, United States; 2Tel Aviv University, Israel; 3Section on Tissue Biophysics & Biomimetics (STBB), National Institutes of Health (NIH), Bethesda, MD, United States
Metric selection is an essential step in performing diffusion tensor analysis, and here we investigate the selection effect on the estimation of FA, ADC and volume of mean tensors. We use Monte-Carlo simulations to generate noisy replicates, and compare estimations using a Euclidean and a Log-Euclidean metrics. The Log-Euclidean metric decreases tensor swelling, however, it is found to introduce other types of estimation biases. We find that for the case of thermal MR noise (rician), the swelling effect reduces estimation bias, and conclude that the Euclidean metric is an appropriate selection.
1591. An Improved Method for Diffusional Kurtosis Estimation
Babak A. Ardekani1,2, Ali Tabesh, 1,3, Jens H. Jensen3, Joseph A. Helpern, 1,3, Alvin Bachman1, Howard Kushner4
1Center for Advanced Brain Imaging, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, United States; 2Department of Psychiatry, New York University School of Medicine, New York, United States; 3Department of Radiology, New York University School of Medicine, New York, NY, United States; 4Statistical Sciences and Research Division, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, United States
In diffusional kurtosis imaging (DKI), the non-Gaussian nature of water diffusion in biological tissue is characterized by a kurtosis parameter, estimated in every voxel from a set of diffusion-weighted image acquisitions. This paper presents an improved method for estimating the kurtosis parameter in DKI. The specific contributions of this paper are twofold. (1) We propose a new method for imposing a positive-definiteness constraint on the fourth order tensor estimates and show its particular importance in DKI. (2) We propose using Mardia’s multivariate definition of kurtosis to characterize non-Gaussian diffusion, as opposed to mean univariate kurtosis used in previous publications.
1592. Supertoroid-Based Fusion of Cardiac Dt-Mri with Molecular and Physiological Information
Choukri Mekkaoui1,2, Marcel Jackowski3, Roberto Martuzzi1, Albert Sinusas1
1Yale University School of Medicine, New Haven, CT, United States; 2Harvard Medical School, Boston, MA, United States; 3University of São Paulo
The supertoroid-based representation enhances the three-dimensional perception of biological tissue structure and organization using DT-MRI. The presence of two additional free parameters in the supertoroidal function allows the tuning of the glyph surface in order to highlight different structural properties. Alternatively, these parameters can be used to fuse the visualization of structure with complimentary information provided by other modalities. In this work, we combined DT-MRI, MMP-targeted 99mTc-labeled radiotracer (RP805) uptake, and 201Tl perfusion on a porcine heart at 2-weeks post-MI, showing that the supertoroidal model can fuse information arising from different modalities into a unique and comprehensive visualization scheme.
1593. Maximum Likelihood Analysis Provides Accurate ADC Estimates from Diffusion-Weighted Prostate Images Acquired with Multichannel Coils
Louisa Bokacheva1, Yousef Mazaheri1,2, Hedvig Hricak2, Jason Koutcher1
1Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, United States; 2Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, United States
Diffusion-weighted (DW) MR images are contaminated with Rician noise, which leads to bias in ADC estimates. We explore accuracy and precision of calculating ADC from DW images acquired with multiple receiver channels using noise-corrected maximum likelihood estimation and uncorrected nonlinear least-squares fitting and log-linear fitting. Using Monte Carlo simulations, phantom and in vivo imaging of human prostate we demonstrate that accounting for Rician noise is important for images with variable SNR, for data acquired with phased arrays, and for achieving the maximum contrast between tissues with low and high ADC, which is often required for discriminating cancer and benign tissues on ADC maps.
Sarah Charlotte Mang1,2, Ania Busza, 2,3, Susanne Reiterer2, Wolfgang Grodd2, Uwe Klose2
1SIDT, German Cancer Research Center, Heidelberg, Germany; 2Section Experimental MR, Dept. of Neuroradiology, University Hospital Tuebingen, Tuebingen, Germany; 3MD/PhD Program, University of Massachusetts Medical School, Worcester, MA, United States
Fast and accurate segmentation of thalamic nuclei is important for clinical applications. We validated a segmentation method that is based on the classification of the local diffusion direction. We could show the correspondence between our segmentation results and anatomy known from a stereotactic atlas by Morel et al. in a group study of 63 healthy subjects. To show the similarity of individual subject results we compared the center-of-mass coordinates of the individual clusters and could show that they correspond well to each other.
Luca Nocetti1, Matteo Orlandi2, Davide Duzzi2, Patrizia Baraldi2, Carlo Adolfo Porro2
1Servizio Fisica Sanitaria, Az Osp.Univ. "Policlinico", Modena, Italy; 2Dipartimento di Scienze Biomediche, Università di Modena e Reggio Emilia
The human premotor cortex is likely to include a mosaic of anatomically and functionally distinct areas, as in non-human primates, but its functional networks are only beginning to be understood. In this work we use the DTI technique to investigate the anatomical connectivity between the premotor cortex and the other part of the brain. Data were processed using probabilistic tractography (FDT tool included in FSL package) Single subject analysis was performed in different ways in order to check for repeatability. In particular we tested the eddy current correction step (ECC) as implemented in FSL package and different paths of coregistration. Multi-subjects analysis was performed in a fashion based on the results of the single-subject analysis. Through single-subject analysis an optimized processing procedure was defined. The multi-subject analysis revealed 4 main regions with different anatomical connectivity
1596. Segmentation of Ischemic Lesion from Diffusion Weighted MRI and MR Apparent Diffusion Coefficient Maps
yohan attal1, Charlotte Rosso2, Yves Samson2, Sylvain Baillet3
1CRICM - CNRS UMR7225, Paris, France, Metropolitan; 2AP-HP-Urgences Cérébro-Vasculaires, Paris, France, Metropolitan; 3MEG Program, Department of Neurology, Medical College of Wisconsin-Froedtert Hospital, Milwaukee, US
We developed a fast and robust method to automatically segment ischemic lesions from a combination of acute diffusion-weighted MRI and apparent diffusion coefficient image volumes. This new segmentation technique extracts the ischemic areas from standard, clinical DWI image volumes of patient (N=40) with acute middle cerebral artery (MCA) stroke symptoms from the La Salpêtrière stroke center (Paris, France) database.
1597. TORTOISE: An Integrated Software Package for Processing of Diffusion MRI Data
Carlo Pierpaoli1, Lindsay Walker1, Mustafa Okan Irfanoglu1, Alan Barnett1, Peter Basser1, Lin-Ching Chang1, Cheng Guan Koay1, Sinisia Pajevic1, Gustavo Rohde1, Joelle Sarlls1, Minjie Wu1
1NIH, Bethesda, MD, United States
TORTOISE is an integrated and flexible software package for processing of DTI data, and in general for the correction of diffusion weighted images to be used for DTI and potentially for high angular resolution diffusion imaging (HARDI) analysis. It is non-commercial, and is freely available for download at www.tortoisedti.org.
1598. Novel Whole Brain DTI Segmentation and Diffusion Colour Mapping Technique for Tumour Diagnosis and Boundary Delineation
Timothy Lloyd Jones1, Ai Wern Chung2, B Anthony Bell1, Thomas Richard Barrick2
1Academic Neurosurgery Unit, St George's University of London, London, United Kingdom; 2Centre for Clinical Neurosciences, St George's University of London, London, United Kingdom
Accurate delineation of brain tumour boundaries is crucial for diagnosis, surveillance and treatment planning (e.g. image guided cyto-reductive surgery or radiotherapy). We propose a novel whole brain k-medians diffusion tensor imaging (DTI) algorithm generating Diffusion Colour Maps (DCMs) incorporating T2 relaxation, isotropic (p) and anisotropic (q) characteristics. In this study, we have applied our technique to a variety of intracranial pathology revealing characteristic colour patterns for each lesion type and clearly delineated tumour boundaries, suggesting a potential role in diagnosis and treatment planning.
1599. Featured Based Deformable Registration of Diffusion MRI Using the Fiber Orientation Distribution
Luke Bloy1, Ragini Verma2
1Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, United States; 2Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
Diffusion tensor imaging (DTI) has developed into an important tool for the study of WM diseases such as multiple sclerosis, as well as neurodevelopmental disorders, such as schizophrenia, epilepsy and autism. DTI is however limited in its ability to model complex white matter, which has prompted the development of higher order models(HOMs). Before HOMs can be used for group based statistical studies, algorithms for spatial normalization must be developed. We present a registration framework for images of fiber orientation distributions, a common HOM, which uses rotationally-invariant features of the FOD to drive a multi-channel diffeomorphic demons algorithm.
Paulo Rodrigues1, Andrei Jalba2, Pierre Fillard3, Anna Vilanova1, Bart M. ter Haar Romeny1
1Biomedical Image Analysis, Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands; 2Department of Computer Science, Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands; 3CEA, Paris, France
The investigation of Diffusion Tensor Imaging (DTI) data is of complex and exploratory nature: tensors, fiber tracts, bundles. This quickly leads to clutter problems in visualization as well as in analysis. We propose a new framework for the multi-resolution analysis of DTI. Based on fast and greedy watersheds operating on a multi-scale representation of a DTI image, a hierarchical depiction of such image is determined conveying a global-to-local view of the fibrous structure of the analysed tissue. We present a simple and interactive segmentation tool, where different bundles can be segmented at different resolutions.
1601. Optimization of Body-Centered-Cubic Encoding Scheme for Diffusion Spectrum Imaging
Li-Wei Kuo1, Wen-Yang Chiang2, Fang-Cheng Yeh, 1,3, Van Jay Wedeen4, Wen-Yih Isaac Tseng1,5
1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2Center for Bioengineering and Bioinformatics, The Methodist Hospital Research Institute and Department of Radiology, The Methodist Hospital, Houston, TX, United States; 3Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States; 4MGH Martinos Center for Biomedical Imaging, Harvard Medical School, Charlestown, MA, United States; 5Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan
The present study investigated the optimum parameters for body-centered-cubic sampling scheme as well as its accuracy of mapping complex fiber orientations compared with grid sampling scheme of diffusion spectrum imaging. A systematic angular analysis was performed on in-vivo data simulation and verification studies. Ours results showed that body-centered-cubic sampling scheme provided an incremental advantage in angular precision over the grid sampling scheme. Further, the capacity of half-sampling schemes based on the concept of q-space symmetry was also demonstrated. By considering the efficiency, this study showed that body-centered-cubic and half-sampling schemes may be potentially helpful for future clinical applications.
1602. Systematic Comparison of DTI at 7T and 3T: Assessment of FA for Different Acquisition Protocols and SNR in Healthy Subjects
Seongjin Choi1, Dustin Cunningham1, Francisco Aguila1, John Corrigan2, Jennifer Bogner2, Walter Mysiw2, Donald Chakeres1, Michael V. Knopp1, Petra Schmalbrock1
1Radiology, The Ohio State University, Columbus, OH, United States; 2Physical Therapy & Rehab, The Ohio State University
As a part of optimization of diffusion tensor imaging (DTI) at 7T, we explored how voxel shape, voxel volume, and directional resolution affected FA measurement in normal aging brains at 7T and 3T. We observed statistically identical slopes while significantly different offset between the regression lines for FA along with age. In the study of SNR and FA over a range of reduction factors, we found that reduction factor affected standard deviation of measured FA values instead of FA itself.
1603. Optimal HARDI Acquisition Schemes for Multi-Tensor Models
Benoit Scherrer1, Simon K. Warfield2
1Department of Radiology, Computational Radiology Laboratory , Boston, MA, United States; 2Department of Radiology, Computational Radiology Laboratory, Boston, MA, United States
We show that multi-tensor models cannot be properly estimated with a single-shell HARDI acquisition because the fitting procedure admits a infinite number of solutions, melding the estimated tensors eigenvalues and the partial volume fractions. As a result, a uniform fiber bundle across its entire length may appear to grow and shrink as it passes through voxels and experiences different partial volume effects. Only the use of multiple-shell HARDI acquisitions allows the system of equations to be better determined. We provide numerical experiments to explore the optimal acquisition scheme for multi-tensor imaging.
1604. Effects of Turboprop Diffusion Tensor Imaging Acquisition Parameters on the Noise of Fractional Anisotropy
Ashish A. Tamhane1, Konstantinos Arfanakis1
1Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, United States
The goal of this study was to investigate the effect of the number of blades, echo-train length (ETL), turbo-factor, and number of diffusion directions on the noise of fractional anisotropy (FA) in Turboprop diffusion tensor imaging (DTI). It was shown that the range of FA standard deviation (stdFA) values for different tensor orientations was lower when more diffusion directions were used. Additionally, stdFA decreased for an increasing number of blades, lower ETL, and lower turbo-factor. Hence, in Turboprop-DTI, optimal FA noise characteristics can be achieved by increasing the number of diffusion directions and blades, and decreasing the ETL and turbo-factor.
1605. The Influence of Trapezoidal Gradient Shape on the B-Factor of Hyperecho Diffusion Weighted Sequences
Stefanie Schwenk1, Matthias Weigel1, Valerij G. Kiselev1, Juergen Hennig1
1Department of Diagnostic Radiology, University Hospital Freiburg, Medical Physics, Freiburg, Germany
Diffusion weighted Hyperecho Imaging has maintained some interest during the last years since it has the potential to offer a probe for tissue microstructure. The present work studies the influence of idealized rectangular gradient shapes on the quantitation of effective b-factors in diffusion weighted Hyperecho preparation schemes for a variety of MR parameters.
1606. Improving High-Resolution Q-Ball Imaging with a Head Insert Gradient: Bootstrap and SNR Analysis
Julien Cohen-Adad1,2, Jennifer A. McNab1,2, Thomas Benner1,2, Maxime Descoteaux3, Azma Mareyam1, Van J. Wedeen1,2, Lawrence L. Wald1,2
1A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology, MGH, Charlestown, MA, United States; 2Harvard Medical School, Boston, MA, United States; 3MOIVRE Centre, Department of Computer Science, Université de Sherbrooke, Sherbrooke, QC, Canada
Head-insert gradients are particularly suitable for diffusion-weighted (DW) imaging due to a higher maximum strength, higher switching rate and higher duty cycle. In this paper we evaluate the performance of a head-insert combined with 32ch coil at 3T compared to conventional body gradients, for high spatial and angular resolution diffusion-weighted imaging. Bootstrap-based metrics demonstrate higher reproducibility of the Q-Ball estimate and lower uncertainty on the extracted maxima of the diffusion orientation distribution function.
1607. A Connectome-Based Comparison of Diffusion MR Acquisition Schemes
Xavier Gigandet1, Tobias Kober2,3, Patric Hagmann1,4, Leila Cammoun1, Reto Meuli4, Jean-Philippe Thiran1, Gunnar Krueger2
1Signal Processing Laboratory (LTS5), Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 2Advanced Clinical Imaging Technology, Siemens Schweiz AG-CIBM, Lausanne, Switzerland; 3Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 4Department of Radiology, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland
Diffusion MRI has evolved towards an important clinical and research tool. Though clinical routine is mainly using diffusion tensor imaging (DTI) approaches, q-ball imaging (QBI) and diffusion spectrum imaging (DSI) have become often used techniques in research oriented investigations. In this work, we aim at assessing the performance of various diffusion acquisition schemes by comparing the respective whole brain connection matrices. The results from the analysis indicate that (a) all diffusion scans produce a biologically meaningful mapping of the human connectome, and (b) more non-dominant fiber populations, e.g. neighboring association fibers in the 60-90 mm range, are better revealed with more complex diffusion schemes.
1608. Effects of Diffusion Time on Diffusion Tensor Derived Parameters Measured on the Rat Brain at Ultrahigh Magnetic Field
Yohan van de Looij1,2, Nicolas Kunz1,2, Petra S. Hüppi1, Rolf Gruetter2,3, Stéphane V. Sizonenko1
1Division of Child Growth & Development, Department of Pediatrics, University of Geneva, Geneva, Switzerland; 2Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 3Department of Radiology, University of Geneva and Lausanne, Geneva and Lausanne, Switzerland
A large number of small bore systems propose implemented sequences making easy the use of DTI but the choice of sequence parameters can have a huge impact on the derived tensor quantifications. The aim of this work was to study the influence of diffusion time (td) and brain microstructures on diffusion derived parameters in the rat brain at 9.4T. 3 repeated DTEPI images (4 shots) were performed with td = 10, 25 and 39 ms respectively. This study shows in white and gray matter a dependence of diffusion derived parameters on td from 10 ms to 25 ms.
1609. Using Statistical Resampling and Geometric Least Squares to Improve DTI Measures Efficiently
Paul Andrew Taylor1, Bharat B. Biswal1
1Radiology, UMDNJ, Newark, NJ, United States
An efficient method for improving DTI analysis is presented; geometric fitting and statistical resampling are used to calculate diffusion ellipsoids and associated quantities of interest with confidence intervals, and to greatly reduce the necessary number of gradient measures and therefore the scan time.
1610. Isotropic High Resolution Diffusion-Tensor Imaging in Humans at 7T
Robin Martin Heidemann1, Alfred Anwander1, Thomas Knoesche1, Thorsten Feiweier2, Fabrizio Fasano3, Josef Pfeuffer2, Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; 2Siemens Healthcare Sector, Erlangen, Germany; 3Fondazione Santa Lucia, Rome, Italy
For isotropic high resolution DTI at ultra-high field strength, susceptibility effects and T2* decay must be properly addressed. A combination of reduced FOV imaging (zoomed imaging) and parallel imaging is optimized here, achieving high acceleration factors. This approach enables DWI acquisitions with 1 mm isotropic resolution at 7T. The high quality of the DTI data provides a high level of anatomical details.
1611. Reduced-FOV Diffusion Imaging with ZOnal Oblique Multislice (ZOOM) Combined with Readout-Segmented (RS)-EPI
Samantha J. Holdsworth1, Stefan Skare1, Rafael Luis O'Hallaran1, Roland Bammer1
1Radiology, Stanford University, Palo Alto, CA, United States
Diffusion-weighted imaging (DWI) using EPI has been limited by geometric distortion and blurring, particularly in regions with large off-resonance effects. Distortions can be reduced by reducing the phase-encode FOV, and by reducing the echo-spacing. For the former, we implement the ZOnal Oblique Multislice (ZOOM) technique, which uses a tilted refocusing pulse to spatially select a region of interest. To reduce echo-spacing further, we use the readout-segmented (RS)-EPI technique. We show that the combination of the ZOOM pulse and RS-EPI results in images of the spine and orbits with reduced geometric distortion.
1612. Robust Fat Suppression for High-Resolution Diffusion-Weighted Imaging
Joelle E. Sarlls1,2, Wen-Ming Luh3, Carlo Pierpaoli1
1NICHD, National Institutes of Health, Bethesda, MD, United States; 2Henry M. Jackson Foundation, Rockville, MD, United States; 3NIMH, National Institutes of Health, Bethesda, MD, United States
Although spectral-spatial excitation pulses provide single-shot EPI diffusion-weighted images without signal from fat, they are limited in the attainable minimum slice thickness. To achieve higher resolution, traditional fat supression methods must be used. In this work, an exhaustive investigation was performed to determine which, if any, implementation of the slice-selective gradient reversal method completely supressed the fat signal. The dual-spin-echo diffusion preparation implementation, with opposite polarity slice-select gradients for the two 180° refocusing pulses, combined with traditional fat supression was found to completely suppress fat in phantoms and in vivo.
1613. Improved Prospective Optical Motion Correction for DTI Using an Extended-Field-Of-View and Self-Encoded Marker
Murat Aksoy1, Christoph Forman1, Matus Straka1, Samantha Jane Holdsworth1, Stefan Tor Skare1, Juan Manuel Santos2, Joachim Hornegger3, Roland Bammer1
1Department of Radiology, Stanford University, Stanford, CA, United States; 2Electrical Engineering, Stanford University, Stanford, CA, United States; 3Computer Science, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
Due to the prolonged acquisition time, correction of rigid-head motion artifacts is essential for diagnostic image quality in diffusion tensor imaging (DTI). In this study, we performed prospective, real-time rigid head motion correction for DTI. This is achieved by using a single camera mounted on a head coil together with a 3D, self-encoded checkerboard marker that is attached to the patient's forehead. The results show that the proposed setup is very effective in removing rigid head motion artifacts even for very motion-sensitive scans, such as DTI.
1614. High Angular Resolution Diffusion Imaging (HARDI) with Highly Constrained Back Projection Reconstruction (HYPR)
Yu-Chien Wu1, Charles A. Mistretta2, Andrew L. Alexander3, Trevor Andrews4, Paul J. Whalen5, James V. Haxby5
1Dartmouth Brain Imaging Center, Dartmouth College, Hanover, NH, United States; 2Wisconsin Institutes for Medical Research, University of Wisconsin-Madison, Madison, WI, United States; 3Medical Physics, University of Wisconsin-Madison, Madison, WI, United States; 4College of Medicine, University of Vermont, Burlington, VT, United States; 5Psychological & Brain Sciences, Dartmouth College, Hanover, NH, United States
High angular resolution diffusion imaging (HARDI) has drawn considerable attention for its powerful directional measure on predicting fiber orientation at the level of subvoxel dimension. HARDI may improve the accuracy of WM tractography, which leads to an important application of brain structural connectivity. However, due to the higher diffusion weighting (DW) b-value and substantial number of DW directions, its long scan time is often the obstacle for extensive clinical application. In this study, we investigate the feasibility of the new reconstruction method, highly constrained back projection reconstruction, which may significantly reduce HARDI scan time.
1615. 3D PROPELLER-Based Diffusion Weighted Imaging with Improved Robustness to Motion
Eric Aboussouan1, Jim Pipe1
1Barrow Neurological Institute, Phoenix, AZ, United States
The previously described ROTOR (Radially Oriented Tri-Dimensionally Organized Readouts) pulse sequence allows 3D DWI with high SNR efficiency and lower SAR compared to DW FSE and reduced off-resonance artifacts and improved 3D phase correction compared to DW EPI. This work describes improvements in the pulse sequence and reconstruction scheme allowing greater robustness to motion. Blades are made wider by combining odd and even non-CPMG echoes and are gridded off-center to effectively reflect the linear component of the motion phase.
1616. Multi-Shot SENSE DWI at 7T
Ha-Kyu Jeong1,2, Adam W. Anderson1,2, John C. Gore1,2
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States; 2Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States
We developed a simple reconstruction method for multi-shot SENSE diffusion weighted data using an interleaved EPI sequence. The reconstruction was done independently for each column of the image by combining image unwrapping and phase corrections. To estimate shot-to-shot phase variations due to subject motion during diffusion encoding, a 2-D navigator-echo acquisition was used following the image-echo acquisition. Both of the echo acquisitions were SENSE accelerated reducing scan duration, susceptibility and T2* effects. Our reconstruction method and pulse sequence produced diffusion weighted images free of ghost artifacts at 7 Tesla.
