Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Endogenons Contrast: Relaxation, CEST & MT

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 124

14:00 4484.   Self-Justification Fitting to Improve Reliability of Relaxometry Quantification 
Dan Ma1, Kecheng Liu2, and Mark Griswold1
1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 2Siemens Medical Solution

T1 and T2 quantification have been used for long time in clinical routine diagnosis. Diagnosis relies objectively on absolute T1, T2 quantification rather than subjectively on gray-scaled images. Therefore, the reliability of quantified values should be ensured for clinical diagnosis. In reality, even a slightly system performance imperfection will have big impact on quantified mapping values that may not be seen on gray scaled images. This work introduces a self-justification fitting to improve accuracy of the quantified T2 values due to system imperfections, and to predict the measurable quantification range.

14:30 4485.   Simultaneous Quantification of the Arterial Input Function and Myocardial T1 in Small Animals using Saturation Recovery Look-Locker 
Wen Li1, Bernadette Erowku2, Chris Flask2,3, Mark Griswold1,3, and Xin Yu1,3
1Biomedical Engineering Department, Case Western Reserve University, Cleveland, OH, United States, 2Case Center for Imaging Research, 3Radiology Department

An ECG-triggered saturation recovery Look-Locker (SRLL) method was developed for quantification of arterial input function and contrast agent in heart by fast T1 mapping of the left ventricular blood and myocardium in small animals. Validation study was performed in a two-dose manganese-enhanced MRI experiment. A good correlation was observed between the T1 changes measured by SRLL and the absolute Mn2+ concentration changes measured by atomic absorption spectroscopy. These results suggest that SRLL can provide simultaneous quantification of the arterial input function and myocardial T1 in mouse at high temporal resolution (<3 min).

15:00 4486.   Anatomical brain scans derived from quantitative T1maps: investigation of SNR, CNR and signal uniformity in comparison to conventional methods 
Ulrike Nöth1, Steffen Volz1, and Ralf Deichmann1
1Brain Imaging Center (BIC), Goethe University Frankfurt/Main, Frankfurt/Main, Germany

Standard T1-weighted sequences for anatomical brain imaging generally suffer from signal non-uniformities due to hardware imperfections. In contrast, highly uniform synthetic MR images with arbitrary T1 contrast can be derived from quantitative T1 maps. Purpose of this study was (1) to determine the noise level in quantitative T1 maps with whole brain coverage and 1mm isotropic resolution acquired in about 10min, (2) to calculate synthetic MDEFT and MP-RAGE anatomies with optimum tissue SNR and CNR, and (3) to compare these results with literature values for T1-weighted sequences with the same resolution and similar scan duration.

15:30 4487.   Phantom verification of B1 inhomogeneity correction for 3D-Variable Flip Angle T1 measurements 
Carl Siversson1, Carina Dahlberg2, Carl Johan Tiderius3, Tallal Charles Mamisch4, Jonas Svensson1, and Young jo Kim5
1Department of Radiation Physics, Lund University, Malmö, Sweden, 2Lund Bioimaging center, Lund University, Lund, Sweden, 3Department of Orthopaedics, Lund University, Malmö, Sweden, 4Department of Orthopaedics, University of Bern, Bern, Switzerland, 5Department of Orthopaedics, Children's Hospital Boston, Boston, MA, United States

3D Variable Flip Angle (3D-VFA) is a method for fast 3D T1 quantifications using two successive gradient echo sequences with different excitation pulse flip angles. The 3D-VFA method is sensitive to transmit field B1 variations, which are commonly occurring in vivo. Recently a technique for correcting for such B1 variations, using an additional spin echo type sequence, was introduced. In this work 3D-VFA with and without B1 correction is evaluated using phantoms, in an environment with known B1 variation. It is concluded that the 3D-VFA method with B1 correction generates reliable T1 values even in areas with severe B1 deviation.

Tuesday May 10th
  13:30 - 15:30 Computer 124

13:30 4488.   Spoiling properties of the VAFI method for fast simultaneous T1 and B1 mapping from actual flip-angle imaging (AFI) and variable flip-angle (VFA) data. 
Samuel Anthony Hurley1, Vasily L Yarnykh2, and Alexey A Samsonov3
1Medical Physics, University of Wisconsin, Madison, WI, United States, 2Radiology, University of Washington, Seattle, WA, United States, 3Radiology, University of Wisconsin, Madison, WI, United States

VAFI is a method for fast simultaneous T1 and B1 mapping from actual flip-angle imaging (AFI) and variable flip-angle (VFA) data. It has been shown that a combination of RF and gradient spoiling are essential for accurate T1 quantification, and these issues are investigated for the new VAFI sequence.

14:00 4489.   In vivo correlation of T1 and methemoglobin in a mouse model of deep vein thrombosis 
Prakash Saha1, Marcelo E Andia2, Ulrike Blume2,3, Bijan Modarai1, Matthew Waltham1, Alberto Smith1, Tobias Schaeffter2, and Andrea J Wiethoff2,4
1Department of Academic Surgery, Cardiovascular Division, King's College London, London, United Kingdom, 2Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, 3Philips Healthcare, Best, Netherlands, 4Philips Healthcare, Guildford, United Kingdom

Current imaging methods cannot accurately assess the organization of deep vein thrombosis (DVT). The purpose of this study was to investigate whether the signal generated from MRI can be used to quantify thrombus organization without contrast agent and show that the accumulation of metHb correlates directly with the T1 of the thrombus.

14:30 4490.   Quantitative Model-Based Analysis of Amide Proton Transfer MRI 
Michael A Chappell1,2, Manus J Donahue3, Yee Kai Tee1, Peter Jezzard2, and Stephen J Payne1
1Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom, 2FMRIB Centre, University of Oxford, Oxford, United Kingdom, 3School of Medicine, Vanderbilt University, Nashville, TN, United States

Amide Proton Transfer contrast arises from the exchange of endogenous amide and water protons. The magnitude of the effect depends both on the amide proton concentration and exchange rate, but it is only the latter that relates to pH. In theory it is possible to quantify both concentration and exchange rate using a spectrum sampled at a number of saturation frequencies and model-based fitting. We investigated the feasibility of the approach for in vivo APT using a probabilistic algorithm and a 3-pool model. In 7 healthy subjects estimated exchange rate images were relatively homogenous with an estimated pH around 6.9.

15:00 4491.   CEST Sensitivity Functions Based Sampling Schedule 
Yee Kai Tee1, Michael A Chappell1,2, Jingyi Xie2, and Stephen J Payne1
1Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Oxford Centre for Functional MRI of the Brain, University of Oxford

Quantitative CEST experiments often entail sampling across a range of saturation frequency offsets, the sampling schedule commonly being evenly distributed. Recently, an uneven sampling schedule, which empirically placed samples at key parts of the spectrum and was determined through repeated MR data acquisition, has been shown to be superior. In this work, an optimal sampling schedule which is based on the sensitivity functions of the parameters of interest was sought to improve the precision of parameter estimation. Simulated results indicate that the resulting OSS offers improved accuracy for the estimation of amide proton exchange rate and water centre frequency offset.

Wednesday May 11th
  13:30 - 15:30 Computer 124

13:30 4492.   Enhancement of endogenous CEST effects by optimizing pre-saturation pulse train properties 
Moritz Zaiss1, Benjamin Schmitt1, and Peter Bachert1
1Department of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

Endogenous chemical exchange saturation transfer effects of labile protons localized in small metabolites like amide protons or hydroxyl groups have a small spectral distance from bulk water protons. Therefore, transfer effects are overlapped by the direct water saturation effect, the so called spillover effect, which is eliminated by asymmetry analysis. Short saturation times and duty cycles due to clinical restrictions also distort acquired z-spectra. In this work, these distortions are examined by numerical simulations and phantom studies which lead to an unexpected optimum of the z-spectrum asymmetry for small pulse durations of few ms lowering the pulsed spillover effect.