1617. Whole-Blade PROPELLER DWI
Chu-Yu Lee1, Zhiqiang Li2, Eric Aboussouan1, Josef P. Debbins, 1,3, James G. Pipe3
1Electrical Engineering, Arizona State University, Tempe, AZ, United States; 2GE Healthcare, Waukesha, WI, United States; 3Keller Center for Imaging Innovation, Barrow Neurological Institute, Phoenix
PROPELLER  is a variant of multi-shot FSE technique, providing a high-resolution DWI with excellent immunity to off-resonance. Its self-navigated nature around the center of K-space also allows for motion correction. The odd/even echo phase inconsistencies in the non-CPMG echo train were addressed using the ¡§split-blade¡¨ method , where the blade width was reduced by a factor of two, making the motion-related phase more difficult to remove . Thus, this work applied the ¡§whole blade¡¨ method  to create wider blades for robustly removing the motion-induced phase. The proposed scheme added the reference blade (only for b=0) to effectively remove the coil phase of odd/even echoes. This reference blade can also be used for GRAPPA kernel training for parallel imaging to further widen the blade width and reduce the scan time.
1618. High Resolution 3D Multi-Slab Multi-Shot Spin Echo Diffusion-Weighted Imaging
Anh Tu Van1, Dimitrios C. Karampinos2, Bradley P. Sutton3,4
1Electrical and Computer Engineering, University of Illinois, Urbana, IL, United States; 2Radiology and Biomedical Imaging, University of California, San Francisco, CA, United States; 3Bioengineering, University of Illinois, Urbana, IL, United States; 4Beckman Institute, University of Illinois, Urbana, IL, United States
High isotropic resolution diffusion-weighted imaging is required in order to reduce partial volume effects in the estimation of diffusion metrics. In the present work, a novel high resolution 3D spin echo diffusion-weighted acquisition strategy is proposed. The acquisition is time efficient, fairly immune to gross motion and pulsation effects, and has a simple diffusion-weighted signal model. High quality, high resolution (1.88 x 1.88 x 1.88 mm3) diffusion-weighted images, FA maps, color-coded FA maps (13 directions) with whole brain coverage were achieved within a reasonable scan time.
1619. Isotropic Resolution in Diffusion Weighted Imaging Using 3D Multi-Slab, Multi-Echo Echo Planar Imaging
Mathias Engström1,2, Anders Nordell1,2, Magnus Mårtensson1,2, Bo Nordell1, Roland Bammer3, Stefan Skare, 2,3
1Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden; 2Karolinska MR Research Center, Karolinska Institute, Stockholm, Sweden; 3Radiology, Stanford University, Stanford, CA, United States
A new readout strategy for 3D-DWI is proposed using EPI and multi-slab encoding, with the purpose of achieve sharp and thin slice profiles.
Rita G. Nunes1, Joseph V. Hajnal1
1Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom
As Diffusion-Weighted images are inherently very sensitive to motion, full brain coverage is achieved by imaging multiple 2D single shot slices. However, as most fiber tracts in the brain have a 3-dimensional structure, ensuring that the anatomy is fully sampled along all three dimensions is likely to be important. Conventionally, the same slice prescription is used for all diffusion sensitization directions. We demonstrate that by using overlapping slices and/or combining slices acquired along orthogonal directions higher fidelity anisotropy maps can be reconstructed. Using this type of geometry should also increase data robustness in the presence of more severe subject motion.
1621. Diffusion Weighted Turbo-STEAM ZOOM Imaging of the Lumbar Spine
Patrick Hiepe1, Karl-Heinz Herrmann2, Christian Ros2, Jürgen R. Reichenbach2
1Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena University Hospital , Jena, Germany; 2Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena University Hospital, Jena, Germany
So far, most clinical DWI applications have relied on EPI although DWI EPI is limited by susceptibility artifacts. STEAM MRI with robust turbo-FLASH readout is a fast imaging technique with subsecond measurement times. This robustness is traded against SNR by using a less signal efficient acquisition technique. To achieve maximum efficiency of the turbo-STEAM sequences a reduced number of PE lines is necessary. An effective way is to utilize the ZOOM imaging technique, which limits the excited FOV in the PE direction to include only the ROI. This can be used to measure various regions of the body with a narrow FOV, e.g. lumbar spine, without the occurrence of foldover or aliasing artifacts. In comparison with EPI, DW ZOOM single-shot STEAM MRI of the lumbar spine exhibits a reduced SNR, but avoids regional signal losses and geometric distortions. Furthermore, no fat suppression is necessary. Our case report indicates that the DW ZOOM turbo-STEAM MRI technique appears to be a good alternative to the standard DW EPI.
1622. Parallel Line Scan Diffusion Tensor Imaging
Renxin Chu1, Bruno Madore1, Lawrence P. Panych1, Stephan E. Marier1
1Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States
Diffusion tensor imaging (DTI) has been widely used in the study of white matter-related diseases. Single-shot echo-planar imaging (EPI) is usually the preferred technique, but EPI images may exhibit severe geometric distortions, especially near the skull base. Line scan diffusion imaging (LSDI) is a one-dimensional Fourier encoding technique with considerable robustness against motion and geometric distortions. We present a parallel LSDI diffusion tensor imaging technique with acceleration along two dimensions, with 3D whole brain coverage and four-fold acceleration. The speed-up remarkably comes at no cost in SNR, and preserves the LSDI immunity to susceptibility-induced signal losses and geometric image distortions.
1623. SIR-EPI Diffusion Imaging for 3-Fold Faster Scan Time to Enable Trade-Offs in Slice Coverage and Gradient Duty Cycle Reduction.
Sudhir Ramanna1, Vibhas Deshpande2, David Feinberg1,3
1Advanced MRI Technologies, Sebastopol, CA, United States; 2Siemens, United States; 3University of California, Berkeley, San Francisco, CA, United States
The use of high b-values encoded with lengthy high amplitude gradient pulses place limitations on diffusion imaging with HARDI techniques. In this work, we develop and evaluate SIR with two and three echoes per read period (SIR-2, SIR-3) for HARDI imaging. Both SIR-2 and SIR-3 EPI sequences are shown to be useful for simply reducing scan time, for obtaining higher resolution or field of view on the slice axis with more slices per TR or instead controlling the heat limitations using high b-values by reducing the gradient duty cycle in HARDI acquisitions.
Rita G. Nunes1, Ivana Drobnjak2, Stuart Clare3, Peter Jezzard3, Mark Jenkinson3
1Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom; 2Centre for Medical Image Computing, University College London, London, United Kingdom; 3Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, United Kingdom
Echo-planar diffusion-weighted images can display significant geometric distortions due to eddy current fields. Several diffusion preparation schemes have been proposed, which can null eddy currents with a single time constant. We use an MRI simulator to compare the performance of three such sequences in the presence of multiple components, and investigate whether affine registration is capable of correcting for the resulting distortions. Our study confirms that, in general, doubly-refocused sequences perform better than single spin-echo approaches, and suggest that when the use of two refocusing pulses is not desirable, it may be preferable to use a modified single spin-echo sequence.
1625. Homodyne Reconstruction of Partial Fourier Readout-Segmented EPI for Diffusion Imaging
Robert Frost1, David Andrew Porter2, Thorsten Feiweier2, Peter Jezzard1
1FMRIB Centre, University of Oxford, Oxford, United Kingdom; 2Siemens Medical Solutions, MR Applications Development, Erlangen, Germany
This study demonstrates that homodyne partial Fourier reconstruction can be used to reduce acquisition time in readout-segmented EPI with GRAPPA parallel imaging without significantly compromising image quality. Diffusion images and signal-to-noise ratio comparisons of full k-space and partial Fourier images are presented. By acquiring 6/11 readout segments, a 40% reduction in scan time could be achieved which would allow high-resolution tractography in clinically realistic time frames.
1626. Distortion Correction Method for Single Echo DTI at 7T MRI Using Non-Distortion and Distortion Dimension Combined PSF Mapping Technique
Se-Hong Oh1, Jun-Young Chung1, Sung-Yeon Park1, Daeshik Kim2, Myung-Ho In3, Maxim Zaitsev4, Oliver Speck3, Young-Bo Kim1, Zang-Hee Cho1
1Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, Republic of; 2Department of Electrical Engineering, Korea Advance Institute of Science and Technology, Daejeon, Korea, Republic of; 3Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany; 4Department of Radiologic Research, Medical Physics, University Hospital of Freiburg, Freiburg, Germany
To acquire high resolution DTI images at 7T, we should solve two major problems (One thing is reduce TE, another thing is correct geometric distortion). To minimize TE and increase SNR, we modified EPI based double echo diffusion sequence to EPI based single echo diffusion sequence. Afterwards we could reduce 16ms. To correct geometric distortion use distortion and non-distortion dimensional combined PSF correction method. Then we can correct the geometric distortion both compressed and stretched area more accurately.
1627. A Novel Robust Algorithm to Correct for Eddy Current Distortions in High B-Value Diffusion MRI
Henrik Hansson1, Jimmy Lätt, 12, Freddy Ståhlberg1,3, Markus Nilsson1
1Department of Medical Radiation Physics, Lund University, Lund, Sweden; 2Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; 3Department of Diagnostic Radiology, Lund University, Lund, Sweden
Eddy currents distort diffusion-weighted images, which give rise to artefacts in the estimated apparent diffusion coefficient and the diffusion kurtosis. Current correction methods are not effective for b-values greater than 1000 s/mm2. We have developed a correction algorithm based on comparison of all images in an image set, instead of separate volumes. This allows model based distortion correction by maximizing the local correlation of the entire image set.
Adriaan L. Moerland1, Elizabeth A. Moore2
1Advanced Development, Philips Healthcare BV, Best, Netherlands; 2MR Clinical Science, Philips Healthcare BV, Best, Netherlands
Diffusion MRI is increasingly important in clinical radiology, however the technique is very sensitive to system defects in the gradient chain. A new method has been developed for easy QA in diffusion MRI. The acquisition is 3 fast DTI scans on a spherical aqueous phantom, taking less than 3 minutes. Analysis is fully automated and derives measures of deformation of the circular phantom image as well as apparent diffusion coefficient ADC and fractional anisotropy FA values. Two of the deformation measures were found to be highly sensitive to gradient defects such as eddy current (mis)calibration.
Patrick William Hales1, Rebecca Burton2, Christian Bollensdorff2, Jurgen E. Schneider1
1Cardiovascular Medicine, Oxford University, Oxford, Oxon, United Kingdom; 2Physiology, Anatomy & Genetics, Oxford University, Oxford, Oxon, United Kingdom
The influence of both SNR and diffusion gradient sampling scheme on the precision and accuracy of high resolution (203 μm) DTI data acquired in the ex vivo rat heart has been investigated. We demonstrate how the use of reduced encoding of diffusion weighted images using the approximate generalized series reconstruction technique can increase SNR without increasing scan time, and how this can be employed to reduce the overall error in the primary eigenvector orientation.
1630. About the Origins of Diffusion-Weighting Due to the Non-Linear Phase Dispersion Induced by Frequency-Swept Pulses
Julien Valette1,2, Denis Le Bihan2, Franck Lethimonnier2
1CEA-MIRCen, Fontenay-aux-Roses, France; 2CEA-NeuroSpin, Gif-sur-Yvette, France
It has been recognized in the past that the non-linear phase induced by frequency-swept pulses may cause diffusion-weighting. In the present work, the origins of the non-linear phase dispersion induced by frequency-swept pulses are revisited, in order to assess whether the phase variation of the B1 field during the sweep should be explicitly considered when calculating diffusion weighting. Following this analysis, an analytical expression is derived for diffusion-weighting induced by a pair of slice selective hyperbolic secant pulses, and confronted to numerical simulation of the Bloch equations including diffusion.
1631. On the Accuracy of Diffusion Models for Fast Low-Angle Short-TR SSFP-Echo (FLASH-DW SSFP)
Oliver Bieri1, Carl Ganter2, Klaus Scheffler1
1Radiological Physics, University of Basel Hospital, Basel, Switzerland; 2Department of Diagnostic Radiology, Technical University Munich, Munich, Germany
Several models have been developed for the description of diffusion in steady-state free precession (SSFP) sequences. For clinical practice, high SNR and short acquisition times are desirable with DW-SSFP. In this work, a new approach for quantitative diffusion imaging is proposed using a fast low-angle short-TR (FLASH) diffusion-weighted (DW) SSFP sequence. The accuracy of diffusion models is assed in-vitro and the feasibility of high resolution quantitative diffusion mapping is demonstrated in-vivo for human articular cartilage.
1632. Simultaneously Measuring Axonal Diameter Distribution and Direction of Rat Brain Using Q-Space Diffusion Tensor Magnetic Resonance Imaging
1Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan
Fundamental relationships between diffusion tensor imaging (DTI) and q-space imaging can be derived which establish conditions when these two complementary MR methods are equivalent. When the 3D displacement distribution is measured by q-space imaging with large displacement and small q vector, the result is similar to 3D Gaussian assumed in DTI. Combing displacement information from q-space imaging and fiber direction from DTI, distribution of axonal diameters and directions could be derived at the same time. The study proposed a novel technique, q-space diffusion tensor imaging (qDTI), combined with two image reconstruction methods based on the assumption to simultaneously map axonal diameter distribution and direction of rat brain. One was tensor-based method. The 3D Gaussian displacement distribution could be obtained directly by the displacement tensor. The other was displacement projection method. The effective axonal diameter was defined as the average of several displacements projected to the direction of the fiber section. They provided MR images in which physical parameters of water diffusion such as the mean displacement and maximum diffusivity of water molecules were used as image contrast. Our results demonstrated that two qDTI methods both produced reasonable distribution of effective axonal diameters and directions in rat brain.
Irvin Teh1,2, Xavier Golay1,3, David Larkman2
1Lab of Molecular Imaging, Singapore Bioimaging Consortium, Singapore, Singapore; 2Imaging Sciences Department, Imperial College London, London, United Kingdom; 3Institute of Neurology, University College London, London, United Kingdom
A diffusion-weighted fast spin echo periodically rotated overlapping parallel lines with enhanced reconstruction (DW-FSE-PROPELLER) sequence was combined with a multiple axis Stejskal-Tanner diffusion weighting scheme that rotated and alternated across blades. This reduced the number of DW acquisitions needed to acquire the mean apparent diffusion coefficient from three to one, halving the total acquisition time. This motion and distortion robust method was tested in the in-vivo mouse brain and compared to previously proposed rotating DW strategies.
1634. Novel Diffusion-Diffraction Patterns in Double-PFG NMR Afford Accurate Microstructural Information in Size Distribution Phantoms
Noam Shemesh1, Evren Özarslan2, Peter J. Basser2, Yoram Cohen1
1School of Chemistry, Tel Aviv University, Tel Aviv, Israel; 2Section on Tissue Biophysics and Biomimetics, NICHD, National Institutes of Health, Bethesda, MD, United States
Diffusion-diffraction minima, which convey important microstructural information, vanish from the signal decay in single-pulsed-field-gradient (s-PFG) experiments conducted on specimens characterized by size distributions. The double-PFG (d-PFG) methodology, an extension of s-PFG, was recently predicted to exhibit zero-crossings (analogous to s-PFG diffusion-diffraction minima) that would persist even when the specimen is characterized by a broad size-distribution. We therefore studied the signal decay in both s- and d-PFG in size-distribution phantoms consisting of water-filled microcapillaries of various sizes. We find that the diffusion-diffraction minima in s-PFG indeed vanish, while the zero-crossings in d-PFG indeed persist, allowing to extract important microstructural information.
1635. Metrics for Distinguishing Axon Disorder from Demyelination in Regions of Decreased Fractional Anisotropy
Christine Marie Zwart1, David H. Frakes1,2, Josef P. Debbins3
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, United States; 2School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, AZ, United States; 3Keller Center for Imaging Innovation, St. Joseph's Hospital and Medical Center, Phoenix, AZ, United States
Many diseases of the white matter are accompanied by an observable decrease in fractional anisotropy as measured with Diffusion Tensor Imaging. This decrease can be attributable to a general increase in extracellular space or an absence of collinearity with respect to axon orientations. For studying the progression of diseases such as multiple sclerosis (demyelination) and epilepsy (disorder) we have developed a correlation based metric that distinguishes between these processes.
1636. Enhanced ICBM Diffusion Tensor Template of the Human Brain
Shengwei Zhang1, Huiling Peng1, Robert Dawe1, Konstantinos Arfanakis1
1Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, United States
The purpose of this study was to develop a diffusion tensor (DT) template that is more representative of the microstructure of the human brain, and more accurately matches ICBM space than existing templates. This was achieved by normalizing 67 DT datasets with minimal artifacts using high-dimensional non-linear registration. The normalization accuracy achieved for the 67 datasets was evaluated. The properties of the resulting template were compared to those of the current state of the art. The new template was shown to be more representative of single-subject human brain diffusion characteristics, and more accurately matches ICBM space than previously published templates.
1637. Variability of Diffusion Tensor Characteristics in Human Brain Templates: Effect of the Number of Subjects Used for the Development of the Templates
Shengwei Zhang1, John D. Carew2, Konstantinos Arfanakis1
1Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, United States; 2Dickson Institute for Health Studies, Carolinas Healthcare System, Charlotte, NC, United States
Development of a diffusion tensor (DT) brain template that is not biased by the properties of a single subject requires averaging of the DT information from multiple subjects. The purpose of this study was to investigate the variability of DT characteristics in templates developed using different numbers of subjects. The variability of template DT properties decreased as the number of subjects increased. Furthermore, DT templates constructed from 30 subjects demonstrated high stability in tensor properties of voxels with FA=(0.6,1]. When considering voxels with FA=(0.2-1], more than 60 subjects were necessary in order to achieve sufficiently high stability in tensor properties.
1638. Assessing the Accuracy of Spatial Normalization of Diffusion Tensor Imaging Data in the Presence of Image Artifacts
Anton Orlichenko1, Robert J. Dawe2, Huiling Peng2, Konstantinos Arfanakis2
1Electrical and Computer Engineering, Illinois Institute of Technology, Chicago, IL, United States; 2Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, United States
Use of diffusion tensor imaging (DTI) data with minimal image artifacts may enhance the accuracy of inter-subject spatial normalization. This effect was investigated by comparing the coherence of primary eigenvectors after normalizing separately a) data with minimal artifacts, and b) data with typical field inhomogeneity-related artifacts, acquired on the same subjects. Tensors derived from data with minimal artifacts were found to have higher primary eigenvector coherence in white matter, compared to tensors derived from data contaminated with image artifacts. These results demonstrate that achieving the most accurate spatial normalization of DTI data requires minimization of image artifacts.
1639. The Effect of Template Selection on Diffusion Tensor Imaging Voxel Based Analysis Results
Wim Van Hecke1,2, Caroline Sage2, Jan Sijbers3, Stefan Sunaert2, Paul M. Parizel1
1Department of Radiology, Antwerp University Hospital, Antwerp, Belgium; 2Department of Radiology, Leuven University Hospital, Leuven, Belgium; 3VisionLab, University of Antwerp, Antwerp, Belgium
In this work, we examined the effect of the template or atlas selection on the voxel based analysis results of diffusion tensor images. To this end, simulated data sets were used.
1640. Artificial Phantoms for Studies of Anisotropic Diffusion in the Brain
Ezequiel Alejandro Farrher1, Erasmo Batta1, Yuliya Kupriyanova1, Oleg Posnansky1, Farida Grinberg1, N Jon Shah1,2
1Medical Imaging Physics, Institute of Neuroscience and Medicine 4 , Forschungszentrum Juelich GmbH, Juelich, Germany; 2Department of Neurology, Faculty of Medicine, RWTH Aachen University, Aachen, Germany
Diffusion Tensor Imaging (DTI) provides access to fibre pathways and structural integrity in the white matter and finds important applications in the clinical practice. Many advanced techniques have been recently suggested for the reconstruction of the diffusion orientation distribution function with an enhanced angular resolution (HARDI). Examination of the sensitivity of the proposed diffusion indices to the underlying microstructure requires a development of the model systems with deliberately tailored properties. The aim of this work was to construct artificial phantoms that are characteristic of sufficiently strong diffusion anisotropy and are suitable for the validation of the analytical models.
1641. Evaluating the Uncertainty of DTI Parameters at 1.5, 3.0 and 7.0 Tesla
Daniel Louis Polders1, Alexander Leemans2, Johannes M. Hoogduin1,3, Jeroen Hendrikse1, Manus Donahue4, Peter R. Luijten1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands; 2Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; 3Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Netherlands; 4Department of Clinical Neurology, University of Oxford, Oxford, United Kingdom
Diffusion Tensor Imaging data acquired at increased field strength shows increased Signal to Noise Ratio. This work compares the uncertainties of DTI-based metrics when scanning at 1.5 3 and 7T. By scanning the same nine volunteers at each field strength, and applying a wild bootstrap method to calculate the uncertainty of the fitted tensors, it is shown that with increasing SNR, the uncertainties for FA and the primary eigenvector decrease.
1642. Validation of Diffusion Tensor Imaging in the Presence of Metal Implants
Felix Schwab1, Bram Stieltjes2, Frederik Bernd Laun3
1Medical Physics in Radiology, Deutsches Krebsforschungszentrum , Heidelberg, Baden Württemberg, Germany; 2Radiology, Deutsches Krebsforschungszentrum, Heidelberg, Germany; 3Medical Physics in Radiology, Deutsches Krebsforschungszentrum, Heidelberg, Baden Württemberg, Germany
The diffusion weighted imaging of the spinal chord is often impeded by metal implants. A quantitative analysis of these effects is performed on a standard titanium implant using phase maps acquired from FLASH sequences and ADC maps acquired from diffusion weighted EPI sequences. The shift δb/b is calculated as a measure of the error. Artefacts caused by the separate parts of the implant are mostly benign and thus diffusion measurements should be feasible if a small distance to the implant is observed.
1643. Within Subject Averaging of Diffusion Tensor MRI Data Sets: A Test-Retest Reproducibility Evaluation
Nico Dario Papinutto1, Jorge Jovicich1
1Center for Mind/Brain Sciences, University of Trento, Mattarello, Trento, Italy
The accuracy and precision of a Diffusion tensor imaging (DTI) acquisition of in-vivo human brains depends on both the acquisition protocol and post-processing used for data analysis. In many cases multiple acquisitions from the same session are averaged to increase signal-to-noise ratio and reduce sensitivity to motion during the acquisition. The complexity of DTI datasets allows for several processing paths to complete eddy current correction, co-registration, averaging and tensor fitting. Here we assess the sensitivity of fractional anisotropy (FA) test-retest reproducibility to different methods for merging multiple within-subject DTI acquisitions.