14:00 4493.   Simulation and optimization of pulsed RF irradiation scheme for chemical exchange saturation transfer (CEST) MRI – demonstration of pH-weighted pulsed-CEST MRI in acute ischemic stroke animal model 
Phillip Zhe Sun1, Enfeng Wang1, Jerry S Cheung1, Thomas Benner1, and A Gregory Sorensen1
1Radiology, Athinoula. A. Martinos Center for Biomedical Imaging, MGH and Harvard Medical School, Charlestown, MA, United States

Chemical exchange saturation transfer (CEST) imaging remains promising for clinical translation. However, CEST contrast also depends on experimental parameters, particularly, RF irradiation power and scheme. Moreover, continuous wave (CW) RF irradiation is not available on most clinical systems due to hardware limitations, for which, the pulsed RF irradiation scheme must be applied instead. Our study quantitatively analyzed and showed that pulsed-CEST provides similar CEST contrast as CW-CEST MRI for slow chemical exchange, while it become less efficient for higher exchange rates. In addition, we confirmed the simulation with pH-weighted pulsed-CEST MRI, both in phantom and in vivo.

14:30 4494.   Center-corrected gagCEST Assessment of Intervertebral Disc Degeneration 
Boyang Zhang1, Xiang Xu1, Jae-Seung Lee1,2, Gil Navon3, Ravinder R. Regatte2, and Alexej Jerschow1
1Department of Chemistry, New York University, New York, NY, United States, 2Department of Radiology, New York University School of Medicine, New York, NY, United States, 3School of Chemistry, Tel Aviv University, Tel Aviv, Israel

The intervertebral disc (IVD) degeneration is an irreversible process, associated with lower back pain. Glycosaminoglycan (GAG) is one of the major components in discs. Changes of [GAG] are believed to indicate the stages of disc degereration. We demonstrate the validation of center-corrected gagCEST approach to assess [GAG] in the disc in vitro. The CEST ratio showed good correlations both with fixed charge density and [N-acetyl], respectively obtained from 23Na and 1H NMR spetra.This method provides a possible solution to detect early degenerated disc. Center-corrected CEST, inspired by the WASSR approach, is essential to obtain reproducible results.

15:00 4495.   Chemical Exchange Saturation Transfer and R1rho dispersions of polypeptides with varying complexities 
Ke Li1,2, Jared G Cobb1,3, Jingping Xie1,2, Zhongliang Zu1,2, Daniel F Gochberg1,2, and John C Gore1,2
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Department of Radiology, Vanderbilt University, Nashville, TN, United States,3Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

Chemical exchange saturation transfer (CEST) imaging techniques have been developed to detect the proton exchange between water and mobile solute molecules which contain exchangeable protons. We hypothesize that CEST contrast and T1ρ relaxation rates are sensitive to the complexity of exchanging molecule and not just the amide content. To test this idea, preliminary studies were performed on a poly-L-Lysine (PLL) model system with different molecular weights, thus different complexities.

Thursday May 12th
  13:30 - 15:30 Computer 124

13:30 4496.   Characterization of iopamidol chemical exchange saturation transfer (CEST) MRI for ratiometric imaging of pH 
Phillip Zhe SUN1, Dario L Longo2, and Silvio Aime2
1Radiology, Athinoula. A. Martinos Center for Biomedical Imaging, MGH and Harvard Medical School, Charlestown, MA, United States, 2Chemistry, IFM and Molecular Imaging Centre, University of Torino, Torino, Italy

Whereas chemical exchange saturation transfer (CEST) MRI is capable of imaging microenvironment pH, the CEST contrast also varies with the labile proton concentration. To solve this confounding factor, ratiometric CEST MRI has been proposed that interrogates CEST effects of multiple distinguishable labile groups so their concentration effect can be normalized. Specifically, iopamidol, a widely used CT agent, has been recently explored for imaging renal pH. Here, we evaluated iopamidol CEST MRI with multi-pool chemical exchange, and showed that both amide and 2-hydrooxypropanamido proton groups are base-catalyzed exchange, suitable for imaging pH from 6 to 7.5.

14:00 4497.   In vivo LipoCEST CA accumulation around U87 mice brain tumor demonstrated by in vivo CEST MRI and ex vivo fluorescence microscopy 
Julien Flament1, Françoise Geffroy1, Boucif Djemaï1, Benoit Theze2, Aline Perrin1, Christelle Medina3, Caroline Robic3, Marc Port3, Franck Lethimonnier1, Gilles Bloch1, Denis Le Bihan1, and Fawzi Boumezbeur1
1NeuroSpin, I2BM, DSV, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France, 2SHFJ, I2BM, DSV, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France,3Guerbet, Research Division, Roissy-Charles de Gaulle, France

LipoCEST are a promising class of contrast agents for MR-based molecular imaging. However, recently similar PEGylated “stealth” paramagnetic liposomes have been shown to be avidly taken up by macrophages. For LipoCEST CA, similar cellular uptake could be extremely detrimental for its detection in vivo. In this study, we injected i.v 10mL/kg b.w. of PEGylated LipoCEST CA with rhodamine on its surface and managed to detect its accumulation around a U87 mice brain tumor in vivo using CEST-MRI. This result constitutes to our knowledge the first visualization of paramagnetic LipoCEST CA after i.v injection confirmed by ex vivo fluorescence microscopy.

14:30 4498.   Optimal parameters for a fixed imaging time acquisition of quantitative magnetization transfer data 
Mara Cercignani1, Gareth J Barker2, and Daniel C Alexander3
1Neuroimaging Laboratory, Santa Lucia Foundation, Rome, Italy, 2CNS, Department of Neuroimaging, King's College London, Institute of Psychiatry, London, United Kingdom, 3Centre for medical image computing, Department of computer science, UCL, London, United Kingdom

In this paper the optimal combination of acquisition parameters (including TR, imaging flip angle, amplitude and offset frequency of the saturation pulses) for quantitative magnetization transfer imaging is obtained by means of the set which gives the maximum precision of the estimated MT parameters, under the constraint of fixed total scan time. The optimisation is achieved for a number of sampling points ranging from 10 to 18 using an algorithm of an "evolutionary" type, and the optimised schemes are compared using numerical simulations and in vivo data.

15:00 4499.   Magnetic field-dependent magnetisation transfer contrast MRI with fast field-cycling 
Chang-Hoon Choi1,2, and David J Lurie1
1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Scotland, United Kingdom, 2MR Solutions Ltd., Guildford, Surrey, United Kingdom

Magnetisation transfer contrast (MTC) MRI is normally implemented at a fixed and high magnetic field (B0) but has only rarely been studied at a range of B0 due to the limitations of available MRI scanners. The use of fast field-cycling with an actively frequency switchable RF coil affords the ability to determine the MT effect over a range of magnetic fields, by rapidly switching B0 in concert with the coil’s resonance frequency. In this work, we used field-cycling to evaluate the MT effects of 1%, 2% and 4% agarose samples at the five different B0 levels by measuring MT ratios.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Endogenons Contrast Relaxometry

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 125

14:00 4500.   Magic angle effects on T2, T2* and T1p relaxation times 
Jiang Du1, Eric Diaz1, Won Bae1, Sheronda Statum1, Nikolaus Szeverenyi1, Darryl DLima2, Graeme Bydder1, and Christine Chung1
1Radiology, University of California, San Diego, San Diego, California, United States, 2Scripps Reseach Institution, San Diego, California, United States

The early stages of OA are associated with breakdown of collagen, decrease in proteoglycans (PG) and increase in water content (1). Recent research has focused on establishing correlations between quantitative MR parameters (T1, T2, T2*, T1ρ) and biochemical or biophysical properties of cartilage. Magic angle effects influence apparent T2 values of tissues with ordered collagen structure, such as articular cartilage, menisci, ligaments and tendons. The purpose of this study was to evaluate the effect of sample orientation on T2/T2* and T1ρ values of the deep radial layer of human patellar cartilage and ligaments.