1644. The Signal Intensity MUST Be Modulated by the Determinant of the Jacobian When Correcting for Eddy Currents in Diffusion MRI
Derek K. Jones1
1CUBRIC, Cardiff University , Cardiff, Wales, United Kingdom
Eddy currents plague diffusion MRI. When they produce a stretch / compression of the image along the phase encode direction, the resultant change in voxel volume leads to a reduction/ increase in signal intensity. Many eddy current correction packages fail to account for this signal change. Here we show that the consequences can be drastic for diffusion tensor MRI, with biases in fibre orientation being as big as 5 degrees in regions of low anisotropy. We conclude that the signal intensity must be modulated by the volumetric change, in order to obtain meaningful and robust results from diffusion MRI.
Lingchih Lin1, Xiaoxu Liu2, Jianhui Zhong3
1Department of Physics and Astronomy , University of Rochester, Rochester, NY, United States; 2Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, United States; 3Department of Imaging Sciences, University of Rochester, Rochester, NY, United States
The analytical relationships of diffusion tensor (DT) derived parameters were compared to quantify the subtle dependent variation between these metrics. This sensitivity evaluation includes the estimation from Monte Carlo simulations and the implementation in a study of five healthy controls and five patients of secondary progressive multiple sclerosis (SPMS). The fractional anisotropy (FA) was simulated as one-dimensional, two-dimensional, and three-dimensional function and reveal distinct properties in different tissue categories. Both white matter (WM) and gray matter (GM) deterioration were observed with decreasing and increasing FA and changes in radial and axial diffusivities in SPMS.
1646. DTI in the Clinic: Evaluating the Effects of Smoothing
Marta Moraschi1, Gisela E. Hagberg2, Giovanni Giulietti1, Margherita Di Paola2, Gianfranco Spalletta2, Bruno Maraviglia3, Federico Giove3
1MARBILAb, Enrico Fermi Center, Rome, Italy; 2Santa Lucia Foundation, Rome, Italy; 3Department of Physics, 'Sapienza' University of Rome, Rome, Italy
We evaluated the effects of smoothing on the outcomes of a Diffusion Tensor Imaging (DTI) voxel-based analyses trying to separate differential effects between patients and controls. Gaussian smoothing introduced a high variability of results in clinical analysis, greatly dependent on the kernel size. On the contrary, anisotropic smoothing proved itself capable of maintaining boundary structures, with only moderate dependence of results on smoothing parameters. Our study suggests that anisotropic smoothing is more suitable in voxel based DTI studies; however, regardless of technique, a moderate level of smoothing seems to be preferable considering the artifacts introduced by this manipulation.
1647. CSF Contamination Correction in DTI Tractography of the Fornix in Elderly Subjects
Sinchai Tsao1, Darryl H. Hwang1, Manbir Singh, 12
1Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States; 2Department of Radiology, University of Southern California, Los Angeles, CA, United States
The microstructural integrity of the limbic regions is frequently compromised in neurodegenerative diseases such as Alzheimer Disease (AD). A key limbic region is the fornix located proximal to the ventricles. Given the relatively large voxel size used in most clinical DTI acquisitions, the probability of CSF contamination in the fornix is high, often leading to interruption of tracts due to either a reduction in FA or misdirection due to erroneous eigenvector estimation, particularly in AD where ventricles are enlarged. FLAIR DTI has been used by many investigators to suppress CSF (e.g. [1,2,3,4]) but at the expense of SNR and data acquisition time and to our knowledge, FLAIR DTI is rarely used in clinical studies. Aiming toward eventual quantification of DTI metrics such as FA and tract density in the fornix and other limbic pathways in AD, the objective of this work was to develop a post-processing strategy to correct partial volume effects such that it could be used to analyze existing clinical DTI data.
1648. SPM Normalisation Toolbox for Diffusion Weighted Images
Volkmar H. Glauche1, Siawoosh Mohammadi2, Michael Deppe2
1Department of Neurology, University Hospital Freiburg, Freiburg, Germany; 2Department of Neurology, University of Muenster, Germany
The toolbox implements normalisation strategies to prepare data for VBM-style voxel-based statistics of FA images (FA-VBS) in SPM. It provides a convenient interface to spatially normalise DWI datasets even if no additional anatomical images are available. It integrates tightly into the SPM8 batch system within the Diffusion Toolbox. The resulting normalised images can be used for voxelwise or multivariate analyses in any of the common analysis packages for VBM. This toolbox may therefore help to standardize the FA-VBS normalisation step.
1649. Cerebrospinal Fluid as an Internal Quality Control Marker
Ryan J. Bosca1,2, A.J. Kumar1, Jihong Wang1
1The University of Texas M.D. Anderson Cancer Center, Houston, TX, United States; 2The University of Texas Graduate School of Biomedical Sciences, Houston, TX, United States
Cerebrospinal fluid (CSF) is a good candidate for an internal quality control marker of diffusion tensor imaging because the diffusion properties should be close to known values and show little variation over time. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) for 174 DTI (111 at 1.5T, 63 at 3.0T) studies for 20 patients were measured. Coefficients of variation were calculated for all studies at 1.5T (4.2%, 14.2%) and 3.0T (6.2%, 19.7%) for ADC and FA values, respectively. Small variations in the ADC were observed indicating CSF as a promising candidate for an internal quality control marker.
1650. Fully Automatic Postprocessing and Evaluation of DTI Data: Unsupervised Pipeline for Batch Jobs
Kurt Hermann Bockhorst1, Cheukkai K. Hui1, Ponnada A. Narayana1
1DII, University of Texas, Houston, TX, United States
We created a batch process which refines raw DTI data; it reduces ghosts and filters noise, strips extramenigeal tissue and registered to an atlas, which we created from high resolution DTI data to avoid mis-registration with spin-echo derived data. 3D-masks of 17 brain structures were created to facilitate automatic evaluation of the data.
1651. Repeatability of Mono- And Bi-Exponentially Modelled Diffusion at 3 Tesla
Peter Gibbs1, Martin D. Pickles1, Lindsay W. Turnbull1
1Centre for MR Investigations, University of Hull, Hull, East Yorkshire, United Kingdom
Recent work has demonstrated that it is technically possible to acquire DWI data with low b-values to quantify the ‘perfusive’ fraction of the ADC decay curve via bi-exponential modelling. This work seeks to assess the repeatability of such modelling and the dependence on accurate b-value implementation by system manufacturers. A repeatability of 21% for mono-exponential fitting indicates its efficacy for monitoring treatment induced changes. Bi-exponential fitting is found to be less repeatable, especially the ‘perfusive’ fraction parameter.
1652. High-Resolution Diffusion Tensor Imaging (DTI) of the Human Head at 7T: First Results with a 70 MT/m Whole Body Gradient System
Ralf Luetzkendorf1, Oliver Speck2, John Grinstead3, Joerg Stadler4, Johannes Bernarding1
1Department for Biometry and Medical Informatics, OvG University Magdeburg, Magdeburg, Saxony Anhalt, Germany; 2Biomedical Magnetic Resonance, OvG University Magdeburg, Magdeburg, Germany; 3Siemens Medical Solutions USA, Inc; 4Leibniz Institute for Neurobiology
High resolution DTI at ultra-high fields is advantageous as the initially higher signal-to-noise ratio allows to increase the resolution while simultaneously counteracting the according signal losses. Stronger gradients will also enable to apply larger diffusion-weighting at still acceptable TE times. We aimed to reduce TE to overcome the disadvantages of ultra high field conditions such as increased distortions and shortened T2 values. To this purpose we used a new 70 mT/m whole body gradient system for a 7T MR scanner and an improved DTI sequence with a single refocusing pulse to acquire isotropic DTI images with a resolution of (1.4 mm) 3.
Hermien E. Kan1, Matthias J.P. van Osch1, Maarten J. Versluis1, Aranee Techawiboonwong2, Dinesh K. Deelchand3, Pierre G. Henry3, M Marjanska3, Mark A. van Buchem1, Andrew G. Webb1, Itamar Ronen, 12
1C.J. Gorter Center, department of radiology, Leiden University Medical Center, Leiden, Netherlands; 2Radiology, Boston University, Boston, United States; 3Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States
Assessment of diffusive properties of metabolites using diffusion weighted spectroscopy has so far been, in humans, limited to the brain metabolites N-acetyl aspartate, creatine and phosphocreatine and choline. To further assess substructural differences, it would be advantageous to also study ADCs of other metabolites, like myo-inositol, glutamate and glutamine. In this study, we obtained ADC values of these metabolites in human grey and white matter, and observed that in grey matter overall ADCs were lower compared to white matter with a significantly reduced glutamate. This is in agreement with observations in monkeys, and indicates increased diffusion restriction in grey matter.
Emily Turner Wood1,2, Daniel S. Reich2,3, Jonathan A. Farrell3,4, Joseph S. Gillen4, Peter B. Barker3, Itamar Ronen5
1Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 2NeuroImmunology Branch (NINDS), National Institutes of Health, Bethesda, MD, United States; 3Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 4F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States; 5Leiden University Medical Center, Leiden, Netherlands
Diffusion tensor spectroscopy (DTS) combines features of DTI and spectroscopy to provide information about the diffusion of intracellular metabolites and therefore specific information about tissue microstructure and health. We compare the diffusion properties of N-acetylaspartate (NAA) and water at two locations in the corpus callosum at 7T. Subjects were scanned at 7T with a 32-channel head coil using a DTS sequence that incorporated bipolar diffusion gradients within a point-resolved spectroscopic (PRESS) sequence. We demonstrate high resolution spectra and diffusion values consistent with previous reports at lower fields, demonstrating the feasibility of DTS at 7T to quantify a range of metabolites.
1655. Language Lateralization Explained by the Generalized Fractional Anisotropy in the Auditory Nerve and the Corpus Collosum as Studied Using Diffusion Spectrum Imaging Tractography and FMRI
Kayako Matsuo1, Yu-Chun Lo2, Fang-Cheng Yeh3, Yi-Huan Wu4, Shen-Hsing Annabel Chen5, Wen-Yih Isaac Tseng1
1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; 3Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States; 4Department of Medicine, National Taiwan University, Taipei, Taiwan; 5Division of Psychology, School of Humanities and Social Sciences, Nanyang Technological University, Singapore
We measured the generalized fractional anisotropy (GFA) of the auditory nerve (AN) to bilateral Heschl's gyri via the corpus callosum (CC) using diffusion spectrum imaging (DSI). The individual language asymmetry was determined using fMRI. The left lateralized AN was found to be related to the leftward language asymmetry. The mild lateralization in the AN as well as the lower GFA in the CC tend to have relationship with the bilateral language function. The findings provide plausible evidence for the degree of conductivity of the AN as well as the CC in determining language lateralization/asymmetry between the hemispheres.
1656. Performance of Deterministic and Probabilistic Diffusion Tensor and Q-Ball Corticospinal Tractography in Brain Tumor Patients
Monica Bucci1, Maria Luisa Mandelli2, Jeffrey I. Berman, Bagrat Amirbekian3,4, Christopher Nguyen, Mitchel S. Berger5, Roland G. Henry
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States; 2Department of Neuroradiology, Istituto Neurologico Carlo Besta, Milano, Italy; 3Radiology and Biomedical Imaging, University of California, San Francisco; 4UC Berkeley and UCSF Graduate Program in Bioengineering; 5Department of Neurological Surgery, University of California San Francisco
There are different methods available for fiber tracking but only with few methods it is possible to quantify the accuracy and precision in clinical applications. We used preoperative HARDI data from patients with cerebral glioma to obtain corticospinal fiber tracts with deterministic and probabilistic Diffusion Tensor and Q-Ball fiber tracking algorithms using cortical and subcortical stimulation sites from IES as gold standard. The functional motor sites allows determination of the false negative rate of connectivity, which reflects the accuracy of the tractograms. The subcortical stimulation sites enable determination of the accuracy and precision of the course of the predicted CST.
1657. Diffusion Tensor Imaging of Basal Ganglia Output Fibers
Mihaela Onu1, Uta Nicola Sboto-Frankenstein2, Patricia Gervai2, Greg Molnar3, Boguslaw Tomanek2
1Biophysics, University of Medicine "Carol Davila", Bucharest, Romania; 2National Research Council Institute for Biodiagnostics; 3Medtronic Inc.
The current study was designed to investigate if it is feasible to use MRI Diffusion Tensor Imaging to visualize basal ganglia output fibers, in particular the Ansa Lenticularis (AL) and Lenticular Fasciculus (LF). Using the Globus Pallidus Internus (GPi) as a seed point, two fiber branches were identified. One originated in the dorsal aspect of the GPi and the second in the ventral aspect of the GPi. These two tracts may be indicative for the localization of the LF and AL respectively.
1658. Asymmetric Structural Connectivity of Default-Mode Network : An Integrated Study of FMRI and Probabilistic DTI
Tzu-chen Yeh1, Chou-Ming Cheng1, Zong-Kai Hsu2, Jen-Chuen Hsieh2, Low-Ton Ho1
1Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan, Taiwan; 2Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan, Taiwan
The spatial template of default-mode network (DMN) of sixty normal subjects has been constructed as five regions of interest (ROIs) as precuneus/posterior cingulate areas with the highest reproducibility. Multimodal approaches using BOLD-based fMRI and probabilistic DTI (pDTI) demonstrated the limited structural connectivity within each ROI within DMN correlates. By penetration maps of pDTI in twenty-two normal subjects, asymmetry of bilateral cingulum cortices implied preference of right posterior medial parietal regions for interpretation of internal/external environment with concert action of medial prefrontal areas, as one of the potential functions of DMN.
1659. Language Circuits of Human Brain: An Integrated Study of FMRI and Probabilistic DTI
Zong-Kai Hsu1, Tzu-Chen Yeh2,3, Chou-Ming Cheng2, Wen-Jui Kuo4, Jen-Chuen Hsieh5
1Institute of Brain Science , National Yang Ming University , Taipei, Taiwan; 2Laboratory of Integrated Brain Research, Department of Medical Research & Education, Taipei Veterans General Hospital, Taipei, Taiwan; 3Institute of Brain Science , National Yang Ming University, Taipei, Taiwan; 4Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan; 5Institute of Brain Science, National Yang Ming University, Taipei, Taiwan
The language anatomical model proposed that Broca¡¦s area located in the inferior frontal lobe and Wernicke¡¦s area located in the superior temporal gyrus were connected through the arcuate fasciculus (AF). Hickok and Poeppel  and others recently proposed a dual stream model for auditory language processing. From the superior temporal gyrus, which is engaged in early cortical stages of speech perception, the system diverges into two processing streams. The aim of this study is to examine the language circuits of the dual stream model using visual perception by an integrated functional MRI (fMRI) and probabilistic diffusion tensor imaging (pDTI) method.
1660. Resolution-Dependent Differences in Fiber Tracking and Quantification of the Visual Pathways
Jan Klein1, Peter Erhard2, Horst Karl Hahn1
1Fraunhofer MEVIS, Bremen, Germany; 2FB 2 (Chemistry) and Center of Advanced Imaging (CAI), Germany
Fiber tracking and quantification of the visual pathways is still a challenging problem due distortions in the vicinity of the optic nerve, the small diameter of the bundle itself, crossing fibers in the optic chiasm and the capsula interna, the high curvature in the Meyers loop, and the discontinuity in the corpus geniculatum laterale. We examine how changes in the resolution of the DTI data sets influence the fiber tracking and quantification of the visual pathways, and show that an anisotropic resolution with a high coronal in-plane resolution should be preferred to an isotropic resolution with the same volume per voxel.
1661. Characterization of White Matter Fasciculi with T1 Quantification: A Feasibility Study at High Field
Nico Dario Papinutto1, Jorge Jovicich1
1Center for Mind/Brain Sciences, University of Trento, Mattarello, Trento, Italy
Diffusion tensor imaging (DTI) of in-vivo human brains is a technique that is becoming widely used to get insight into normal and abnormal white matter anatomical connectivity. Characterization of pathologies with fractional anisotropy (FA) losses have been done, both at voxel level and along tracts. A promising method to further improve the characterization of main streamlines consists on adding relaxation times measurements. We present a simple method for T1 quantification of white matter tracts using sequences available in most commercial scanners.
1662. Gradual Variation of Anatomical Connectivity in the Macaque Insula Revealed by Probabilistic Tractography
Leonardo Cerliani1, Helen D'Arceuil2, Rajat M. Thomas3, Saad Jbabdi4, Christian M. Keysers1
1Neuroscience, University Medical Center Groningen, Neuroimaging Center, Groningen, Netherlands; 2Dept. of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, United States; 3Kapteyn Astronomical Institute, University of Groningen, Netherlands; 4FMRIB Centre, Univ. of Oxford, John Radcliffe Hospital, United Kingdom
The connectivity of the macaque insula was analyzed by means of probabilistic tractography on diffusion-weighted images. The main aim was to detect and analyze trajectories of connectivity variation in this brain region, and to test the consistency of the results with the available anatomical evidence from animal literature. The employed method of laplacian eigenmaps was able to recover the expected gradual change in connectivity, and to discriminate this with the sharp transition in connectivity featured by the medial motor cortex
Kerstin Pannek1,2, Jane Mathias3, James Taylor4, Parnesh Raniga5, Olivier Salvado5, Stephen Rose1,2
1Centre for Magnetic Resonance, University of Queensland, Brisbane, Queensland, Australia; 2UQ Centre for Clinical Research, University of Queensland, Brisbane, Queensland, Australia; 3School of Psychology, University of Adelaide, Adelaide, South Australia, Australia; 4Magnetic Resonance Imaging Unit, Royal Adelaide Hospital, Adelaide, South Australia, Australia; 5The Australian E-Health Research Centre, CSIRO, Brisbane, Queensland, Australia
Structural connectivity of the brain using MR diffusion tractography has gained significant interest. A connectivity matrix of cortical connectivity may provide unique insight into brain organisation. We aimed to develop a method to determine the number of seeds required to obtain stable and reproducible connectivity, and to assess reproducibility over time. We employ a bootstrap approach for estimation of these parameters. While connectivity measures of some regions are highly reproducible over time, other connections show poor reproducibility. This study highlights the relationship between seed number and reproducibility of connectivity.
1664. Validation of in Vivo Mouse Brain Fiber Tracking with Correlative Axonal Tracing in Wild-Type and Reeler Animals
Laura-Adela Harsan1, Csaba David2, Marco Reisert1, Susanne Schnell1, Jürgen Hennig1, Dominik von Elverfeldt1, Jochen F. Staiger2
1Department of Diagnostic Radiology, Medical Physics, University Hospital, Freiburg, Germany; 2Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Freiburg, Germany
The present study validates an in-vivo DT-MRI and FT protocol capable of identifying and characterizing the subtle connection pathways in the living mouse brain. The reconstructions of the thalamocortical projections derived from in-vivo DT-MRI were co-registered and correlated with 3D reconstructions of the fibers labeled with Phaseolus vulgaris-leucoagglutinin histological tracer, injected in the thalamus of the same animal. Good agreement between the deterministic and probabilistic tractography and the histological tracing was obtained in wild type and reeler mutant brains
1665. Challenges of Cortical Connectivity Measurements Using MR Tractography
Ann Sunah Choe1,2, Yurui Gao1,3, Iwona Stepniewska4, Xia Li5, Zhaohua Ding5, Adam W. Anderson1,3
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States; 2Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; 3Vanderbilt University Institute of Imaging Science , Vanderbilt University, Nashville, TN, United States; 4Department of Psychology, Vanderbilt University, Nashville, TN, United States; 5Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States
Study of anatomical connections often involves tracing fiber bundles to and from cortical areas of interest. The fiber tracking involved in such studies presents some unique problems. One of the challenges is the low diffusion anisotropy in gray matter, and the high directional uncertainty this causes. This problem is often circumvented by placing seed regions within the subcortical white matter, below the target regions of cortex. This approach risks tracking erroneous fibers due to limited spatial resolution and the complex interface between white and gray matter. In this abstract, the risk of such approaches is demonstrated by comparing DTI fiber pathways to histological sections of the corresponding regions.
Chris James Rose1,2, David Morris1,2, Hamied Haroon1,2, Karl Embleton, 2,3, Nikos Logothetis1,4, Matthew Lambon Ralph3, Geoffrey J. Parker1,2
1Imaging Science and Biomedical Engineering, The University of Manchester, Manchester, United Kingdom; 2The University of Manchester Biomedical Imaging Institute, Manchester, United Kingdom; 3School of Psychological Sciences, The University of Manchester, Manchester, United Kingdom; 4Max Planck Institute for Biological Cybernetics, Tübingen, Germany
We present version 2.0 of piconmat.com, a freely-available web-based system for exploring connectivity strengths between cortical and subcortical regions in a database of individuals. Connectivity strength is computed using diffusion MRI and probabilistic tractography. Version 2.0 is a significant update: connectivity strengths are presented in an interactive connectivity matrix and controls allow the user to study connectivity in individuals who meet certain criteria (e.g., right-handed males aged 25-50), and connectivity strengths for individuals belonging to different groups can be visually and quantitatively compared (e.g., right-handed males vs. females).
1667. Diffusion MRI and Anatomical Tracer Tractography of Association Pathways in the Same Brain
Jennifer Campbell1, Ilana R. Leppert1, Stephen Frey2, Michael Petrides2, G. Bruce Pike1
1McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada; 2Cognitive Neuroscience Unit, Montreal Neurological Institute, McGill University
Reliable in vivo diffusion MRI fibre tractography, particularly in association pathways, remains a difficult task due to a mismatch between the tract size and the image resolution achievable in a reasonable scan time. The objective of this study was to perform both diffusion MRI tractography and traditional tracer injection tract tracing in the association pathways of the same rhesus macaque monkey. Evaluation of diffusion MRI tract tracing in these association pathways can give us insight into its feasibility for mapping subtle connectivity in the human brain.
1668. Estimation of the Uncertainty of Diffusion MRI Fiber Tracking Parameters with Residual Bootstrap
Christopher Tam Nguyen1, SungWon Chung2, Jeffrey I. Berman1, Roland G. Henry1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States; 2Radiology, Brigham and Women's Hospital, Harvard University, Boston, MA, United States
Fiber tracking (FT) based on diffusion MR has important applications for structural connectivity analyses of brain diseases and pre-operative FT of the brain. The residual bootstrap (RB) analysis on voxelwise DTI parameters is not appropriate to characterize the uncertainty in the large 3D regions defined by FT. Therefore, we will illustrate the appropriate implementation of RB to obtain the uncertainty of fiber tracking parameters (FTPs) such as number of streamlines (NOS). We validated our method with a Monte Carlo simulation showing that RB accurately estimated the SE of the NOS.
1669. Quantitative Improvement of Diffusion Spectrum Imaging Tractography Using Statistical Denoising
Li-Wei Kuo1, Justin P. Haldar2, Yu-Chun Lo3, Cheng-Liang Liu1, Zhi-Pei Liang2, Wen-Yih Isaac Tseng1,4
1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2Department of Electrical and Computer Engineering, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States; 3Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan; 4Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan
Noise contamination is a significant problem in diffusion spectrum imaging (DSI) tractography, and previous work has proposed a statistical denoising algorithm to mitigate the effects of low signal-to-noise ratio. In this work, improvements to fiber orientation accuracy due to denoising were quantified using a systematic analysis of angular precision and dispersion metrics. Results show that the proposed denoising method significantly improves angular precision and dispersion. Furthermore, the tractography results demonstrate better reconstruction of white-matter structures using the denoised data. Future work will use the proposed denoising algorithm to improve spatial resolution and reduce scan time.
1670. Improved Probabilistic Streamlines Tractography by 2nd Order Integration Over Fibre Orientation Distributions
J-Donald Tournier1,2, Fernando Calamante1,2, Alan Connelly1,2
1Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Victoria, Australia; 2Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
Probabilistic streamlines algorithms are amongst the most promising methods for fibre-tracking, but are potentially subject to a number of deficiencies. These include a tendency to overshoot in highly curved regions, and to switch directions in crossing fibre regions. To address both of these issues, we propose a higher-order probabilistic streamlines algorithm, based on 2nd order integration over fibre orientation distributions (iFOD2), with a computational complexity similar to current first order methods. We demonstrate the advantages of the proposed iFOD2 algorithm on simulated data, and apply the method to in-vivo data.
1671. Tract-Based Parameterization of Local White Matter Geometry
Peter Savadjiev1, Marek Kubicki1, Sylvain Bouix1, Gordon L. Kindlmann2, Martha E. Shenton1,3, Carl-Fredrik Westin4
1Psychiatry, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States; 2Computer Science, University of Chicago, Chicago, IL, United States; 3Psychiatry, VA Boston Healthcare System, , Brockton , MA, United States; 4Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States
Knowledge of fibre geometry and its variation along fibre tracts can be useful for the study of normal and pathological white matter. In this work we present a tract-based analysis of two recently introduced measures of fibre geometry, which compute fibre dispersion and fibre curving, directly from a diffusion tensor field and its gradient. These measures of fibre geometry are mapped and analysed along a parametric representation of fibre tracts. Such representations of fibre tract geometry are an important tool for the understanding of white matter structure.
1672. Towards Image-Dependent Safety Hulls for Fiber Tracking
Sebastiano Barbieri1, Jan Klein1, Christopher Nimsky2, Horst K. Hahn1
1Fraunhofer MEVIS - Institute for Medical Image Computing, Bremen, Germany; 2Department of Neurosurgery, University Marburg, Marburg, Germany
We make use of a DTI software model in order to systematically analyze the influence of noise, fiber bundle diameter, number of seed points and tensor anisotropy on the magnitude of fiber tracking errors. In our model we simulate image noise and partial volume artifacts. As a measure for fiber tracking errors we introduce a so called "safety radius". The safety radius is used to construct safety hulls, which are tubes that surround the tracked fibers and indicate their margin of error. We further analyze how fibers are spatially distributed inside a cylindrical fiber bundle during the tracking process.
Yajing Zhang1, Kenichi Oishi2, Michael I. Miller3, Jiangyang Zhang4, Susumu Mori2,5
1Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 2Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 3Center for Imaging Science, Johns Hopkins University, Baltimore, MD, United States; 4Radiology and Radiological Science, , Johns Hopkins University School of Medicine, Baltimore, MD, United States; 5F.M.Kirby Resarch Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
We performed comprehensive studies of human white matter anatomy using a novel atlas based automated fiber tracking system. 130 3-D ROIs were transformed from our brain atlas to the individual subject using non-linear transformations and used for automated fiber tracking. This approach allows exhaustive search of white matter bundles that consistently exist in the normal population. The method was validated by comparing to manual results by experts. We identified 29 short cortico-cortical association fibers in addition to well-defined major bundles. Probabilistic maps of such tracts in normalized space were constructed for the first time in the normal population.
1674. Global Fiber Tracking Becomes Practical
Marco Reisert1, Irina Mader2, Constantin Anastasopoulus2, Susanne Schnell1, Valerij Kiselev1
1Medical Physics, University Hospital Freiburg, Freiburg, Baden-Wuerttemberg, Germany; 2Section of Neuroradiology, University Hospital Freiburg
Local fiber tracking approaches are based on the 'walker' principle, the fibres are reconstructed path-by-path by small successive steps along the tracts. On the other hand global ideas try to reconstruct all fibres at once by optimizing a certain global objective. Local algorithms are fast but suffer from accumulated errors. Global methods have a more sound foundation but are very complex to optimize. This abstract presents an approach, which fuses both ideas while keeping their advantages. The experiments show that the approach is orders of magnitude faster than recent global approaches while improving the detection performance.
1675. Probabilistic Connectivity in Fibre Tractography
Parya MomayyezSiahkal1, Kaleem Siddiqi1
1School of Computer Science, Centre for Intelligent Machines, McGill University, Montréal, Quebec, Canada
We introduce a probabilistic connectivity index between two regions, based on diffusion MRI, by using a stochastic nonlinear differential equation to model the Brownian motion of water molecules in a medium. The model is linked to the physical basis of the diffusion process and leads to promising results on the MICCAI 2008 Fibre cup phantom. Our experiments yield highly curving fibre tracts without the need to impose thresholds on curvature or torsion or to eliminate false positives. An additional benefit is the algorithm's low computational complexity and the fact that its parameters are data-driven and are selected automatically.
1676. Analysis of Connectivity of Gray Matter Regions Using DTI and Graph Theory
Amy Kuceyeski1, Ashish Raj1
1Radiology, Weill Cornell Medical College, New York, NY, United States
The connectivity of gray matter regions in the brain via white matter tracts has recently become an area of wide interest due to the advances in imaging techniques that measure structural connections via white matter (DTI. The information that can be extracted from this modality has not yet been harvested fully due to its relative novelty; however some studies have proven its potential. We propose a computational methodology that utilizes DTI and structural images of the brain, graph theory, and clustering algorithms to explore regions of high connectivity and importance to overall connectivity in normal brains.
Eizou Umezawa1, Yoshifumi Kuwayama2, Akihito Yamamoto2, Hikaru Masumoto2, Takashi Fukuba2, Masao Ohashi2, Keiko Terada2, Toshiaki Mori2, Yutaka Kinomura2, Kojiro Yamaguchi1, Masayuki Yamada1, Hirofumi Anno1, Kazuhiro Katada3
1School of Health Sciences, Fujita Health University, Toyoake, Aichi, Japan; 2Radiological Division, Fujita Health University Hospital, Toyoake, Aichi, Japan; 3Department of Radiology, School of Medicine, Fujita Health University, Toyoake, Aichi, Japan
Multi-Shelled QBI (MS-QBI) gives a new orientation distribution function based on the moment of the probability density function. We perform the fiber tracking of human brain based on MS-QBI and confirm the practicability of the method. We implement a simple procedure for streamline fiber trackings of pathways that encounter crossings. The pyramidal tract (PT) can be traced beyond the crossing with the superior longitudinal fasciculus by MS-QBI. The distinction between PT and the corpus callosum in the corona radiata is still difficult.
1678. Effects of Susceptibility Distortion and Phase Encoding Direction on Tract Consistency in Diffusion Tensor Imaging
Mustafa Okan Irfanoglu1,2, Lindsay Walker2, Carlo Pierpaoli2
1Department of Radiology, The Ohio State University, Columbus, OH, United States; 2NICHD, National Institutes of Health, Bethesda, MD, United States
The distortions on phase-encoding direction of diffusion weighted images due to magnetic susceptibility and concomitant fields greatly affect the quality and consistency of tractography using on diffusion sequences. In this work, data from a healthy population were acquired in both Right-Left and Anterior-Posterior phase encoding directions and the effects of these distortions and EPI distortion correction were analyzed on specific fiber bundles. Results indicate tracts are greatly affected by these distortions and consistency and quality of the tracts are improved with correction and that this correction process should be part of typical diffusion sequences acquired for tractography purposes.
1679. On the Importance of Appropriate Fibre Population Selection in Diffusion Tractography
Jonathan D. Clayden1, Chris A. Clark1
1Institute of Child Health, University College London, London, Greater London, United Kingdom
While a lot of recent research in diffusion MRI has focussed on estimating the orientations of multiple fibre populations within image voxels, little attention has been given to the problem of how to effectively use this information in tractography. Typically a tractography algorithm selects a fibre direction to follow based on continuity, but we show here that a alternative approach based on prior knowledge gives substantially more robust results. Our technique is fully automated and uses a reference tract to inform the process.
1680. Quantitative Comparison of Automatic and Manual Tract Segmentation Methods
Susana Muñoz Maniega1, James D. Bridson2, Wei Jie Jensen Ang2, Paul A. Armitage1, Catherine Murray3, Alan J. Gow3, Mark E. Bastin4, Ian J. Deary3, Joanna M. Wardlaw1
1Clinical Neurosciences, University of Edinburgh, Edinburgh, United Kingdom; 2Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom; 3Psychology, University of Edinburgh, Edinburgh, United Kingdom; 4Medical Physics, University of Edinburgh, Edinburgh, United Kingdom
We compare probabilistic neighbourhood tractography (PNT), an automatic tract segmentation method, with a well accepted tractography method using manual seed placement and multiple region-of-interest (ROI) constraints. Tracts were segmented in the same data set using both methods and mean values of FA and MD compared. Mean differences between PNT and ROI methods were ≤10%, comparable with the reproducibility obtained when ROI are manually placed by different operators. PNT segmentation showed a reasonable agreement with the more conventional ROI tract segmentation method, with the advantage of removing operator dependency.
1681. A New Combined Distance Measure for the Clustering of Fiber Tracts in Diffusion Tensor Imaging (DTI)
Christian Ros1, Daniel Güllmar1, Juergen R. Reichenbach1
1Medical Physics Group, Institute for Diagnostic and Interventional Radiology, Jena University Hospital, Jena, Germany, Jena, Thuringia, Germany
In recent years various fiber tractography methods have been evolved. Although these resulting tractograms offers plenty of information, they are rarely used in clinical routine due to the fact that processing is often time-consuming and an experienced operator is essential to obtain good results. To overcome this limitations cluster analysis can be employed to partition fiber tracts into clusters through comparison of tract-specific features or similarity measures. The aim of this study was to develop a new combined similarity measure that combines a shape based distance measure with other distance measures.
1682. Visualizing and Exploring Tractograms Via Two-Dimensional Connectivity Maps
Radu Jianu1, Cagatay Demiralp1, David H. Laidlaw1
1Brown University, Providence, RI, United States
We introduce a circular graph visualization of tract projections in a framework that uses two-dimensional map representations for exploring connectivity in the brain. Expert feedback indicates that it can be useful for understanding connectivity densities and configurations.
1683. Visualization of Intrarenal Water Transport by Diffusion Tensor Tractography
Michael Pedersen1, Anders B. Lødrup1, Kristian Karstoft1, Eva A. Nielsen2, Mette K. Hagensen2, Peter A. Nielsen2, Andreas Stavropoulos3, Bente Jespersen4, Steffen Ringgaard1, Morten Smerup2
1MR Research Center, Aarhus University Hosptial, Aarhus, Denmark; 2Institute of Clinical Medicine, Aarhus University Hosptial, Aarhus, Denmark; 3Dept. of Periodontology, Aarhus University, Aarhus, Denmark; 4Department of Nephrology, Aarhus University Hospital, Aarhus, Denmark
The aim of this study is to investigate if DTI can be used for imaging the principal route of free water in the kidney, and we hypothesize that this route can act as an indirect representation of the segments of nephrons going centripetally from the renal parenchyma to the collecting ducts. The orientation of medullary diffusion anisotrophy was visualized using a proposed DTI tractography method
1684. A Monte-Carlo Approach for Estimating White Matter Density in HARDI Diffusion Data
Parnesh Raniga1, Kerstin Pannek2,3, Jurgen Fripp1, David Raffelt1, Pierrick Bourgeat1, Oscar Acosta1, Donald Tournier4, Allan Connelly4, Stephen Rose2,3, Olivier Salvado1
1CSIRO Preventative Health National Research Flagship ICTC, The Australian e-Health Research Centre, Brisbane, Queensland, Australia; 2Centre for Magnetic Resonance, University of Queensland, Brisbane, Queensland, Australia; 3UQ Centre for Clinical Research, University of Queensland, Brisbane, Queensland, Australia; 4Brain Research Institute, Melbourne, Victoria, Australia
The abstract is about using visitation maps to perform quantitative analysis.
1685. On the Behavior of DTI and Q-Ball Derived Anisotropy Indices
Klaus H. Fritzsche1, Bram Stieltjes2, Frederik B. Laun3, Hans-Peter Meinzer1
1Division of Medical and Biological Informatics, German Cancer Research Center, Heidelberg, B-W, Germany; 2Division of Radiology, German Cancer Research Center; 3Division of Medical Physics, German Cancer Research Center
Anisotropy indices in diffusion imaging have never been systematically analyzed under conditions of heterogeneous fiber configurations. Furthermore, q-ball imaging indices have so far not been evaluated with respect to accuracy, precision, b-value dependency and contrast-to-noise ratio (CNR). This study performed a systematic analysis using Monte Carlo simulations and measurements in crossing fiber phantoms. The GFA (reconstructed with solid angle consideration) showed the lowest dependency on b-value and the best results regarding accuracy and precision. Its behavior in crossing fiber voxels was also preferable. Main drawback was its low CNR, especially in low anisotropy fibers.
1686. Analytical Q-Ball Imaging with Optimal λ-Regularization
Maxime Descoteaux1, Cheng Guan Koay2, Peter J. Basser2, Rachid Deriche3
1Computer Science, Université de Sherbrooke, Sherbrooke, Québec, Canada; 2National Institute of Child Health and Human Development, Bethesda, MD, United States; 3INRIA Sophia Antipolis - Méditerranée, Sophia Antipolis, France
We present analytical q-ball imaging with optimal Generalized Cross Validation (GCV)-based regularization. The method is the optimal extension of the standard analytical q-ball imaging, normally implemented using a fixed regularization λ = 0.006. QBI with optimal λ shows a distinct advantage in generalized fractional anisotropy (GFA) computation when the underlying structure is complex and in single fiber parts of real data.
Jelle Veraart1, Wim Van Hecke2,3, Dirk Poot1, Ines Blockx4, Annemie Van Der Linden4, Marleen Verhoye4, Jan Sijbers1
1Vision Lab, University of Antwerp, Antwerp, Belgium; 2Department of Radiology, Antwerp University Hospital, Antwerp, Belgium; 3Department of Radiology, University Hospitals of the Catholic University of Leuven, Leuven, Belgium; 4Bio Imaging Lab, University of Antwerp, Antwerp, Belgium
Due to the presence of complex cellular microstructures in the brains’ white matter, the diffusion weighted signal attenuation with respect to the b-value can not accurately be approximated by the monoexponential function assumed by DTI. Because of this, the estimation of the diffusion coefficient and the associated diffusion parameters depend on the b-value of the acquisition. The recently proposed higher order DKI model fits the signal attenuation more properly as a result of which, as demonstrated in this study, a more accurate estimation of the diffusion parameters is obtained. In addition the parameter estimation appears b-value independent.
1688. Anomalous Diffusion Tensor Imaging
Matt G. Hall1, Thomas Richard Barrick2
1Dept of Computer Science, University College London, London, United Kingdom; 2Centre for Clinical Neuroscience, Division of Cardiac & Vasculas Sciences, St Georges, University of London, London, United Kingdom
The theory of anomalous diffusion applied to diffusion imaging predicts a stretched-exponential form for the decay of diffusion-weighted signal with b-value. We generalise this to consider diretional anisotropy of the parameters of the stretched-exponential form. The resulting technique (anomalous diffusion tensor imaging) provides estimates of tensors describing diffusivity and tissue heteroegeneity in each scan voxel. We apprly the technique to healthy in vivo data and use the resulting tensors to infer tissue microstructure perform streamline tractography in the corpus callosum.
1689. Spectral Decomposition of a 4-Rank Tensor and Applications to Generalised Diffusion Tensor Imaging
Marta Morgado Correia1,2, Guy B. Williams2
1MRC Cognition and Brain Sciences Unit, Cambridge, Cambridgeshire, United Kingdom; 2Wolfson Brain Imaging Centre, Cambridge, Cambridgeshire, United Kingdom
In this work we show how spectral decomposition of a 4-rank generalised diffusion tensor can be used to characterise brain structure, including the definition of two metrics of anisotropy that do not depend on the arbitrary choice of a normalising function and its parameters.
1690. An Accelerated, Alternative Approach for Estimating Zero-Displacement Probability in Hybrid Diffusion Imaging
A P. Hosseinbor1, J O. Fleming2, Y-C Wu3, A A. Samsonov4, A L. Alexander
1Medical Physics, University of Wisconsin-Madison, Madison, WI, United States; 2Neurology, University of Wisconsin-Madison; 3Dartmouth College; 4Radiology, University of Wisconsin-Madison
In HYDI, Po is conventionally estimated by using signal measurements in all shells (Poall), which requires long scan time. However, the highest diffusion-weighting measurements are likely to contribute most heavily to restricted diffusion (RD) signal. Thus, an alternative, faster approach for characterizing RD would be to use signal measurements only in outermost shell (Poouter). In this work, we compare both Poall and Poouter approaches in NAWM from MS patients and WM in a control group. We show that both approaches yield similar statistical properties for characterizing RD, which suggests Poouter is both adequate and faster than using full q-space measurements.
1691. Combined DTI/HARDI Visualization
Vesna Prckovska1, Tim H.J.M. Peeters1, Markus van Almsick1, Anna Vilanova1, Bart ter Haar Romeny1
1Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands
We present a novel visualization framework that unifies the models from DTI and HARDI, using a classification scheme for model selection. The data is represented by diffusion tensors or fibers in the Gaussian and HARDI glyphs in the non-Gaussian areas. We exploit the capabilities of modern GPU to optimize the rendering performance and visual quality of the glyphs. All of the visualization parameters are controlled by the user in real time. Different color coding on the glyphs enhance the anisotropy information or highlight maxima. This is the first attempt to give fast and intuitive insight into the complex HARDI data.
1692. Determination of Local Fibre Configuration Using Bayesian Neighbourhood Tract Modeling
Thomas Glyn Close1,2, Jacques-Donald Tournier1,3, Fernando Calamante1,3, Leigh A. Johnston2,4, Iven Mareels2, Alan Connelly1,3
1Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Victoria, Australia; 2School of Engineering and NICTA VRL, University of Melbourne, Melbourne, Victoria, Australia; 3Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia; 4Howard Florey Insitute, Florey Neuroscience Institutes (Parkville), Melbourne, Victoria, Australia
We present a new method for characterising white matter fibre configurations within local neighbourhoods. Instead of single-voxel based models of fibre orientations represent the complete tract configuration within a local neighbourhood (eg. 3x3x3 voxels) via a rich tract-segment model. By fitting multiple tracts simultaneously, this approach utilizes the probability of surrounding tracts to improve the fit of each tract.
1693. Diffusion Gradient Calibration Influences the Accuracy of Fibre Orientation Density Function Estimation: Validation by Efficiency Measure
Yuliya Kupriyanova1, Oleg Posnansky2, N. J. Shah2,3
1Medical Imaging Physics, Institute of Neuroscience and Medicine - 4, Forschungzentrum Juelich, Juelich, Germany; 2Medical Imaging Physics, Institute of Neuroscience and Medicine - 4 , Forschungzentrum Juelich, Juelich, Germany; 3Department of Neurology, Faculty of Medicine, RWTH Aachen University, Aachen, Germany
Imperfections in the diffusion-weighted (DW) gradients may cause errors in the estimation of diffusion parameters. We present results demonstrating the influence of these errors in the accuracy of fibre orientation density function (ODF) estimation. A DW gradient calibration scheme, used to mitigate DW gradient errors, is also described. We compared the reconstructed fibre ODFs from two datasets, acquired in vivo with and without the application of the calibration scheme and calculated the statistical efficiency of the unbiased fibre ODF estimators for these datasets. It is shown that the calibration procedure can significantly improve results of the fibre ODF estimation.
1694. Riemannian Median and Its Applications for Orientation Distribution Function Computing
Jian Cheng1,2, Aurobrata Ghosh1, Tianzi Jiang2, Rachid Deriche1
1INRIA Sophia Antipolis, Sophia Antipolis, Valbonne, France; 2Institute of Automation, Chinese Academy of Sciences, Beijing, China
In this work, we prove the unique existence of the Riemannian median in the space of Orientation Distribution Fuction. Then we explore its two potential applications, median filtering and atlas estimation.
1695. Impact of Outliers in DTI and Q-Ball Imaging - Clinical Implications and Correction Strategies
Michael Andrew Sharman1, Julien Cohen-Adad2, Maxime Descoteaux3, Arnaud Messé4,5, Habib Benali4,5, Stéphane Lehericy6,7
1UMR-S975, CRICM-UPMC/Inserm, Paris, Île-de-France, France; 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, United States; 3Department of Computer Science, Sherbrooke University, Québec, Canada; 4UMR-S678, UPMC/Inserm, Paris, France; 5IFR49, Paris, France; 6Centre for NeuroImaging Research (CENIR), Hospital Pitié-Salpêtrière , Paris, France; 7UMR-S975, CRICM-UPMC/Inserm, Paris, France
Corrupted images within acquired diffusion weighted MRI data can have an impact on the estimation of the tensor (in diffusion tensor imaging) and diffusion ODF (in q-ball imaging). In this study we performed a series of simulations and real data analyses to quantify this impact on derived metrics such as fractional anisotropy (FA) and generalised FA. From the results of these invetigations, we propose processing strategies to detect and correct corruption artifacts arising from large, unpredicatable signal variations.