14:30 4501.   Dynamic changes of on-resonance T1rho dispersion during global ischemia: a 9.4 T study 
Tao Jin1, and Seong-Gi Kim1
1Neuroimaging laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

The spin-lattice relaxation time in the rotating frame (T1rho) has been reported to be a sensitive indicator of cerebral ischemia and can provide complementary MR information of tissue status to water diffusion and perfusion. T1rho is most sensitive to molecular fluctuations with correlation time close to the inverse of the Rabi frequency of the applied spin-locking (SL) pulse. In biological tissue, previous studies have demonstrated that the chemical exchange between bulk water and labile protons of protein or metabolites is an important contributor for the T1rho relaxation in the frequency range of below several kHz. The chemical exchange contrast is related to the difference in the Larmor frequencies of the exchanging protons which increases with the magnetic field strength. Thus, to evaluate whether a large T1rho contrast can be detected at a high magnetic field of 9.4 T and to obtain some insight about the ischemia-induced changes in the tissue microenvironment, we studied the dynamic responses of T1rho during KCL-induced global ischemia for six different SL frequencies.

15:00 4502.   Fluid Suppressed T1lower case Greek rho Mapping of Human Liver on Clinical Scanners 
Anup Singh1, Mohammad Haris1, Kejia Cai1, Walter RT Witschey2, Hari Hariharan1, and Ravinder Reddy1
1CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States, 2Department of Radiology, University Hospital Freiburg, Freiburg, Germany

In the current study, MRI pulse sequence for fluid attenuated T1ρ mapping of human liver on clinical scanner was developed and implemented. Using this technique, we demonstrated the feasibility of single slice T1ρ mapping in a single breath hold on healthy volunteers. T1ρ mapping performed in single breath-hold minimized artifacts related to respiration motion as well as B0 and B1 in-homogeneities. In the normal liver, T1ρ relaxation times were found to be 45-60 ms and 42-48 ms on 1.5T and 3T scanners, respectively. Results from this study show the potential of quantifying biochemical changes in liver pathology using fluid suppressed T1ρ mapping.

15:30 4503.   T1lower case Greek rho Changes in the Human Brain during Respiratory Acidosis and Alkalosis 
Hye Young Heo1, Brian J Dlouhy2, Nader S Dahdaleh2, Daniel R Thedens3, Bradley D Bolster4, John A Wemmie2,5, and Vincent A Magnotta1,3
1Biomedical Engineering, University of Iowa, Iowa City, IA, United States, 2Neurosurgery, University of Iowa, Iowa City, IA, United States, 3Radiology, University of Iowa, Iowa City, IA, United States, 4Siemens Healthcare, Rochester, MN, United States, 5Psychiatry, University of Iowa, Iowa City, IA, United States

The purpose of this study is to assess the ability of magnetic resonance (MR) imaging to measure relative pH changes in vivo. To evaluate pH changes using T1lower case Greek rho imaging, T1lower case Greek rho times were collected for a subject under three conditions: 1) breathing 5% CO2, 2) breathing room air, and 3) hyperventilating. We found that widespread increases in T1lower case Greek rho times during the 5% CO2 condition were consistent with acidosis, whereas reduced T1lower case Greek rho times during hyperventilation were consistent with alkalosis.