1696. In the Pursuit of Intra-Voxel Fiber Orientations: Comparison of Compressed Sensing DTI and Q-Ball MRI
Bennett Allan Landman1,2, Hanlin Wan2,3, John A. Bogovic3, Peter C. M. van Zijl, 2,4, Pierre-Louis Bazin5, Jerry L. Prince, 2,3
1Electrical Engineering, Vanderbilt University, Nashville, TN, United States; 2Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States; 3Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, United States; 4F.M. Kirby Center, Kennedy Krieger Institute, Baltimore, MD, United States; 5Radiology, Johns Hopkins University, Baltimore, MD, United States
Q-ball imaging offers the potential to resolve the DTI crossing-fiber problem by acquiring additional diffusion sensitized scans. Yet, practical constraints limit its widespread adaptation in clinical research. Recently, compressed sensing has characterized regions of crossing fibers using traditional DTI data (i.e., low b-value, 30 directions). Here, we compare q-ball and compressed sensing in simulated and in vivo crossing-fibers. Compressed sensing estimates intra-voxel structure with greater reliability than traditional q-ball while using only 13% of the scan time. Hence, compressed sensing has the potential to enable clinical study of intra-voxel structure for studies that have hitherto been limited to tensor analysis.
1697. Compressed Sensing Based Diffusion Spectrum Imaging
Namgyun Lee1, Manbir Singh2,3
1Biomedical Engieering, University of Southern California, Los angeles, CA, United States; 2Biomedical Engineering; 3Radiology, University of Southern California
Reconstruction of the PDF and ODF by Compressed Sensing based diffusion Spectrum Imaging method
1698. Accelerated Diffusion Spectrum Imaging in the Human Brain Using Compressed Sensing
Marion Irene Menzel1, Kedar Khare2, Kevin F. King3, Xiaodong Tao2, Christopher J. Hardy2, Luca Marinelli2
1GE Global Research, Munich, Germany; 2GE Global Research, Niskayuna, NY, United States; 3GE Healthcare, Waukesha, WI, United States
We developed a new method to accelerate diffusion spectrum imaging (DSI) in the human brain using compressed sensing (CS) to an extent that can be tolerated in volunteers and patients. We performed simulations and real experiments in brains of healthy volunteers, where we undersampled q-space with different sampling patterns and reconstructed it using CS. We could demonstrate that even with acceleration up to factors of R = 4 essential information on diffusion, such as orientation distribution function (ODF) and diffusion coefficients are retained. Shortening DSI acquisitions significantly by means of CS would open up the door to new contrasts, which are truly based on underlying tissue properties.
1699. Diffusion Histogram as a Marker of Fiber Crossing Within a Voxel
Bryce Wilkins1, Manbir Singh2
1Biomedical Engineering, University of Southern California, Los Angeles, CA, United States; 2Radiology and Biomedical Engineering, University of Southern California, Los Angeles, CA, United States
A simulation and experimental study of the histogram generated from the normalized diffusion signal measured along multiple gradient directions is presented. Voxels exhibiting an FA of at least 0.8 are identified as representative of single fiber voxels, and used to derive diffusion signals for multiple fiber crossings, in the range 0-90deg. The results illustrate how the histogram changes systematically with crossing fibers within a voxel, and suggests that the histogram can be used as a marker of the number of fibers within a voxel, and their relative orientation.
1700. High Resolution in Vivo DTI of the Mouse Brain: Comparison of a Cryogenic Coil with a Room Temperature Coil
Andreas Lemke1, Patrick Heiler1, Bram Stieltjes2, Andreas Neumann3, Lothar Rudi Schad1
1Deparmtent of Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany; 2Deparmtent of Radiology, German Cancer Research Center, Heidelberg, Germany; 3Department of Molecular Neurobiology, German Cancer Research Center, Heidelberg, Germany
A comparison of the SNR in DTI images acquired with a cryogenic coil and a room temperature (RT) surface coil and a comparison performed by qualitative assessment of the calculated fractional anisotropy (FA)-maps at different spatial resolutions were performed on mice brain at a 9.4 T animal scanner. The SNR of the cryogenic coil was about threefold higher compared to the SNR of the RT surface coil and the quality of the FA-maps acquired with a high in plane resolution and the cryogenic coil were significantly improved compared to the RT-coil.
1701. Characterization of White Matter Maturation in Cats: Diffusion Spectrum Imaging Tractography
Qin Chen1,2, Emi Takahashi3, Guangping Dai1, Ellen Grant, 1,3
1Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Martinos Center for Biomedical Imaging, Charlestown, MA, United States; 2Department of Neurology, West China Hospital of Sichuan Univeristy, Chengdu, Sichuan, China; 3Divison of Newborn Medicine, Department of Medicine and Department of Radiology, Children¡¯s Hospital Boston, Harvard Medical School, Boston, MA, United States
We have shown that at postnatal day (P) 35 kittens, the degrees of myelination varied in white matters in different brain areas (Takahashi et al., 2009). Our purpose of current study was to quantify the FA and ADC values on different fiber tracts in this specific developmental phase of juvenile kitten to characterize regional difference in degrees of maturation, and to compare these values between P35 (pediatric). Using high-resolution diffusion spectrum imaging (DSI) tractography, we successfully imaged the 3-dimensional structure of the cortical and subcortical pathways in P35 cats.
1702. DTI Study of Development and Aging of the Optic Nerve in Rhesus Monkeys
Yumei Yan1, Longchuan Li2, Govind Nair2, Todd Preuss3, Mar Sanchez4,5, Mark Wilson3, Xiaoping Hu2, James Herndon3, Xiaodong Zhang1
1Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States; 2biomedical engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, United States; 3Neuroscience Division, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States; 4Psychiatry & Behavioral Sciences, School of Medicine, Emory University, Atlanta, GA, United States; 5Psychobiology Division, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States
Non-human primate model was employed to access the optic nerve (ON) development and aging with Diffusion tension imaging (DTI). ADC and FA evolution in the ON of monkeys was investigated systematically. Significant changes were found between 21 months with 6 years of age, but not observed in the ON in early development. Furthermore, DTI revealed age-related changes in older rhesus monkeys that may represent axonal and myelin degeneration. DTI may provide a means to evaluate ON disorders or injury.
Andre Obenaus1,2, Stephan Ashwal3, Jerome Badaut Badaut3
1Radiation Medicine, Loma Linda University, Loma Linda, CA, United States; 2Radiology, Loma Linda University, Loma Linda , CA, United States; 3Pediatrics, Loma Linda University, Loma Linda, CA, United States
Diffusion weighted MRI is widely used in clinical diagnosis. To date the underlying molecular mechanism responsible for changes in the apparent diffusion coefficient (ADC) are poorly understood. Using small interference RNA directed against the astrocytic water channel, acqueporin-4 (AQP4), we were able to demonstrate a 50% decrease in ADC values when AQP4 expression was silenced (25%). Thus, astrocytic AQP4 contributes significantly to the ADC values in normal rodent brain. These results suggest new possibilities for interpreting ADC values in normal brain and under pathological conditions.
1704. Anatomical Phenotyping of a Mouse Model with Known White Matter Abnormalities
Jacob Ellegood1, Ameet S. Sengar2, M W. Salter2, S E. Egan3, Jason P. Lerch1, R M. Henkelman1
1Mouse Imaging Centre, Hospital for Sick Children, Toronto, Ontario, Canada; 2Neuroscience and Mental Health, Hospital for Sick Children, Toronto, Ontario, Canada; 3Developmental Biology, Hospital for Sick Children, Toronto, Ontario, Canada
Anatomical phenotyping in mouse has shown to be useful for determining small changes in volume. Similarly, Diffusion Tensor Imaging (DTI) of fixed mouse brain has been useful in assessing development and genetic differences in wild type and knockout mouse models. The purpose of this study was to determine both the volume and white matter structural changes in a mouse model with known white matter abnormalities. While some of the fractional anisotropy changes can be attributed to corresponding decreases in the volume, some structures and regions have changes that would go unnoticed if only volume or fractional anisotropy was measured.
1705. Fractional Anisotropy Changes Following Blood Brain Barrier Disruption
Ashley D. Harris1,2, Linda B. Andersen, 2,3, Henry Chen, 2,4, Pranshu Sharma2, Richard Frayne, 2,3
1School of Psychology, CUBRIC, Cardiff University, Cardiff, United Kingdom; 2Seaman Family MR Research Centre, Foothills Medical Centre, Calgary, Alberta, Canada; 3Clinical Neurosciences and Radiology, Univerisity of Calgary, Calgary, Alberta, Canada; 4Physics, Univerisity of Calgary, Calgary, Alberta, Canada
The evolution of FA is examined in a canine model following blood brain barrier disruption with hypertonic mannitol solution. White matter and grey matter show different FA responses to blood brain barrier disruption. White matter decreases, while grey matter showed significant increases. With additional understanding, FA may assist in determining the integrity of the blood brain barrier.
1706. Early Diffusion Changes Following Controlled Cortical Impact Injury on a Rat Model
Jiachen Zhuo1,2, Su Xu1,2, Jennifer Racz3, Da Shi1,2, Gary Fiskum3, Rao Gullapalli1,2
1Radiology, University of Maryland School of Medicine, Baltimore, MD, United States; 2Core for Translational Research in Imaging at Maryland (C-TRIM), University of Maryland School of Medicine, Baltimore, MD, United States; 3Anesthesiology and the Center for Shock Trauma and Anesthesiology Research, University of Maryland School of Medicine, Baltimore, MD, United States
The understanding of tissue alterations at an early stage following traumatic brain injury (TBI) is critical for injury management and prevention of more severe secondary damage. In this study, we investigated the early changes in tissue water diffusion at 2 hours and 4 hours following mild to moderate controlled cortical impact injury on a rat model. Our study indicates a distance effect from the site of injury and suggests a therapeutic window of about 2-3 hours to limit the cascade of events that may lead to secondary injury.
1707. A Longitudinal Study of DTI in a Nonhuman Primate Model of Neuro-AIDS
Chun-xia Li1, Xiaodong Zhang1, Yingxia Li1, Amelia Komery2, Francis J. Novembre3, James G. Herndon2
1Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30329, United States; 2Divisions of Microbiology and Immunology, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30322; 3Divisions of Neuroscience, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30322
DTI has been proposed as a quantitative marker of the neurological status of HIV+ patients. In this study, DTI imaging was used to longitudinally detect white matter abnormalities in whole brain and specific regions of Simian immunodeficiency virus (SIV)-infected monkeys, a reduction in FA and an increase in MD were observed evidently after viral inoculation and whole-brain FA changes correlated significantly with CD4 depletion. Findings from this investigation support the use of DTI for measurement of HIV associated neuropathologic changes. Further longitudinal study is needed to investigate the validation of DTI measures as a marker for disease progression.
1708. Hyperammonemia and Edema: A DTI Study in the Adult Rat Brain
Nicolas Kunz1,2, Cristina Cudalbu1, Yohan Van de Looij1,2, Petra Hüppi2, Stephane Sizonenko2, Rolf Gruetter1,3
1Laboratory of functional and metabolic imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 2Division of Child Growth &Development, University of Geneva, Geneva, Switzerland; 3Department of Radiology, University of Geneva & Lausanne, Geneva & Lausanne, Switzerland
Ammonia is a neurotoxin that is implicated in the pathogenesis of hepatic encephalophaty, which is reported to be responsible for brain edema. It is not yet clear whether brain edema is mostly vasogenic or cytotoxic. The aim of this study was to assess the effects of hyperammonemia on the rat brain by using DTI at 9.4T. This study shows a rapid increase of the ventricle size during the three first hours of infusion along with a decrease in ADC. As the ventricle size gets stabilized after 6h, the ADC keeps on decreasing, indicating the formation of mild cytotoxic edema.
1709. Comparison of ADC Values Using Pulsed Field Gradient and Correlation Time Diffusion Techniques in a Murine Model of Steatohepatitis at 11.7T
Stephan William Anderson1, Jorge A. Soto1, Holly N. Milch1, Hernan Jara1
1Radiology, Boston University Medical Center, Boston, MA, United States
The purpose of this study was to compare the ADC values obtained using pulsed field gradient (PFG) and correlation time diffusion (CT-D) techniques in a mouse model of steatohepatitis at 11.7T. C57BL/6 mice fed a methionine-deficient choline-deficient (MCD) diet to induce steatohepatitis were sacrificed intermittently throughout this period for ex vivo liver imaging. A comparison of the parametric maps and whole sample histograms generated by the PFG and CTD techniques shows excellent agreement between the two diffusion techniques. In all cases CT-D parametric maps had significantly higher SNR and the histogram width was narrower than those generated using PFG technique.
1710. Blood-Flow MRI of Non-Human Primate (Baboon) Retina
Hsiao-Ying Wey1, Jinqi Li1, Jiongjiong Wang2, Sung-Hong Park1, Timothy Q. Duong1
1Research Imaging Institute, UT Health Science Center at San Antonio, San Antonio, TX, United States; 2Radiology, University of Pennsylvania, Philadelphia, PA, United States
Quantitative blood flow measurement of the retina is critically important as many retinal diseases could perturb basal blood flow and blood flow responses to stimulations. In this study, we developed and applied the pseudo-continuous ASL to improve ASL contrast, and systematically explored blood-flow MRI of the retina in anesthetized baboon on a human clinical scanner. Anesthetized baboons were used to exclude movement artifacts such that we could focus on evaluating hardware feasibility and imaging parameters for high-resolution quantitative BF imaging of the retina as a first step toward evaluating potential human applications.
1711. Quantitative Measurement of Cerebral Blood Flow with High Sensitivity in Mice at 9.4T
Bing Wen Zheng1, Philip Lee1, Xavier Golay1
1Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, A*STAR (Agency for Science, Technology and Research), Biopolis, Singapore
The aim of this study was to develop a practical and robust perfusion measurement with high sensitivity and stability in the mouse brain at high magnetic field strength, via the combination of flow-sensitive alternating inversion recovery (FAIR) and single-shot k space-banded gradient- and spin-echo (kbGRASE). To estimate the influence of physiological parameters on the precision and reproducibility of CBF measurements, changes in anesthesia regime, hypercapnia and body temperature were performed.
1712. Non-Invasive MRI Measurement of CBF: Validating an Arterial Spin Labelling Sequence with 99mTc-HMPAO CBF Autoradiography in a Rat Stroke Model
Tracey Anne Baskerville1, Christopher McCabe1, Jim Patterson2, Juan Chavez3, I Mhairi Macrae1, William M. Holmes1
1Glasgow Experimental MRI Centre, University of Glasgow, Glasgow, Lanarkshire, United Kingdom; 2Institute of Neurological Sciences, Southern General Hospital, Glasgow, United Kingdom; 3Discovery Translational Medicine, Wyeth Research, Collegeville, PA, United States
Arterial spin labelling (ASL) has provided some valuable insight into cerebral perfusion in stroke research. ASL has the advantages of being non-invasive, allows repeated scanning in the same subject and can generate fully quantitative cerebral blood flow (CBF) measurements; however it requires further validation in rodent stroke models. We modified a published ASL technique (Moffat et al, 2005) and validated it against an established autoradiographic technique using the SPECT ligand, 99mTC-D, L-Hexamethylpropyleneamine (99mTc-HMPAO) in a rodent stroke model. We found that relative CBF estimates in cerebral regions of interest generated from ASL and autoradiography were closely matched throught MCA territory and ASL was able to accurately detect reductions in CBF in ischaemic tissue.
1713. Quantitative CBF MRI of Anesthetized Baboon Using Pseudo-Continuous ASL
Hsiao-Ying Wey1,2, Jinqi Li1, Lisa Jones3, M Michelle Leland3, C Akos Szabo4, Jiongjiong Wang5, Peter T. Fox1, Timothy Q. Duong1,2
1Research Imaging Institute, UT Health Science Center at San Antonio, San Antonio, TX, United States; 2Radiology, UT Health Science Center at San Antonio, San Antonio, TX, United States; 3Laboratory Animal Resources, UT Health Science Center at San Antonio, San Antonio, TX, United States; 4Neurology, UT Health Science Center at San Antonio, San Antonio, TX, United States; 5Radiology, University of Pennsylvania, Philadelphia, PA, United States
This study reports the implementation and optimization of a pseudo-continuous arterial-spin-labeling technique for non-human primate (baboon) research on a Siemens 3T TIM-Trio. High-contrast basal cerebral-blood-flow (CBF) images were obtained in 2 mins at 2x2x5 mm resolution. CBF of gray matter and white matter was analyzed for two commonly used anesthetics: isoflurane and ketamine. Moreover, CBF-based fMRI, obtained with a 7-s resolution, showed robust hypercapnia-induced CBF changes. This technology is expected to provide a non-invasive means to study physiology, function, and neurovascular coupling for non-human primate research.
1714. Pulsed Arterial Spin Labeling of Hypo- And Hyperventilated Mice
Tom Dresselaers1, Wouter Oosterlinck2, Wim Robberecht3, Paul Herijgers2, Uwe Himmelreich1
1Biomedical NMR unit - MoSAIC, K.U.Leuven, Leuven, Belgium; 2Experimental Cardiac Surgery, K.U.Leuven, Leuven, Belgium; 3Exp. Neurology, K.U.Leuven, Leuven, Belgium
Arterial spin labeling methods have been widely used to study perfusion of the brain in rats and, to some extent, in mice. To study the cerebral vascular response animals are challenged with gas mixtures to induce hypercapnia or hypoxia. However, in free-breathing animals partial respiratory compensation can not be excluded. Additionally, different respiratory levels have been noted depending on strain or transgenic model or age.We demonstrate in this study how hyper and hypocapnia can be obtained in ventilated mice by adjusting the ventilation rate and tidal volume. CBF was monitored using FAIR-ASL of the brain during this protocol.
1715. Correction for the T2 Effect of Contrast Agent on Absolute CBV Quantification Using VASO
Fu-Nien Wang1, Chien-Chung Chen1, Yi-Chun Wu1, Chou-Ming Cheng2, Tzu-Chen Yeh2
1Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, Taiwan; 2Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan, Taiwan
Absolute cerebral blood volume (aCBV) can be assessed by utilizing the signal difference of vascular space occupancy (VASO) sequence before and after injection of T1 shortening contrast agent. We propose an alternative method to reduce the T2 effect when using relative long TE. Pre and post T1 fitting were used to reconstruct IR images without the post contrast T2 shortening effect. Experiments on rat model were conducted to investigate the feasibilities.
1716. MRI Measures of Cerebral Blood Flow and Cerebrovascular Reactivity in the Developing Swine Brain
Jeff D. Winter1, Stephanie Dorner2, Joseph A. Fisher3,4, Keith St. Lawrence5,6, Andrea Kassner1,7
1Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; 2Respiratory Therapy, University Health Network, Toronto, Ontario, Canada; 3Anaesthesiology, University Health Network, Toronto, Ontario, Canada; 4Physiology, University of Toronto, Toronto, Ontario, Canada; 5Imaging Division, Lawson Health Research Institute, London, Ontario, Canada; 6Medical Biophysics, University of Western Ontario, London, Ontario, Canada; 7Medical Imaging, University of Toronto, Toronto, Ontario, Canada
The swine model is an alternative to non-human primates for neuroimaging and may be suitable for studying pediatric cerebrovascular disorders. The aim of this study was to characterize swine cerebrovascular development using BOLD cerebrovascular reactivity (CVR) and ASL cerebral blood flow (CBF). We acquired data from 13 juvenile (1-12 wk) pigs. BOLD-CVR measurements exhibited a significant logarithmic increase with body weight (Pearson r>0.81 and p<0.005 for all brain regions); whereas, baseline CBF was not related to body weight. Understanding these cerebrovascular changes will benefit future developmental studies using the swine as a translational model for cerebrovascular disease.
1717. The Saline Bolus as an MR Contrast Agent
Kenneth K. Kwong1, Y Iris Chen1, Suk-Tak Chan1,2, David A. Chesler1
1MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States; 2Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong
We obtained ΔR2* maps of a saline bolus dilution of the blood of the brain. Since the MR sensitivity to the dilution of deoxyhemoglobin was small, we also investigated the ΔR2* signal of a saline bolus diluting monocrystalline iron oxide nanoparticle (MION) preloaded into the vascular system. Our preliminary data showed that while the dilution of MION by saline generated ΔR2* maps similar to reference rCBV maps made by steady state MION imaging, the saline dilution of blood needed to take into account the presence of both the rCBV and OEF components of the BOLD signal.
1718. Early Time Points Perfusion Imaging
Kenneth K. Kwong1, Timothy G. Reese1, Koen Nelissen1, Ona Wu2, Suk-Tak Chan1, Benner Thomas1, Joseph B. Mandeville1, Mary Foley1, Wim Vanduffel1, David A. Chesler1
1MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States; 2MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital,, Charlestown, MA, United States
We investigated the feasibility of making relative cerebral blood flow (rCBF) maps from MR images acquired with short TR by measuring the initial rate of Gd-DTPA arriving within a time window smaller than the tissue mean transit time τ. We named this rCBF measurement technique utilizing the early data points of the bolus the “early time points” method (ET). ET offered rCBF results of reasonable gray-white flow contrast. Better brain coverage for ET can be obtained by applying the SIR-EPI technique. Attention was paid to the noise problem around the time of arrival (TOA) of the contrast agent.
Claire Foottit1, Greg O. Cron2, Thanh Binh Nguyen2,3, Matthew J. Hogan2,3, Ian Cameron, 12
1Carleton University, Ottawa, Ontario, Canada; 2Diagnostic Imaging, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada; 3University of Ottawa, Ottawa, Ontario, Canada
For quantitative DCE-MRI of the human brain, the Gd concentration-vs-time in the superior sagittal sinus gives the venous output function (VOF). The VOF can be used to correct errors in the arterial input function, which is crucial for accurate estimation of perfusion parameters. For measuring the VOF, MR signal phase has several advantages over MR signal magnitude: superior SNR; linearity with Gd concentration; and insensitivity to blood flow, partial volumes, and flip angle variations. This work showed that phased-derived VOFs have improved accuracy and precision compared with magnitude-derived VOFs for multislice (2D) DCE-MRI studies of the human brain (n=28).
1720. Accuracy of T1-Fitting for Pharmacokinetic Analysis of Dynamic Contrast-Enhanced MRI
Paul Wessel de Bruin1, Maarten J. Versluis1, Erlangga Yusuf2, Monique Reijnierse1, Iain Watt1, Matthias J P van Osch1
1Radiology Department, Leiden University Medical Center, Leiden, Netherlands; 2Rheumatology Department, Leiden University Medical Center, Leiden, Netherlands
The accuracy of Arterial Input Function and tissue response curve calculation in Dynamic Contrast-Enhanced MRI and Pharmacokinetic Analysis can be improved by calculating T1-maps after contrast administration and dynamic acquisition. The resulting T1-fits have lower standard deviation and a higher signal-to-noise ratio which translates linearly to improved concentration curve estimation.
1721. Partial Volume Correction of Arterial Input Functions in T1-Weighted Dynamic Contrast-Enhanced MRI
Paul Wessel de Bruin1, Monique Reijnierse1, Matthias Jozef Petrus van Osch1
1Radiology Department, Leiden University Medical Center, Leiden, Netherlands
A partial volume correction method for Dynamic Contrast-Enhanced MRI is presented that can correct for underestimation of first bolus passage in T1-weighted MRI. The method improves the robustness and precision of AIF measurement, even in very small ROIs, provided that the artery is oriented parallel to the main magnetic field.
1722. Improved T1 Mapping with Iterative Actual Flip-Angle Imaging (IAFI) Technique
Yiqun Xue1, Mark A. Rosen1, Hee Kwon Song1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States
Actual flip angle imaging (AFI) technique was recently developed to estimate the true flip angle and has been used in conjunction with the variable flip angle (VFA) technique for improved T1 measurement accuracy. One of the limitations of AFI, however, is that the method assumes that T1 is much greater than the repetition time TR. When this assumption is violated, large errors can result in both the flip angle and T1 estimation. We propose an novel iterative AFI method which yields accurate T1 values without requiring that TR << T1.
1723. Filtering and Phase-Correlation Based Registration of Dynamic Contrast Enhanced Magnetic Resonance Images
Sarayu Ramachandran1, Claudia Calcagno1, Zahi Fayad1
1Translational and Molecular Imaging Institute, Mount Sinai School of Medicine, New York, NY, United States
This study covers the anisotropic diffusion filtering and phase-correlation based registration of dynamic contrast-enhanced magnetic resonance images of human carotid arteries
1724. Feasibility of Whole-Brain Dynamic Contrast Enhanced (DCE) MRI Using 3D K-T PCA
Henrik Pedersen1, Adam Espe Hansen1, Sebastian Kozerke2, Henrik B.W. Larsson1
1Functional Imaging Unit (KFNA), Glostrup Hospital, Glostrup, Denmark; 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
Dynamic contrast-enhanced (DCE) MRI currently suffers from limited spatial coverage, preventing whole-brain quantification of cerebral blood flow. This study presents a new fast 3D imaging sequence for whole-brain DCE-MRI, which achieves a spatial coverage of 20 slices per second. The new sequence achieves faster imaging by skipping the saturation recovery (SR) pulses of conventional DCE-MRI and undersampling k-space using k-t PCA and partial Fourier imaging. The overall image quality of the proposed sequence is similar to conventional DCE-MRI, but we conclude that reliable sampling of the arterial input function requires a separate data acquisition, i.e., a dual-bolus approach.
1725. Stability of Quantitative CBF Measurements Using the T1-Based DCE Approach
Otto Mølby Henriksen1, Henrik B.W. Larsson1, Adam E. Hansen1,2, Egill Rostrup1
1Functional Imaging Unit, Dept. of Clinical Physiology and Nuclear Medicine, Glostrup Hospital, Glostrup, Denmark; 2Dept. of Radiology, Glostrup Hospital, Glostrup, Denmark
Partial volume effect (PVE) may cause erroneous determination of the arterial input function (AIF) leading to inaccurate measurements of cerebral blood flow (CBF) in bolus tracking MRI. Analyzing dynamic contrast enhanced CBF measurements in healthy subjects, we studied the effect of different PVE correction methods on 1) agreement of CBF using AIF from either the right or the left internal carotid artery 2) repeatability of repeated measurements. Scaling of the AIF to the venous output function, either by least square fit or area under the concentration curves yielded better agreement and repeatability compared to cerebral blood volume correction methods.
Matthew R. Orton1, David J. Collins1, Christina Messiou1, Elly Castellano1, Jean Tessier2, Shirley Spratt3, Martin O. Leach1
1CR-UK and EPSRC Cancer Imaging Centre, Institute of Cancer Research, Sutton, Surrey, United Kingdom; 2Early Clinical Development, AstraZeneca, Alderley Park, Macclesfield, United Kingdom; 3Clinical Discovery Team, AstraZeneca, Alderley Park, Macclesfield, United Kingdom
The blood plasma curve shape is an important component of many modelling approaches for DCE imaging, and models of these curves are used to produce functional parameter estimates. For predictions or comparisons to be made using plasma curve data obtained with different injection lengths or profiles it is necessary to include the effect of the injection profile on the plasma curve. In this abstract we present a general methodology to estimate a vascular impulse response function which is independent of the injection profile, and can therefore be used to perform such predictions and comparisons.
1727. Comparison of Baseline Signal Correction Methods for Dynamic Contrast Enhanced MRI
Yiqun Xue1, Mark A. Rosen1, Hee Kwon Song1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States
In DCE-MRI, perfusion parameters are particularly sensitive to the accuracy of the baseline (pre-contrast) signal of the AIF and tumor. However, the SNR of the pre-contrast data can be very low, particularly at high spatial resolutions since the T1 of blood and tissue are much longer than the TR. In this abstract, we compare three different baseline correction methods: magnitude averaging, Rician correction and complex averaging. It is shown that with sufficient amount of baseline data, measurement errors due to noise can be reduced most effectively by averaging of the complex data.
1728. Evaluation of Anti-Angiogenic Effects of a New Synthetic Candidate Drug KR-31831 on Xenografted Ovarian Carcinoma Using Dynamic Contrast-Enhanced MRI
Jehoon Yang1, Geun-Ho Im2, Jae-Hun Kim1, Hyejung Heo2, Sera Yoon2, Eunhee Cho2, Jaewon Lee2, Jung Hee Lee1
1Radiology, Sungkyunkwan University School of Medicine, Seoul, Korea, Republic of; 2Center for Molecualr and Cellular Imaging, Samsung Medical Center, Seoul, Korea, Republic of
Converging evidences have indicated that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provides parameters indicating permeability of tumor microvessels which has been shown to be closely related to angiogenesis. Because endothelial cells are thought to be genetically stable compared with tumor cells, tumor vasculature can be one of promising target for novel anticancer agents. Therefore we designed this study to investigate the anti-angiogenic inhibitory effect of KR-31831 that was newly developed for anti-ischemic agent by our co-worker group on xenografted human ovarian carcinoma model using DCE-MRI on a micro 7.0 Tesla MR system. Our preliminary results suggest DEC-MRI may be useful tools to evaluate the anti-angiogenic effect of KR-31831 on xenografted human ovarian carcinoma model.
1729. Quantification of Blood-Brain Barrier Permeability in the Mouse Brain in Vivo
Sang-Pil Lee1,2, Jieun Kim1, Nancy Berman3
1Hoglund Brain Imaging Center, University of Kansas Medical Center, Kansas City, KS, United States; 2Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS, United States; 3Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS, United States
Measuring blood-brain barrier (BBB) permeability in mice has been challenging because estimation of vascular contrast agent concentrations in the blood is especially difficulty due to the requirement of very high spatial resolution. We have overcome the difficulty by combining pre-contrast T1 mapping and high-resolution spin-echo T1-weighted imaging. We have successfully quantified BBB permeability in vivo from the signal changes associated with uptake of Gd-DTPA following traumatic brain injury using the Patlak plot technique. Results show that significant entry of Gd into the brain was evident in the injury site with excellent linear relationship between tissue concentration of Gd and the stretched time.
1730. Blood-Brain Barrier Permeability Measured by DCE MRI Predicts Perihematomal Edema Diffusivity
Didem Bilensoy Aksoy1, Roland Bammer2, Michael Mlynash1, Sandeep N. Gupta3, Ryan W. Snider1, Irina Eyngorn1, Chitra Venkatasubramanian1, Nancy Fischbein2, Christine A.C. Wijman1
1Department of Neurology and Neurological Sciences, Stanford Stroke Center, Stanford University, Palo Alto, CA, United States; 2Department of Radiology, Stanford University, Palo Alto, CA, United States; 3Global Research Center, General Electric, Niskayuna, NY, United States
Dynamic Contrast-Enhanced (DCE) MRI was used as a tool to assess and quantify blood-brain barrier (BBB) injury following spontaneous intracerebral hemorrhage (ICH). BBB permeability and its relationship with perihematomal tissue diffusivity, a sign of edema severity, were studied. Significantly increased BBB permeability in the region immediately surrounding the hematoma was observed. BBB leakage correlated with diffusivity in the region surrounding the hematoma.
1731. Dynamic Contrast Enhanced T1-Weighted Perfusion MRI for Measuring Cerebral Perfusion Increase After Visual Stimulation
Hilde Kjeldstad Berg1, Paal Erik Goa2, Olav Haraldseth3, Henrik B W Larsson4
1HiST, Sor-Trondelag University College, Trondheim, Norway; 2Department of Diagnostic Imaging, St Olavs Hospital, Trondheim, Norway; 3Department of Circulation and Medical Imaging, Norwegian University of Science and Technology (NTNU), Trondheim, Norway; 4Functional Imaging Unit, Glostrup Hospital, University of Copenhagen, Glostrup, Denmark
The purpose of this study was to further develop and validate a new method for quantitative cerebral perfusion measurements, using dynamic contrast enhanced T1-weighted MR imaging. Healthy volunteers were examined in rest and during visual stimulation. Visual stimulation resulted in a significant increase in cerebral blood flow (CBF) in the occipital region, and the increase was in accordance with literature values. In other areas of the brain, CBF remained unchanged. Cerebral blood volume was also measured, but the increase observed was not found to be significant.
1732. Effects of Fat Saturation on Perfusion Parameter Quantifications for the Parotid Glands in Dynamic Contrast-Enhanced MRI
Su-Chin Chiu1,2, Chun-Juan Juan2, Hsiao-Wen Chung1,2, Cheng-Chieh Cheng1,2, Hing-Chiu Chang, 1,3, Hui-Chu Chiu4,5, Cheng-Hsien Hsu2,6, Cheng-Yu Chen2, Guo-Shu Huang2
1Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan; 2Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan; 3Applied Science Laboratory, GE Healthcare, Taipei, China; 4Department of Nuclear Medicine, Tri-Service General Hospital, Taipei, Taiwan; 5EMBA in Global Chinese Management, Tamkang University, Taiwan; 6Quanta Computer Inc., Taipei
The effects of fat saturation on quantitative perfusion measurements using dynamic contrast-enhanced (DCE) MRI have not been documented for the parotid glands. In this study we included phantom and in vivo studies to compare the relationship between fat content and the difference between perfusion parameters derived from non-fat-saturated (NFS) and fat-saturated (FS) DCE-MRI. Significant differences were found for all amplitude-related parameters in parotid glands but not for muscular tissue. It is suggested that the use of FS or NFS should be explicitly specified for objective comparison of perfusion parameters with DCE-MRI on fat-containing tissues such as the parotid glands.
1733. Factors Affecting the Detection of Permeability Derangements in Perfusion Imaging of Stroke Patients
Richard Leigh1, Argye Elizabeth Hillis2, Peter B. Barker3
1Neurology, Johns Hopkins Univeristy School of Medicine, Towson, MD, United States; 2Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 3Radiology, Johns Hopkins Univeristy School of Medicine, Baltimore, MD, United States
Detection of permeability derangements in stroke patients may help guide therapy and improve outcomes. PWI, which is routinely performed in stroke imaging, can be used to assess permeability derangements through accumulation of contrast into the brain parenchyma. However it is unclear how the recorded signal can be quantified and normalized across patients. We analyzed nine stroke patients with evidence of contrast leakage on PWI to see how differences in acquisition parameters affected the recorded signal. We found that the measurements were greatly affected not only by the acquisition parameters but also the tissue type from which the signal was recorded.
1734. Quantitative Analysis of Clinical Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) to Evaluate Treatment Response in Human Breast Cancer
Yanming Yu1,2, Jun Li1, Quan Jiang3, Shanglian Bao1, Yi Zhong4, Yongquan Ye2, Jiong Zhu5, Yongming Dai6, Ewart Mark Haacke2, Jiani Hu2
1Beijing key lab of medical physics and engineering, Peking University, Beijing, China; 2Department of Radiology, Wayne State University, Detroit, MI, United States; 3Department of Neurology, Henry Ford Health Sciences Center, Detroit, MI, United States; 44. Sino-Dutch Biomedical & Information Engineering, Northeastern University, Shenyang, Liaoning, China; 5Department of Radiology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai; 6Healthcare, Magnetic Resonance Imaging, Siemens Ltd. China, Shenzhen, Guangdong, China
There are several practical limitations in quantitative analysis of clinical DCE-MRI for assessing treatment response, including: 1) difficulty in obtaining an accurate arterial input function (AIF); 2) the long scanning time to accurately estimate baseline T1(0); and 3) often highly variable or unphysical results due to noise effects; 4) long computational time. We develop a method that combines a fixed-T1, the Fuzzy C-Means and the reference region model to overcome the aforementioned limitations in quantitative analysis of clinical DCE-MRI without measuring either an AIF or T1(0), and demonstrate its feasibility to assess neoadjuvant chemotherapy for breast cancer using clinical DCE-MRI.
1735. Dual-Injection of a Low- And a Macro-Molecular-Weight-Contrast Media to Monitor the Blood-Brain Barrier Status in a Glioma Model Under Therapy
Benjamin Lemasson1,2, Raphaël Serduc3, Cecile Maisin1,4, Audrey Bouchet3, Nicolas Coquery1,4, Philippe Robert5, Christopoh Segebarth1,4, Géraldine Le Duc3, Irène Tropres1,4, Chantal Rémy1,4, Emmanuel Louis Barbier1,4
1Inersm U836, Grenoble, France; 2Oncodesign Biotechnology, Dijon, France; 3ESRF, Grenoble, France; 4Université Joseph Fourier, Grenoble Institut des Neurosciences, Grenoble, France; 5Guerbet Research, Aulnay-Sous-Bois, France
Numerous anti-tumor therapies modify the permeability (increase or decrease) of tumoral or healthy vessels. Permeability can be assessed by Dynamic Contrast-Enhanced-MRI (DCE-MRI). Low- (0.5kDa) and macro (3.5kDa) -molecular-weight-CM, DCE-MRI was performed within the same imaging session on 80 rats bearing 9L gliosarcoma before and three times after treatments onset (antiangiogenic and/or synchrotron radiotherapy), searching for possible increase or decrease in vessel wall permeability. This study suggests that the choice of CM for a DCE-MRI depends on the physiological questions to be addressed. It also suggests that the use of two CM within the same MRI session is feasible.
Peter Gall1, Matthias Guether2,3, Valerij Kiselev1
1Medical Physics, University Hospital Freiburg, Freiburg, Germany; 2Fraunhofer MEVIS, Institute for Medical Image Computing, Bremen; 3Faculty for Physics and Electrical Engineering, University Bremen, Bremen, Germany
The properties of the blood transport through the brain vasculature is of fundamental interest for the diagnosis of cerebral diseases and therefore of particular interest for the associated imaging modalities in MRI such as DSC perfusion or ASL. In this work a model for a vascular tree together with laws of laminar flow are used to describe the blood transport through early branches of the vascular tree. This description is in excellent agreement with data measured using ASL.
1737. Asymmetric FAIR - FAIR with Active Suppression of Superior Tagging (FAIR ASST)
Xiufeng Li1, Subhendra N. Sarkar2, David E. Purdy3, Robert W. Haley4, Richard W. Briggs1,4
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States; 2Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States; 3Siemens Healthcare, Malvern, PA, United States; 4Internal Medicine, UT Southwestern Medical Center, Dallas, TX, United States
The superior labeling band of FAIR can also label blood, which results in adverse venous artifacts and an inconsistency between the single subtraction blood flow quantification model and the experimental data. To overcome the difficulties faced by the traditional FAIR-based PASL technique, an asymmetric FAIR - FAIR with Active Suppression of Superior Tagging (FAIR ASST) - was proposed and evaluated. Among various possible ways for the suppression of FAIR’s superior tagging, the method using one pre-inversion and two post-inversion superior saturations was found to be effective and efficient.
1738. Practical Investigation of Pseudo-Continuous Arterial Spin Labeling (PCASL) Feasibility at Very High Field (11.75T)
Guillaume Duhamel1, Virginie Callot1, Patrick J. Cozzone1, Frank Kober1
1CRMBM / CNRS 6612, Faculté de Médecine, Université de la Méditerranée, Marseille, France
A new strategy for continuous arterial spin labeling using pulsed RF and gradient fields (pCASL) has recently been developed for human studies, showing SNR advantages. pCASL should be in principle also a method of choice for small animal studies. However, its feasibility as well as its SNR advantages over pulsed ASL techniques at very high field remains to be demonstrated. In particular, the labeling efficiency is expected to be challenged by short blood T2 values and hardware constraints. This work presents a practical investigation of pCASL implementation and feasibility at very high field (11.75T) for mouse brain perfusion studies.
1739. Fast CBF Estimation in Multi-Phase Pseudo-Continuous Arterial Spin Labeling (MP-PCASL) Using Signal Demodulation
Youngkyoo Jung1, Thomas T. Liu1
1Radiology, Univerisity of California, San Diego, La Jolla, CA, United States
The multi-phase pseudo-continuous arterial spin labeling (MP-PCASL) method offers more robust cerebral blood flow (CBF) quantification than the conventional PCASL method and higher SNR than Pulsed ASL. However, the MP-PCASL method requires a per-voxel fit to the nonlinear signal equation. This time required for this nonlinear fitting procedure (about 5 minutes) can be problematic for applications such as optimized PCASL for functional MRI studies. Here we propose a signal demodulation processing method for MP-PCASL that utilizes the dominant sinusoidal component at the multi-phase frequency. We show the proposed demodulation method can provide reliable CBF estimates while providing faster estimation time.
1740. Pushing Transfer Insensitive Labeling Technique (TILT) from Pulsed Arterial Spin Labeling to Pulsed-Continuous Arterial Spin Labeling
Cheng Ouyang1, Bradley P. Sutton1,2
1Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States; 2Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States
Transfer Insensitive Labeling Technique (TILT) has been used to measure cerebral blood flow as a pulsed arterial spin labeling (PASL) method. With the MT-insensitive feature, we propose to convert the original TILT to be further developed into a novel non-flow-driven pulsed-continuous ASL technique, named pulsed-continuous TILT (pTILT), with higher signal and fewer artifacts. Simulation show comparable labeling efficiency of pTILT compared to the current pulsed-continuous flow-driven adiabatic labeling techniques. In vivo human perfusion measurements by pTILT agree with literature
1741. Continuous Arterial Spin Labeling with Reduced Power Deposition Using Velocity Dependent Labeling Power Modulation
S. L. Talagala1, W-M Luh2, H. Merkle3
1NMRF, NINDS, National Institutes of Health, Bethesda, MD, United States; 2FMRIF, NIMH, National Institutes of Health, Bethesda, MD, United States; 3LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States
Currently, CASL perfusion studies are performed using constant amplitude labeling pulses to match the average blood velocity over the cardiac cycle. This can lead to lower inversion efficiency during the high flow velocity periods. Use of higher constant labeling RF amplitudes increase the power deposition and also can reduce the inversion efficiency for lower velocities. In this work we show that real-time change in labeling RF power according velocity may be used to reduce power deposition from the labeling pulse without loss in perfusion sensitivity. This method should be especially useful for CASL at 7T and higher fields.
1742. Reduced Specific Absorption Rate (SAR) Pseudo-Continuous Arterial Spin Labeling
Hesamoddin Jahanian1,2, Douglas C. Noll1,2, Luis Hernandez-Garcia1,2
1Functional MRI Laboratory, University of Michigan, Ann Arbor, MI, United States; 2Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States
A reduced specific absorption rate (SAR) version of Pseudo-continuous arterial spin labeling (pCASL) pulse sequence is designed and implemented. Using a simulation study a set of pCASL pulse sequence parameters is found that allows reducing the flip angle of pCASL RF pulses (i.e. reducing SAR) without losing the inversion efficiency. The proposed set of parameters employs smaller slice selective gradients which leads to less acoustic noise. This makes it more desirable especially for functional MRI studies.
F. F. Paiva1, B. U. Foerster2, F. Tovar-Moll1, J. Moll1
1D’Or Institute for Research and Education, Rio de Janeiro, RJ, Brazil; 22Philips Medical Systems, LatAm, Sao Paulo, Brazil
Multiphase ASL is an effective way to overcome the regional variation of the transit time that difficult the estimation of perfusion values. However, with conventional multiple phases ASL techniques, the ASL contrast at later phases is impaired due to repeated application of excitation pulses and longitudinal relaxation making it difficult to evaluate the tissue perfusion in regions where the transit time is longer. In the present study, we present an improvement of the acquisition scheme by exploring a modulation on the flip angle of the MR acquisition to keep the ASL contrast constant over multiple phases.
David D. Shin1, Youngkyoo Jung1, Ajit Shankaranarayanan2, Khaled Restom1, Jia Guo1, Wen-Ming Luh3, Peter Bandettini3, Eric C. Wong1, Thomas T. Liu1
1University of California, San Diego, CA, United States; 2GE Healthcare, Waukesha, WI, United States; 3National Institute of Health, Bethesda, MD, United States
The optimized pseudo-continuous arterial spin labeling (Opt-PCASL) is a variant of the PCASL method that provides higher tagging efficiency through estimation and correction of phase errors. The original implementation required extensive user-intervention, including subjective definition of vascular territories and manual input of scan parameters. A new automated optimization procedure incorporates vascular territory imaging for objective measure of vessel territory maps and a scan process that requires minimal user intervention. In three healthy subjects, the phase errors were reduced below 15° after one calibration step. The approach is expected to facilitate the use of the Opt-PCASL technique for quantitative fMRI studies.
1745. Improved ASL Imaging with 3D GRASE PROPELLER
Huan Tan1, W. Scott Hoge2, Craig A. Hamilton1, Robert A. Kraft1
1Virgina-Tech Wake Forest School of Biomedical Engineering, Winston-Salem, NC, United States; 2Radiology, Brigham and Women's Hosptial, Boston, MA, United States
3D GRASE offers an inherent SNR advantage for ASL perfusion imaging over conventional 2D EPI. However, it suffers from through-plane blurring due to T2 decay that reduces image quality and limits spatial resolution. Incorporating a PROPELLER trajectory into 3D GRASE reduces the ETL and subsequently the through-plane blurring. Furthermore, a PROPELLER trajectory is less susceptible to field inhomogeneities due to its shorter echo train length. In summary, 3D GRASE PROPELLER improves ASL perfusion images without increasing scan time while maintaining the perfusion SNR.