Tuesday May 10th
  13:30 - 15:30 Computer 125

13:30 4504.   Age Related Differences in Brain Iron Detected In Vivo at 3T With Quantitative MRI: Comparison of R2, R2' and R2* 
Catherine Anusha Mallik1, David J Lythgoe1, and Gareth J Barker1
1Centre for Neuroimaging Sciences, Institute of Psychiatry, King's College London, London, United Kingdom

Increasing brain iron concentrations are part of the normal aging process, with differences in iron levels between younger and older adults in basal ganglia structures comparable to differences reported in pathological cases (compared to age-matched controls). Using the GESE (Gradient-Echo Spin-Echo) sequence R2, R2' and R2* were measured in two groups (n=6 in each group) of different ages. Significant differences (p <0.05) with age were detected in the substantia nigra for both R2' and R2*. No significant differences in any of the measures were found in white matter.

14:00 4505.   Different patterns of myocardial iron overload by multislice T2* Cardiovascular MR as markers of risk for cardiac dysfunction in thalassemia major. 
Antonella Meloni1, Pasquale Pepe1, Maria Chiara Dell'Amico1, Gennaro Restaino2, Gianluca Valeri3, Massimo Midiri4, Vincenzo Positano1, Petra Keilberg1, Antonio Cardinale5, Massimo Lombardi1, and Alessia Pepe1
1Fondazione G.Monasterio CNR-Regione Toscana and Institute of Clinical Physiology, Pisa, Italy, 2Università Cattolica del Sacro Cuore, Campobasso, Italy, 3Azienda Ospedaliero-Universitaria Ospedali Riuniti "Umberto I-Lancisi-Salesi", Ancona, Italy, 4Policlinico “Paolo Giaccone”, Palermo, Italy, 5Ospedale S Maria alla Gruccia, Montevarchi, Italy

The validated multislice multiecho T2* CMR technique has permitted to quantify segmental and global myocardial iron overload (MIO) detecting different patterns. Biventricular dysfunction is correlated with MIO distribution decreasing from the patients with homogeneous MIO (all segments with T2* values <20 ms) to the patients with no MIO (all segments with T2* values ≥20 ms). Homogeneous MIO and heterogeneous MIO (some segments with T2* values≥20 ms and other segments with T2* values <20 ms) with a global heart T2*<20 predicts a significantly higher risk to develop cardiac dysfunction evaluated by using CMR.

14:30 4506.   Characterization of chelation therapies in thalassemia patients by longitudinal analysis of MRI-assessed cardiac and hepatic iron overload 
Antonella Meloni1, John C Wood2, Alessia Pepe1, Leila J Noetzli2, Maria Chiara Dell'Amico1, Gianluca Valeri3, Claudio Ascioti4, Petra Keilberg1, Massimo Lombardi1, and Vincenzo Positano1
1Fondazione G.Monasterio CNR-Regione Toscana and Institute of Clinical Physiology, Pisa, Italy, 2Children’s Hospital, Los Angeles, United States, 3Azienda Ospedaliero-Universitaria Ospedali Riuniti "Umberto I-Lancisi-Salesi", Ancona, Italy, 4P.O. “Giovanni Paolo II”, Lamezia Terme, Italy

The gradient echo multiecho T2* MRI technique is the most robust method for the sensitive, fast, and reproducible quantification of cardiac and hepatic iron overload in thalassemia patients. Longitudinal analysis of cardiac and hepatic iron overload by regular MRI screening allows the characterization of chelation therapies efficacy and mechanism in thalassemia patients.

15:00 4507.   In Vivo and In Vitro T2* Quantification of Carious Lesions by Ultra-Short Echo-Time (UTE) MRI 
Anna-Katinka Bracher1, Axel Bornstedt1, Erich Hell2, Johannes Ulrici2, and Volker Rasche1
1Department of Internal Medicine II, University Hospital of Ulm, Ulm, Germany, 2Sirona Dental Systems, Bensheim, Germany

The T2* value of dentin and caries lesions was assessed by ultra-short echo time (UTE) MRI. A significant difference between the mean T2* values in caries lesions and healthy dentin was observed. Significant changes in T2* occur even before the lesions become visible in conventional X-ray imaging. This indicates the potential of MRI for very early identification of dental demineralizations and initial caries lesions.