1746. Improving the Spatial Resolution of 3D GRASE ASL
Emma Louise Hall1, Penny A. Gowland1, Susan T. Francis1
1Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom
3D-GRASE has been used with ASL but generally at coarse in-plane resolution to reduce off-resonance phase errors, and limited slice resolution to reduce through slice decay and blurring. Here we assess the use of parallel imaging combined with multi-shot acquisition and outer volume suppression (OVS) to reduce the inter-RF spacing in 3D-GRASE, allowing the acquisition of 3D-GRASE ASL data with improved spatial resolution at 3T. OVS 3D-GRASE is applied to a functional paradigm to study visual activity.
1747. Optimising Image Readout for Perfusion Imaging at 7T
Emma Louise Hall1, Penny A. Gowland1, Susan T. Francis1
1Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom
Echo Planar Imaging (EPI) is commonly used in conjunction with arterial spin labelling (ASL) due to short image acquisition times. However EP images are affected by susceptibility artifacts and chemical shift artifacts, particularly at increased field strength. Here the use of True-FISP and FLASH acquisitions are compared to EPI based ASL measurements at 7T, signal-to-noise ratio and coefficient of variation are assessed for each acquisition method. Non-EP methods are shown to be advantageous at high in-plane resolution (1 mm), with True-FISP providing the best SNR, however slice coverage is limited due to SAR at 7T.
1748. Benefits of Interleaved Continuous Labeling and Background Suppression
Weiying Dai1, Philip M. Robson1, Ajit Shankaranarayanan2, David C. Alsop1
1Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States; 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States
CContinuous arterial spin labeling (CASL) can produce greater signal and reduced dependence on arterial transit timing than pulsed ASL. These benefits of CASL are reduced, however, when the labeling duration is shortened for compatibility with background suppression. In theory, continuous labeling can be performed interleaved within the background suppression sequence as long as the labeling/control are modulated correctly. Here we compare the performance of interleaved labeling with a more traditional background suppression approach and demonstrate the increased signal achievable with the longer labeling made possible by interleaving with the background suppression.
Qiang Shen1, Gang Zhu2, Timothy Q. Duong1
1Research Imaging Institute, Ophthalmology/Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States; 2Bruker BioSpin Corporation, Billerica, MA, United States
Reduction or elimination of the static tissue signal in an arterial spin labeling (ASL) study could improve sensitivity and reproducibility. Such static tissue signal reduction has been achieved with the use of additional inversion pulses after the labeling of arterial spins in single-coil ASL techniques. This work further developed quantitative multislice CBF acquisition for the inversion recovery continuous ASL technique with a separate labeling coil that we proposed previously in rats. We further applied this approach to image focal ischemia in rats. The current IR-cASL scheme offers some unique advantages for rodent studies where the arterial transit time is short.
1750. Towards an Optimal Distribution of B-Values for IVIM Imaging
Andreas Lemke1, Frederik Bernd Laun2, Lothar Rudi Schad1, Bram Stieltjes3
1Deparmtent of Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany; 2Department of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany; 3Deparmtent of Radiology, German Cancer Research Center, Heidelberg, Germany
The b-value distribution for IVIM imaging was optimized using Monte Carlo simulations in order to minimize the uncertainty of the biexponential fit. For three different parameter settings, illustrating the IVIM parameters in brain, liver and kidney, the error of the calculated optimal b-value distribution was compared with the error of previously reported distributions. The error for this optimized distribution was significantly lower for all parameter settings when compared with currently used distributions. The results demonstrate that the presented choice of b-values can substantially minimize the overall measurement error in IVIM and may aid the choice of b-values in clinical experiments.
Christine Preibisch1, Annette Förschler1, Afra Wohlschläger1, Christian Sorg2, Alexander Kurz2, Claus Zimmer1, Panagiotis Alexopoulos2
1Abteilung für Neuroradiologie, Klinikum rechts der Isar der Technischen Universität München, Munich, Germany; 2Klinik und Poliklinik für Psychiatrie und Psychotherapie, Klinikum rechts der Isar der Technischen Universität München, Munich, Germany
Problem: The aim of the current study was to investigate the reproducibility of PASL imaging based on the PULSAR technique combined with thin slice periodic saturation (Q2TIPS) to control for bolus length and facilitate CBF quantification. Methods: Resting CBF maps were obtained from 16 subjects (30±10a) on two different days on a 3T whole body scanner. Results: Mean CBF, within-subject standard deviation and repeatability were 34.1±5.3, 3.5 and 9.7 in GM and 7.4±2.7, 2.7and 7.5 in WM (all values in ml/100g/min). Conclusion: PULSAR based perfusion measurement shows good reproducibility lying in the range detected for other ASL methods.
1752. Comparison of Inter-Session and Intra-Session Cerebral Perfusion and Arrival Time Reproducibility on a Single Subject Using Arterial Spin Labelling.
John Robert Cain1, Gerard Thompson1, Alan Jackson1, Laura M. Parkes1,2
1Imaging Science, University of Manchester, Manchester, United Kingdom; 2Biomedical Imaging Institute, University of Manchester, Manchester, United Kingdom
Groups have published reproducibility studies for arterial spin labeling (ASL) cerebral blood flow (CBF) measurements. The relatively large inter-subject variation in CBF hinders direct comparison between individuals. A single healthy volunteer underwent MRI imaging on 7 separate occasions consisting of two STAR ASL acquisitions. Intra-session reproducibility was assessed using Bland-Altman analysis of grey matter perfusion and arrival time. Inter-session and intra-session perfusion values coefficient of variation (COV) were comparable, suggesting errors due to re-positioning and physiological changes are not significant. The COV of perfusion values are consistent with published results using multiple individuals and the arrival time COV is superior.
1753. Inter- And Intra-Subject Variability of CBF Measurements Using PCASL Method
Tie-Qiang Li1, Tomas Jonsson1, Maria Kristoffersen Wiberg2, Jiongjiong Wang3
1Department of Medical Physics, Karolinska University Hospital, S-141 86, Stockholm, Sweden; 2Department of Radiology, Karolinska University Hospital, S-141 86, Stockholm, Sweden; 3Department of Radiology, University of Pennsylvania, United States
PCASL techniques have become very attractive for pharmacokinetics studies and clinical applications where repetitive, longitudinal, and quantitative CBF measurements are desirable. One important issue need to addressed is the inter- and intra-subject variability of the measured CBF results. In this study, we experimentally investigated this issue using an optimized PCASL protocol at 3T. The results indicate that the inter-subject variability is about 2-3 time of that for intra-subject depending the chosen ROI size (from voxel to whole brain).
1754. Maximizing Statistical Power of ASL MRI in Detecting Regional CBF Differences
Sina Aslan1, Hanzhang Lu1
1AIRC, UT Southwestern Medical Center, Dallas, TX, United States
We conducted numerical simulations and experimental measurements to see how sensitive is ASL MRI in detecting regional activity difference between patients and controls and what is the best strategy to detect such a difference. We used a model condition in which we simulated a “patient” group by having the subject view a flashing checkerboard and compared their CBF to that of a control group of subjects viewing a fixation. Our results suggest that, when it comes to detect regional CBF differences between two subject groups, rCBF is a more sensitive marker.
1755. White Matter Cerebral Blood Flow Detection Using Arterial Spin Labelling
Nyssa Elaine Craig1, Dinesh Selvarajah2, Esben Thade Petersen3, Xavier Golay4, Solomon Tesfaye5, Paul Griffiths1, Iain David Wilkinson1
1Academic Unit of Radiology, University of Sheffield, Sheffield, South Yorkshire, United Kingdom; 2Diabetes Unit, University of Sheffield, Sheffield, South Yorkshire; 3Center for Functionally Integrative Neuroscience, Aarhus University Hospital, Denmark; 4Centre for Neuroimaging Techniques, University College London, London, United Kingdom; 5Diabetes Unit, University of Sheffield, Sheffield, South Yorkshire, United Kingdom
The sensitivity of the Arterial Spin Labelling technique to detect Cerebral Blood Flow (CBF) within the white matter of the brain has been under dispute for some time. The present study poses a vasodilatory challenge to thirteen normal, healthy control subjects using Acetazolamide, and uses the QUASAR sequence to assess CBF both pre- and post-administration. The results show a high contrast to noise ratio, with a statistically significant increase in mean white matter perfusion across all subjects, indicating that the effect can be detected in this tissue type, despite lower absolute flow values than those detected in grey matter.
1756. Hippocampus Perfusion Studies Using OPTIMAL FAIR
Xiufeng Li1, Subhendra N. Sarkar2, David E. Purdy3, Robert W. Haley4, Richard W. Briggs1,4
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States; 2Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States; 3Siemens Healthcare, Malvern, PA, United States; 4Internal Medicine, UT Southwestern Medical Center, Dallas, TX, United States
To facilitate reliable and sensitive perfusion measurements in the sub-regions of the hippocampus, we developed OPTIMAL FAIR (orthogonally positioned imaging tagging method for arterial labeling with FAIR) and performed comprehensive optimization studies for the proper selection of arterial spin labeling parameters. Study results indicated that the anterior segment of the hippocampus has different blood flow dynamic characteristics from the other parts of the hippocampus, e.g. the lowest perfusion and the longest transit time, which can be due to different sources of arterial blood supply.
1757. Regional Cerebral Blood Flow Changes of a SIV-Infected Monkey Model of Neuro-AIDS
Chun-xia Li1, Xiaodong Zhang1, Amelia Komery2, Francis J. Novembre2, James G. Herndon3
1Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30329, United States; 2Divisions of Microbiology and Immunology, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30322; 3Divisions of Neuroscience, Yerkes National Primate Research Center, Emory University, Atlanta, GA,30322
The regional cerebral blood flow (rCBF) measure has been proposed as a biomarker for HIV-associated CNS damage. In this study we used the continuous arterial spin labeled (CASL) MRI technique to quantitatively measure the longitudinal pattern of rCBF change in the selected ROIs of Simian Immunovirus Virus (SIV)-infected monkey model following infection. The finding indicates rCBF in selected ROIs declined after the SIV inoculation resembling with the HIV+ patient, and the rCBF changes correlated well with the depletion of CD4, which suggests CASL may be a surrogate biomarker for accessing the progression of the disease and treatment development.
1758. Simultaneous CBF and BOLD Mapping of Electrical Acupoint Stimulation Induced Brain Activity
Yue Zhang1, Christopher B. Glielmi, Yin Jiang2, Jing Liu3, Ying Hao4, Xiaoying Wang3,4, Jing Fang, 1,4, Jisheng Han2, Jue Zhang, 1,4, Xiaoping Hu5
1College of Engineering, Peking University, Beijing, China; 2Neuroscience Research Institute, Peking University, Beijing, China; 3Dept.of Radiology, Peking University First Hospital, Beijing, China; 4Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China; 5Dept. of Biomedical Engineering, Georgia Institute of Technology / Emory University, Atlanta, United States
Blood oxygenation level dependent (BOLD) technique has been used to map brain activity related to electrical acupoint stimulation (EAS) in previous pain-relief studies, but introduces relatively poor reproducibility and consistencies. In this study, the dual-echo based simultaneous acquisition of cerebral blood flow (CBF) and BOLD was employed to provide the first evidence of CBF response to EAS and inter-subjects¡¯ variation was compared between the two techniques. The results suggested that the sensitivity and specificity to sensory and pain-related regions were consistent with previous findings. Moreover, CBF based inter-subjects¡¯variation had a significant decrease than BOLD.
Jeff D. Winter1, Jackie Leung1, Manohar Shroff2,3, Andrea Kassner1,3
1Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada; 2Diagnostic Imaging, The Hospital for Sick Children, Toronto, Ontario, Canada; 3Medical Imaging, University of Toronto, Toronto, Ontario, Canada
Cerebrovascular reactivity (CVR) measures of the cerebral blood flow (CBF) response to CO2 may benefit clinical assessment of cerebrovascular disease. CVR imaging is typically performed using indirect BOLD signal changes or arterial spin labeling (ASL) CBF measures. In this study, we compared between-day reproducibility of BOLD and ASL (Look-Locker acquisition) CVR measures performed with controlled CO2 transitions in adults. Reproducibility was quantified with the between-day coefficient of variation (CV). Reproducibility of ASL-CVR measures of CBF the response to CO2 (CV < 17%) were similar to BOLD-CVR (CV < 19%), which points to the potential clinical utility of this method.
1760. A Distributed Network of Cerebral Blood Flow Changes Accurately Discriminates Methylphenidate and Atomoxetine: A Gaussian Process Pattern Recognition Approach
Andre Marquand1, Sara De Simoni, Owen O'Daly, Fernando Zelaya, Mitul Mehta
1Centre for Neuroimaging Sciences, Institute of Psychiatry, London, United Kingdom
Methylphenidate and atomoxetine are widely used for the treatment of attention-deficit/hyperactivity disorder, but their differential effects on human brain physiology are poorly understood. We apply a multivariate pattern recognition algorithm (Gaussian process classification) to continuous arterial spin labelling data recorded while subjects were at rest which accurately discriminates methylphenidate from atomoxetine and each drug from placebo. We show a distributed network of brain regions underlies discrimination, with differential effects in putamen, anterior cingulate and temporal poles. Multivariate pattern recognition may be a useful technique for detection of diffuse pharmacological effects.
1761. Does Pulsed Arterial Spin-Labeling Selectively Underestimate Responses to Global Challenges?
Felipe B. Tancredi1,2, Claudine J. Gauthier, 2,3, Cécile J. Madjar2, Richard D. Hoge1,2
1Biomedical Engineering, Université de Montréal, Montreal, Quebec, Canada; 2UNF, CRIUGM, Montreal, Quebec, Canada; 3Physiology, Université de Montréal, Montreal, Quebec, Canada
ASL is a technique of particular interest for studies in which hypercapnia challenge is employed. We sought to test whether the shortening in blood transit time that vasodilation by moderate hypercapnia may cause was leading to a systematic underestimation of perfusion responses measured with ASL. We measured flow responses in three different moments: at hypercapnia, during visual stimulus and when both were simultaneously present. We found that the response to the combined stimulus was a linear combination of the responses the individual stimulus alone, that’s to say, the focal response to a visual stimulus during hypercapnia challenge was not underestimated. ASL is a technique of particular interest for studies in which hypercapnia challenge is employed. We sought to test whether the shortening in blood transit time that vasodilation by moderate hypercapnia may cause was leading to a systematic underestimation of perfusion responses measured with ASL. We measured flow responses in three different moments: at hypercapnia, during visual stimulus and when both were simultaneously present. We found that the response to the combined stimulus was a linear combination of the responses the individual stimulus alone, that’s to say, the focal response to a visual stimulus during hypercapnia challenge was not underestimated.
1762. Dynamic Changes in Blood Transit Time and Flow During Somatosensory Stimulation Measured by Dynamic ASL with High Temporal Resolution
Yuguang Meng1, Seong-Gi Kim1,2
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States; 2Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, United States
The blood transit time from arterial spin labeling plane to capillaries in the imaging slice (referred to as “tissue transit time”) decreased during neuronal activation in humans, while it appeared no changes during somatosensory stimulation in rats. Since a tissue transit time is shorter in rats compared to humans, shortening blood transit time may not be detectable with arterial spin labeling (ASL) data with low temporal resolution. Thus, it is important to carefully measure dynamic transit time changes during stimulation. In this work, the dynamics of both CBF and the blood transit time during rat forepaw stimulation were simultaneously measured with a modified dynamic ASL (DASL) method with improved temporal resolution.
1763. ASL Based PhMRI in Assessing Serotonergic Response in Users of XTC
Marieke L. Schouw1, Sanna Gevers1, Charles B.L.M. Majoie2, Jan Booij3, Aart J. Nederveen, Liesbeth Reneman
1Radiology, AMC, Amsterdam, Noord-Holland, Netherlands; 2Radiology, AMC, Amsterdam, Netherlands; 3Nuclear Medecine, AMC, Amsterdam
We investigate whether pharmacologic magnetic resonance imaging (phMRI) is suitable in detecting serotonin terminal loss in users of XTC (MDMA, ecstasy). 10 XTC users and 7 controls underwent ASL (arterial spin labelling) based phMR imaging with a challenge with the selective serotonin reuptake inhibitor (SSRI) citalopram. Data were combined with single photon emission computed tomography (SPECT) imaging with [123I]â-CIT. Markedly different citalopram-induced CBF changes were observed in XTC users compared to controls, in brain regions that also showed (a tendency) towards reduced SERT densities. These preliminary results suggest that ASL-based CBF measurements may be indirect measures of serotonin terminal loss.
1764. Intra and Extracranial Carotid Artery Perfusion Imaging Based on MR Vessel Encoded Arterial Spin Labeling
Ying Sun1, Bing Wu2, Hua Zhong3, Xiaoying Wang2, Jue Zhang1,3, Jing Fang1,3
1College of Engineering, Peking University, Beijing, China; 2Dept. of Radiology, Peking University First Hospital, Beijing, China; 3Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
With the increase of cases of intracranial stenosis, the research to study the shortcut pathways caused by carotid artery stenosis manifested by abnormal external carotid artery perfusion image become very critical. In this preliminary study, an upgraded tagging strategy for Vessel Encoded Arterial Spin Labeling (VEASL) was employed to non-invasively evaluate the intra and extracranial carotid artery supplied cerebral perfusion of healthy volunteers, by tagging the right and left internal carotid arteries, the external carotid artery and the vertebral arteries. Results suggested that the proposed approach could separate the intracranial and extracranial parts of perfusion come from external carotid artery.
1765. Accelerated Territorial ASL Based on Shared Rotating Control Acquisition: Validation Observer Study
Hironori Kamano1, Takashi Yoshiura1, Ivan Zimine2, Akio Hiwatashi1, Koji Yamashita1, Yukihisa Takayama1, Eiki Nagao1, Hiroshi Honda1
1Department of Clinical Radiology, Kyushu University, Fukuoka, Japan; 2Philips Electronics Japan
Use of shared rotating control acquisition has been reported to substantially shorten total acquisition time in territorial ASL, while it may result in inaccurate estimate of ƒ´M from each feeding vessels due to incomplete compensation of magnetization transfer effects. In order to validate this technique in actual clinical interpretation, we performed an observer test. Results indicated an excellent over all agreement between the shared rotating control and normal control acquisitions. There was a tendency that, in the shared rotating control method, the territorial information may be less reliable in the territories of the posterior cerebral artery.
1766. Combined Assessment of Vascular Territories and Haemodynamic Parameter Maps
Rebecca Susan Dewey1,2, Dorothee P. Auer1, Susan T. Francis2
1Division of Academic Radiology, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom; 2Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom
Watershed areas are brain regions supplied by the most distal branches of the cerebral arteries and are most susceptible to haemodynamic ischaemia. We assess the use of territorial ASL to define Left and Right Internal Carotid, Anterior Cerebral, and Basilar Artery territories to distinguish the watershed area, and assess its correspondence with haemodynamic parameters (perfusion rate, arterial blood volume and arterial and tissue transit times) from multiphase ASL. Specified anatomical regions are assessed for vascular supply and haemodynamic parameters. Combining these techniques, an atlas of parameters can be formed for region-specific perfusion and position and functional effects of watershed areas.
1767. Simultaneous Measurements of Arterial Transit Times and Water Exchange Rates by Diffusion-Weighted ASL
Keith S. St. Lawrence1,2, Jodi Miller1, Jiongjiong Wang3
1Imaging, Lawson Health Research Institute, London, ON, Canada; 2Medical Biophysics, University of Western Ontario, London, ON, Canada; 3Radiology, University of Pennsylvania, Philadelphia, PA, United States
The arterial transit time (τa) and the exchange rate of water (kw) across the blood-brain barrier were determined using diffusion-weighted arterial spin labelling (ASL) with multiple post-labelling delay times. τa was determined using bipolar gradients to suppress the arterial signal (i.e., the FEAST method) and kw was determined using bipolar gradients strong enough to suppress all vascular signals and a kinetic model to characterize water exchange across the BBB. Averaged over four volunteers, kw was 119 min-1 in grey matter and τa was 1.26 s. From repeat measurements, the intra-subject coefficient of variation of kw was 12%.
1768. Flow-Weighted Arterial Transit Time Mapping of the Human Brain
Toralf Mildner1, Stefan Hetzer1, Wolfgang Driesel1, Karsten Müller1, Harald E. Möller1
1NMR unit, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany
Mapping of Arterial Transit times by Intravascular Signal SElection (MATISSE) was performed with and without a mild flow-weighting (FW). The arterial transit times, δa, of the flow-weighted data were increased on average by about 700 ms and the signal amplitudes roughly were halved. Flow-through signals, i. e. signals of arterial vessels permeating the voxel, are removed almost completely, although the MATISSE signal still is expected to be of vascular origin. The fact that δa with mild FW was found to be easily larger than 2 s might be important for the quantification of CBF in standard dual-coil CASL experiments.
1769. Arterial Transit Delay Measurement Using Pseudo-Continuous ASL with Variable TR and Interleaved Post-Labeling Delays
Kun Lu1, Thomas T. Liu1, Youngkyoo Jung1
1Center for Functional MRI, UCSD, La Jolla, CA, United States
Conventional arterial transit delay measurements consist of a series of separate ASL experiments acquired at several different post-labeling delays. Such measurements are usually time-consuming and can be formidable overheads for ASL studies. The time requirement also makes the measurements highly sensitive to motion. This study presents a simple yet effective modification of the conventional method for measuring transit delay with shorter scan time and less motion sensitivity. Such a method could be beneficial to all ASL studies.
1770. Eliminating the Partition Coefficient from ASL Perfusion Quantification with a Homogeneous Contrast Reference Image
Weiying Dai1, Philip M. Robson1, Ajit Shankaranarayanan2, David C. Alsop1
1Radiology, Beth Israel Deaconess Medical Center,Harvard Medical School, Boston, MA, United States; 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States
Conventional ASL perfusion quantification requires division by a proton density reference image and assumes a uniform brain-blood partition coefficient. The brain-blood partition coefficient is not constant, however, and may especially differ in areas of pathology. In cortical regions where CSF, white matter and gray matter may all be mixed within a voxel, division by the proton density image can also add nonlinear systematic errors. Here we propose using an optimized inversion preparation to generate an image whose intensity is essentially independent of tissue type. This highly homogeneous image can replace the proton density image and makes the assumption of a brain-blood partition coefficient unnecessary. In-vivo results demonstrate that such homogeneous contrast is achievable and can be used to improve the pixel-by-pixel perfusion measurement.