Wednesday May 11th
  13:30 - 15:30 Computer 125

13:30 4508.   Potential Sources for MR Signal Delay 
Yongxian Qian1, and Fernando E. Boada1,2
1Radiology, University of Pittsburgh, Pittsburgh, PA, United States, 2Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States

This work investigates potential sources responsible for MR signal delay we observed and reported before. Computer simulations and phantom studies showed that mobile ions (electrically-charged particles) may be the source for MR signal delay, rather than imperfect performance of the MRI system such as gradient dephasing, B0-field inhomogeneity or chemical shift.

14:00 4509.   Tumor Angiogenesis and Vasculature MRI with Endogenous BOLD Effect 
Kejia Cai1, Adam Shore1, Anup Singh1, Mohammad Haris1, Damodar Reddy1, Hari Hariharan1, Mark Elliott1, and Ravinder Reddy1
1CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

Tumor angiogenesis is the primary facilitator of rapid tumor growth and metastasis. Current MRI techniques using endogenous contrast cannot provide sufficient sensitivity for high-resolution imaging of tumor vasculature. In this study, we use hypoxic challenge to generate sufficient BOLD contrast (~40%), with which high-resolution tumor vasculature maps were able to be obtained. 3D high-resolution tumor vasculature maps can be acquired in minutes. This technique allows us to quantify tumor size, measure tumor vasculature density, provide early detection of tumor metastasis, monitor the effectiveness of cancer treatment drugs, and could potentially characterize tumor grade and aggressiveness.

14:30 4510.   Accelerated Gradient-Recalled Echo, Asymetric Spin-Echo (GREASE-II) for Production of High-Resolution Human T1, T2, and T2* Maps 
Daniel Lee Shefchik1, Andrew Scott Nencka1, Andrzej Jesmanowicz1, and James S Hyde1
1Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States

The gradient-echo asymmetric spin-echo pulse sequence (GREASE) originally allowed for the production of T2 and/or T2* maps. We have modified GREASE to allow simultaneous mapping of T2, T2*, and T1. This was accomplished by accelerating image acquisition by adding partial k-space and generalized autocalibrating partially parallel acquisition (GRAPPA) methods, and utilizing additional excitation and refocusing pulses. These modifications to the original GREASE pulse sequence allow the acquisition of six images following an excitation pulse, enabling the generation of multi-parametric relaxivity maps.

15:00 4511.   Understanding the effects of oriented susceptibility inclusions on the phase and magnitude of gradient echo signals 
Anna Izabella Blazejewska1, Samuel Wharton1, Penny A. Gowland1, and Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom

Magnetic susceptibility differences generate inhomogeneities in the local magnetic field which modulate the magnitude and phase of the signals acquired in MRI. With the advent of susceptibility mapping it has become particularly important to understand the relationship between microscopic structure in the distribution of susceptibility and the induced variation in the NMR frequency. We simulated the field perturbations generated in a uniform matrix containing oriented ellipsoidal inclusions of different susceptibility and used this information to explore the effect of the shape of the inclusions on the phase and magnitude of the MR signal in the "static dephasing" regime.

Thursday May 12th
  13:30 - 15:30 Computer 125

13:30 4512.   Determinants of T2* relaxation in white matter: insights from postmortem analyses 
Christian Langkammer1,2, Nikolaus Krebs2, Walter Goessler3, Eva Scheurer2, Michaela Soellinger1, Kathrin Yen2, Franz Fazekas1, and Stefan Ropele1
1Department of Neurology, Medical University of Graz, Graz, Austria, 2Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria, 3Institute of Chemistry - Analytical Chemistry, University of Graz, Graz, Austria

This study investigated possible contributions of iron deposition, myelin density and fiber orientation on R2* relaxation rates in white matter by using quantitative MRI of postmortem brains in situ and by assessing regional iron concentrations with inductively coupled plasma mass spectrometry. The results suggest that the density of myelin is the dominant determinant of R2* in white matter while the presence of iron additionally has a strong effect. Our results do not support the hypothesis that fiber orientation contributes to the phenomenon of T2* relaxation.