1771. Potential Tracking of Oxygen Consumption Using Arterial Spin Labeling Susceptibility Imaging
Johannes Gregori1,2, Norbert Schuff3,4, Matthias Günther1,5
1Institute for Medical Image Computing, Fraunhofer MEVIS, Bremen, Germany; 2Neurology, Universitätsmedizin Mannheim, Heidelberg University, Mannheim, Germany; 3Radiology & Biomedical Imaging, University of San Francisco, San Francisco, CA, United States; 4Center for Imaging of Neurodegenerate Diseases (CIND), VA Medical Center, San Francisco, CA, United States; 5mediri GmbH, Heidelberg, Germany
We present ASL time series measurements with spin/gradient double echo spiral 3D-GRASE readout to quantify R2' of the ASL difference signal. R2' can give information about blood oxygenation and blood volume, while ASL time series are used to investigate perfusion dynamics. Using the combination of both techniques, we can measure the changes of R2' over different inflow times and discuss the physiological underlyings.
1772. Improving the Stability of T2 Measurements in ASL Experiments
Johanna Kramme1,2, Johannes Gregori1,2, Matthias Günther2,3
1Division of Neurology, University Hospital Mannheim of the University of Heidelberg, Mannheim, Germany; 2Fraunhofer MEVIS-Institute for Medical Image Computing, Bremen, Germany; 3Faculty for Physics and Electrical Engineering, University Bremen, Bremen, Germany
To increase sensitivity and reduce physiological noise in ASL T2 measurements a single shot 3D-GRASE approach was developed. Compared to sequential acquisition of the different echo times significant reduction in scan time and physiological noise can be achieved. To improve T2 calculations the inflow time TI of each data set has to be corrected for each echo time. Based on the TE correction of TI the reliability of the T2 estimate could be improved by a factor of two and more. With these improvements ASL T2 measurements become feasible in a clinical stetting.
1773. Dynamic MR Angiography and Microvascular Flow Imaging with High Temporal Resolution Using TrueFISP Based Spin Tagging with Alternating Radiofrequency (TrueSTAR)
Lirong Yan1, Yan Zhuo1, Jing An2, Jiongjiong Wang3
1Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; 2Siemens Mindit Magnetic Resonance, Siemens Healthcare, MR Collaboration NE Asia, Shenzhen, China; 3Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
In the present study, we present a novel technique termed TrueFISP based Spin Tagging with Alternating Radiofrequency (TrueSTAR) for both time-resolved 4-D MR angiography (MRA) and dynamic microvascular flow (perfusion) imaging. We demonstrate that TrueSTAR is able to delineate the dynamic filling of cerebrovasculature with a spatial resolution of 1x1x1mm3 and a temporal resolution of 50ms. Dynamic microvascular flow imaging using TrueSTAR is able to follow hemodynamic changes during visual cortex activation every 85ms.
1774. Flow Measurement Using Arterial Spin Labeling with Flow Discrimination by Cumulative Readout Pulses
Yi Wang1,2, Allison Payne3, Seong-Eun Kim3, Edward DiBella3, Dennis L. Parker3
1Bioengineering, University of Utah, Salt Lake City, UT, United States; 2Utah Center for Advanced Imaging Research , University of Utah, Salt Lake City, UT, United States; 3Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States
The Pennes bioheat transfer equation (BHTE) is the most widely used equation to model the effects of heat deposition and dissipation in tissues. The formulation includes terms for thermal conductivity and an effective perfusion, which represents the rate at which blood flow removes heat from a local tissue region. MR thermometry has allowed accurate estimations of these subject-specific thermal properties. Using these estimated parameters enables more accurate treatment planning. However, tissue properties, particularly perfusion, are known to change over the course of a thermal therapy treatment. Detecting perfusion changes during a thermal therapy treatment would allow for the adjustment of treatment parameters to achieve a more efficacious therapy. In this work, we present a method to use arterial spin labeling to determine the rate at which flow passes through a point. The pulse sequence combines the turbo-FLASH imaging and Look-Locker-like readout at multiple inversion times in a single scan. The data obtained from this newly developed sequence approximates the average velocity of blood (fluid) passing through a thin slice, providing a surrogate for the Pennes’ perfusion term. This method is independent of MR thermometry, decoupling the blood flow measurement from the MR temperature maps, allowing the perfusion changes to be monitored throughout the thermal therapy session.
1775. Dynamic 3D Spin-Labeling MRA for Evaluation of Vascular Territory Inflow
Ek Tsoon Tan1, Norbert G. Campeau1, John Huston III1, Stephen J. Riederer1
1Radiology, Mayo Clinic, Rochester, MN, United States
The 3D spin-labeling MRA technique, fast inversion recovery (FIR-MRA) provides excellent vessel conspicuity and venous suppression. To incorporate temporal information with high spatial resolution for intracranial imaging at 3T, we developed a variation of the 3D FIR-MRA sequence with segmented acquisitions of four time frames during the gradient echo readout. Scan time is five minutes. Initial feasibility studies show progressive filling of vascular distributions in the subtracted angiograms, along with varying tissue contrasts in the unsubtracted images. This capability may be useful in the setting of infarction, vascular stenoses, arteriovenous malformations and aneurysms.
1776. Measurement of Arterial Blood Velocity Distribution in the Human Brain Using Velocity Selective ASL
David Dawei Ding1, Jia Guo2, Eric C. Wong3,4
1School of Medicine, University of California - San Diego, La Jolla, CA, United States; 2Department of Bioengineering, University of California - San Diego, La Jolla, CA, United States; 3Department of Radiology, University of California - San Diego, La Jolla, CA; 4Department of Psychiatry, University of California - San Diego, La Jolla , CA, United States
This study measures the distribution of brain arterial blood velocity. Five subjects were scanned using velocity selective ASL. The velocity cut off of the image acquisition was held constant at 2cm/sec while the velocity cut off of the tag was 2, 4, 8, 16, 32, and 64cm/sec. The arterial blood fraction in each velocity bin was calculated, and showed that 60% of the blood flow is below 32cm/sec, with about 10% above 64 cm/sec. This data may help to optimize the design of velocity selective inversion pulses, and may be useful in the study of cerebral vascular physiology.
1777. Comparing Kidney Perfusion Using Arterial Spin Labeling and Microsphere Methods in an Interventional Swine Model
Nathan S. Artz1, Andrew L. Wentland1, Elizabeth A. Sadowski2, Thomas M. Grist, 12, Arjang Djamali3, Sean B. Fain1,2
1Medical Physics, University of Wisconsin-Madison, Madison, WI, United States; 2Radiology, University of Wisconsin-Madison, Madison, WI, United States; 3Nephrology, University of Wisconsin-Madison, Madison, WI, United States
Two methods of measuring cortical kidney perfusion, fluorescent microspheres and ASL-FAIR, are compared for 11 swine each at four interventional time points: 1) under baseline conditions, 2) during an acetylcholine and fluid bolus challenge to increase perfusion, 3) initially after switching to isoflurane anesthesia , and 4) after two hours of isoflurane anesthesia. Across all swine, microspheres and ASL correlated (r = 0.72) and each technique tracked the expected perfusion changes due to the interventions, demonstrating statistical differences in perfusion (p < 0.05) between time points. In addition, ASL perfusion data was more consistent across swine. This data provides validation of ASL-FAIR for relative renal perfusion imaging, especially for evaluating time-averaged perfusion changes that may be observed in chronic disease.
1778. Arterial Spin Labelling Characterisation of Renal Medullary Perfusion
Philip M. Robson1, David C. Alsop1
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States
Arterial spin labelling (ASL) has recently been used for measuring renal perfusion. Perfusion is highest in the renal cortex, but the outer medulla is the most prone to hypoxic injury. Accurate quantification of outer medullary perfusion can be complicated by partial volume averaging with cortical signal and by loss of label in the cortex before transit to the medulla. Here we evaluate high resolution ASL MRI with different labelling strategies to assess the feasibility of quantifying outer medullary perfusion with ASL.
Reshmi Rajendran1, Cai-Xian Yong1, Jolena Tan1, Jiongjiong Wang2, Kai-Hsiang Chaung1
1Lab of Molecular Imaging, Singapore Bioimaging Consortium, Singapore, Singapore; 2University of Pennsylvania, United States
Synopsis We demonstrated quantitative renal perfusion in mice using ASL MRI. Perfusion was measured using a FAIR spin-echo EPI. Respiratory motion, susceptibility and fat artifacts were controlled by triggering, high-order shimming, and water excitation, respectively. High perfusion signal was obtained in the cortex compared to the medulla and signal was absent in scans carried out post mortem. Change in the cortical perfusion was observed after manipulating gas compositions including 5% CO2.
1780. Image Registration in ASL-Perfusion Imaging of Kidney - Impact on Image Quality
Kiril Schewzow1, Frank Gerrit Zöllner1, Niels Oesingmann2, Lothar Rudi Schad1
1Department of Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany; 2Siemens Healthcare, New York, United States
ASL techniques suffer from low SNR and especially in abdominal imaging, from organ movements, e.g. breathing. In this work, we analyzed the impact of automatic image registration on signal quality and increase of SNR by averaging in ASL kidney perfusion imaging. To evaluate the registration we compared results to manual registration based on landmarks. Both registration techniques improve the image quality significantly. However, the automatic is the preferred method for large data sets. In addition, a higher SNR is reached contributing to reliable quantification.
1781. Isotropic Resolution 3D Fast Spin Echo Acquisition for Quantitative Arterial Spin Labelled Perfusion Imaging in the Kidneys
Philip M. Robson1, Ananth J. Madhuranthakam2, David C. Alsop1
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States; 2Applied Science Laboratory, GE Healthcare, Boston, MA, United States
Most studies using arterial spin labelling (ASL) for perfusion in the abdomen have used 2D acquisitions in a limited number of slices. We evaluated 3D Fast Spin Echo (3D FSE) imaging for volumetric acquisition of perfusion in the kidneys. In sagittal image volumes over each kidney, isotropic 2.6-mm resolution was achieved allowing assessment in any orientation. Quantitative perfusion values were found to be comparable to a 2D ASL single-shot FSE sequence, and gave values for total renal blood flow that are in broad agreement with physiological values.
Guang Li1, Bryan De La Garza2, Eric Raymond Muir, 2,3, Timothy Q. Duong4
1Research Imaging Institute, Ophthalmology/Radiology, UT Health Science Center at San Antonio, San Antonio, TX, United States; 2Research Imaging Institute, UT Health Science Center at San Antonio, San Antonio, TX, United States; 3Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States; 42Research Imaging Institute, Ophthalmology/Radiology, UT Health Science Center at San Antonio, San Antonio, TX, United States
Vision loss due to retinal degeneration is a major problem in ophthalmology. We have previously reported a thinning of the retina and perturbed BOLD fMRI responses to physiologic challenges in the retina of an animal model of progressive retinal degeneration, Royal-College-of-Surgeons (RCS) rats. In this study, we extend previous findings by developing layer-specific basal blood flow (BF) MRI to investigate BF changes in RCS rat retinas and age-matched controls at 43 x 43 x 600 um3 on 11.7T. Quantitative BF was measured using the continuous arterial-spin-labeling technique. MRI provides layer-specific quantitative BF data without depth limitation and a large field-of-view.
Nicolas Pannetier1,2, Thomas Christen1,2, Mohamed Tachrount1,2, Benjamin Lemasson1,3, Regine Farion1,2, Sebastien Reyt1,2, Nicolas Coquery1, Christoph Segebarth1,2, Chantal Remy1,2, Emmanuel Louis Barbier1,2
1Inserm, U836, Grenoble, France; 2Université Joseph Fourier, Grenoble Institut des Neurosciences, UMR-S836, Grenoble, France; 3Oncodesign Biotechnology, Dijon, France
To characterize microvasculature, one can perform a DCE-MRI followed by a DSC-MRI experiment. However, estimates from a DSC experiment performed after a DCE-MRI experiment differ from estimates derived from a single DSC experiment, especially due to different T1. In this study, we investigate how T1 effect contributes to rCBV estimates in the case of one and two consecutive injections of contrast agent (CA). Thus, we used a multi echo spiral sequence in a rat glioma model. Results suggest that DSC-MRI performed during a second injection of CA is less sensitive to T1 effects than DSC-MRI performed during a first injection.
Emelie Lindgren1, Linda Knutsson1, Danielle van Westen2,3, Karin Markenroth Bloch4, Freddy Ståhlberg1,3, Ronnie Wirestam1
1Department of Medical Radiation Physics, Lund University, Lund, Sweden; 2Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; 3Department of Diagnostic Radiology, Lund University, Lund, Sweden; 4Philips Medical Systems, Lund, Sweden
The phase shift during a contrast-agent bolus passage is assumed to be proportional to the concentration of contrast agent. In this study, phase-shift curves in tissue and artery were registered and a phase-based perfusion index and grey-matter MTT were calculated. The relationship between the phase-based perfusion index and ASL CBF estimates showed good linear correlation (r=0.81). The mean grey-matter MTT was 5.4 s, consistent with literature values. Phase-based absolute quantification of CBF is difficult, but the use of a phase-based perfusion index for rescaling of DSC-MRI results can potentially be of value to achieve more robust and reproducible DSC-MRI estimates.
1785. T1-Independent Vessel Size Imaging with Multi-Gradient- And Spin-Echo EPI
Heiko Schmiedeskamp1, Matus Straka1, Diane Jenuleson2, Greg Zaharchuk1, Roland Bammer1
1Lucas Center, Department of Radiology, Stanford University, Stanford, CA, United States; 2Stanford University Medical Center, Stanford, CA, United States
Vessel size imaging is a relatively new technique that relates contrast agent-induced changes of transverse relaxation rates, R2 and R2*, to each other to obtain an index that provides information about the size of vessels within a voxel of interrogation. Ideally, such measurements require the simultaneous acquisition of multiple gradient-echo (GE) and a spin-echo (SE) signals. However, limiting the acquisition to one GE and SE induces T1-related errors in the vessel size estimation. This problem can be solved by acquiring multiple GE/SE-signals, from which one can derive T1-independent estimates of R2 and R2* from before and during contrast-agent passage.
1786. Effects of Blood δR2* Non-Linearity on Absolute Perfusion Quantification Using DSC-MRI: Comparison with Xe-133 SPECT
Linda Knutsson1, Freddy Ståhlberg1,2, Ronnie Wirestam1, Matthias Johannes Paulus van Osch3
1Department of Medical Radiation Physics, Lund University, Lund, Sweden; 2Department of Diagnostic Radiology, Lund University, Lund, Sweden; 3Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
A linear relationship between the δR2* and contrast agent concentration in blood is often assumed, however, calibration measurements in whole blood have shown that a non-linear relation between δR2* and contrast agent concentration exists. In this evaluation of CBF data, we compared absolute CBF obtained using DSC-MRI and Xe-133 SPECT, using both a linear relationship and a non-linear relationship when applying a venous output function (VOF) correction scheme to DSC-MRI data from healthy subjects. The results showed that the observed degrees of correlation were similar when the linear and non-linear relationships were applied to the AIF and VOF from DSC-MRI.
1787. Robust Arterial Input and Venous Output Function Detection for Automatic Processing in DSC-MRI
Matus Straka1, Gregory W. Albers2, Roland Bammer1
1Radiology, Stanford University, Stanford, CA, United States; 2Stroke Center, Stanford University Medical Center, Stanford, CA, United States
Routine acquisition of DSC-MRI PWI datasets highly benefits from full automated post-processing. Selection of arterial input and venous output function is a key step that ensures robustness and reliability of unsupervised processing. A novel method of AIF and VOF selection is proposed by means of tubular filtering and simple analysis of mean temporal signals. Weighting factors the favor arterial and venous signals, as well as vessel orientations are derived. As a result, robustness of AIF and VOF selection was improved.
1788. Joint Estimation of AIF and Perfusion Parameters from Dynamic Susceptibility Contrast MRI in Mouse Gliomas Using a Tissue Model
Kathleen E. Chaffee1, Joshua S. Shimony1, G. Larry Bretthorst1, Joel R. Garbow1
1Radiology, Washington University, Saint Louis, MO, United States
DSC MRI provides valuable perfusion parameters that correlate with brain tumor progression, but requires a difficult to measure arterial input function (AIF). Using a modification of standard tracer kinetics applied to a tissue perfusion model allows both the AIF and residue curve to be determined for each pixel. The parameters are estimated by Bayesian probability theory using Markov chain Monte Carlo simulations to sample the joint posterior probabilities for the parameters. Here we report DSC MRI investigations on a mouse gliomas that demonstrates characteristic perfusion parameters that do not require an independent measurement of an AIF.
1789. Improving and Validating a Local AIF Method
Lisa Willats1, Soren Christensen2, Henry Ma3, Geoffrey Donnan4,5, Alan Connelly1,5, Fernando Calamante1,5
1Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Australia; 2Department of Radiology, University of Melbourne, Australia; 3National Stroke Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Australia; 4Florey Neuroscience Institutes , Melbourne, Australia; 5Department of Medicine, University of Melbourne, Australia
In bolus tracking the perfusion errors associated with bolus delay/dispersion may be minimised using a local Arterial Input Function (AIF) analysis. We improve a previously presented local AIF method by minimising the influence of the Mean Transit Time (MTT) on the local AIF selection. This is particularly important for identifying local AIFs in regions bordering normal and abnormal MTT tissue. We assess the improvement by comparing the amount of delay/dispersion remaining in the deconvolved tissue response after each local AIF approach, and compare both methods with the standard global AIF analysis.
1790. Repeatability of Automated Global and Local Arterial Input Function Deconvolution Methods for Generating Cerebral Blood Flow Maps
Aleksandra Maria Stankiewicz1,2, Ona Wu2, Thomas Benner2, Robert E. Irie2, Tracy T. Batchelor2, A Gregory Sorensen2
1Harvard University, Cambridge, MA, United States; 2Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, United States
Perfusion-weighted Magnetic Resonance (MR) Imaging is used to assess the risk of tissue infarction in acute stroke patients and tumor angiogenesis in cancer patients. We compared circular global arterial input function (AIF) and local AIF algorithms, recently proposed automated methods for MR signal deconvolution. 13 patients with 2 MR scans within 48 hours were studied. The variation between global AIF cerebral blood flow (CBF) maps from the first and second scans was 0.220 ± 0.043, and between local AIF CBF maps was 0.263 ± 0.041 (P-value = 0.0015). Superior repeatability of global AIF-based CBF maps may be important in speedy diagnosis and risk stratification.
1791. Acuracy and Reliability of Post-Processing Software for DSC MR Perfusion: Quantitative Analysis by Digital Phantom Data
Kohsuke Kudo1, Soren Christensen2, Makoto Sasaki1, Matus Straka3, Shunrou Fujiwara1, Kinya Ishizaka4, Yuri Zaitsu4, Noriyuki Fujima4, Satoshi Terae4, Kuniaki Ogasawara5, Leif Ostergaard6
1Advanced Medical Research Center, Iwate Medical University, Morioka, Iwate, Japan; 2Departments of Neurology and Radiology, University of Melbourne, Melbourne, Australia; 3Department of Radiology, Stanford University, CA, United States; 4Department of Radiology, Hokkaido University Hospital, Sapporo, Japan; 5Department of Neurosurgery, Iwate Medical University, Morioka, Iwate, Japan; 6Department of Neuroradiology, Aarhus University Hospital, Aarhus, Denmark
A variety of post-processing programs and algorithms for dynamic susceptibility contrast (DSC) MR perfusion are available; however, the accuracy and reliability of these programs have not been subject to a standardized quality control. We developed digital phantom data set, to evaluate the accuracy and characteristics of quantitative values derived from DSC perfusion analysis software. By using this phantom, we could check tracer-delay dependency for CBF, CBV, MTT, and Tmax, as well as linearity of CBF and MTT against true values.
Valerij G. Kiselev1
1Medical Physics, Dpt. of Diagnostic Radiology, University Hospital Freiburg, Freiburg, BW, Germany
Transverse relaxation in living tissue is contributed by the dephasing of spins due to diffusion in mesoscopic magnetic fields induced, for example, by paramagnetic tracer in the blood pool. The associated correlation time is commensurate with the echo time of typical measurement sequences. Varying the echo time changes the character of dephasing from reversible for short TE to irreversible for long TE. This dependence is quantified by calculating the transverse relaxation rate in the capillary network for multiple refocusing pulses in the static dephasing regime. This yields a modified formula for the mean vessel size in the vessel size imaging.
1793. Equivalence of CBV Measurement Methods in DSC-MRI
Matus Straka1, Gregory W. Albers2, Roland Bammer1
1Radiology, Stanford University, Stanford, CA, United States; 2Stroke Center, Stanford University Medical Center, Stanford, CA, United States
Two widely used methods exist for computing cerebral blood volume (CBV) in DSC-MRI perfusion, using measured signals as well as deconvolved residue function. Some authors claim that these methods do not deliver identical results. We explain that the methods must deliver equivalent results and any difference in obtained values is just caused by signal post-processing errors and wrong interpretation of indicator-dilution theory and convolution theorem. Identity of the two methods is shown in time- and frequency-domains as well as by means of numerical results. Possible sources of the processing errors are discussed and solutions how to avoid those are proposed.
1794. Design of a Data Driven Deconvolution Filter for DSC Perfusion
Philipp Emerich1, Peter Gall1, Birgitte Fuglsang Kjølby2, Elias Kellner1, Irina Mader3, Valerij Kiselev1
1Medical Physics, University Hospital Freiburg, Freiburg, Germany; 2Dept. of Neuroradiology, Arhus University Hospital, Arhus, Denmark; 3Dept. of Neuroradiology, University Hospital Freiburg, Freiburg, Germany
Bolus tracking perfusion evaluation relies on the deconvolution of a tracer concentration time-courses in an arterial and a tissue voxel following the tracer kinetic model. The object of this work is to propose a method to design a data driven Tikhonov regularization filter in the Fourier domain and to compare it to the singular value decomposition (SVD) based approaches using the mathematical equivalence of Fourier and circular SVD (oSVD).
Peter Gall1, Valerij Kiselev1
1Medical Physics, University Hospital Freiburg, Freiburg, Germany
The residue function, R(t), is fundamental for description of microcirculation. To define this function is one of the aims of DSC perfusion MRI. It is found by solving an ill-posed problem, the deconvolution, for which one of approaches is to fit a model R(t) to data. Commonly, phenomenological functional shapes are used to model R(t) respecting only its most general properties. Studies based on ASL indicate insufficiency of this approach. In this work we present a derivation the residue function from the laws of laminar flow and a model for the architecture of the vascular tree.