14:00 4513.   Quantitative iron mapping in human brain based on the apparent transverse relaxation time 
Fumiyuki Mitsumori1, Hidehiro Watanabe1, and Nobuhiro Takaya1
1Natl. Inst. Environmental Studies, Tsukuba, Ibaraki, Japan

Iron is an essential element in human body, but its overabundance is toxic through the production of reactive oxygen species. We previously reported that the apparent transverse relaxation rate (R2õ = 1/T2õ) in human brain obtained using a MASE sequence is well explained by a linear combination of the regional non-hemin iron concentration [Fe] and the macromolecular mass fraction fM defined as 1 - water fraction. In the present study we attempted the quantitative iron mapping based on the above relationship between R2õ, [Fe], and fM. Iron distribution in normal brain and that with cavernous hemangioma was successfully visualized.

14:30 4514.   Effects of Fat Particle Size on R2* in Fat-Water-SPIO Emulsion Phantoms: Implications for Fat Quantification with Phantoms 
Catherine D. G. Hines1, Calista Roen1, Diego Hernando1, and Scott B Reeder1,2
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, 2Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, United States

As iron differentially affects the T2* of water and fat, the purpose of this work is to investigate the impact of fat particle size on the behavior of R2* of water and fat for T2* correction for fat quantification. A homogeneous fat-water-SPIO phantom of constant fat-fraction was constructed with varying particle sizes of fat. Phantom results show that in the presence of iron, fat and water have different R2* values, which are highly dependent on fat particle size. Thus, fat particle size impacts the ability of a quantitative MRI method that uses T2* correction to quantify fat, depending on how T2* correction is performed.

15:00 4515.   A Simplified Approach for Anisotropic Susceptibility Map Calculation 
Sam Wharton1, and Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom

Recently, it was shown that the magnetic susceptibility of white matter has measurable anisotropy, but calculation of the full anisotropic susceptibility tensor requires a 6-parameter fit, using phase maps acquired at multiple orientations to B0. Here, we present a method for reducing the parameters in the fitting process to two, based on the assumption of cylindrical symmetry and a priori knowledge of the orientation of the principal axis of the susceptibility tensor. The 2-parameter method is demonstrated on simulated data and shown to require less sampling orientations and a smaller range of rotation angles compared to the 6-parameter method.


Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Novel Tissue Contrast

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 126

14:00 4516.   Orientation and Microstructure Effects on Susceptibility Reconstruction: a Diffusion Phantom Study 
Johannes Lindemeyer1, Ana-Maria Oros-Peusquens1, Ezequiel Farrher1, Farida Grinberg1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen, Aachen, Germany

The influence of parallel fibre structures on the static field and on the observed susceptibility are investigated using a diffusion phantom. A series of measurements at various orientations with respect to B0 and comparative simulations are presented. A bulk-susceptibility appears to be insufficient to represent a parallel fibre area. A simple chequerboard fibre-stacking simulation allowed us to produce good correspondence with observed field shifts.

14:30 4517.   Effect of Orientation of 2D Phase High-Pass Filter on Susceptibility Mapping of Veins and Microbleeds 
Jaladhar Neelavalli1, Saifeng Liu2, YuChung Norman Cheng3, Ewart Mark Haacke1,3, and Zhifeng Kou4
1The Magnetic Resonance Imaging Institute for Biomedical Research, Detroit, Michigan, United States, 2Biomedical Engineering, Mcmaster University, Hamilton, Ontario, Canada, 3Academic Radiology, Wayne State University, Detroit, Michigan, United States, 4Biomedical Engineering, Wayne State University, Detroit, Michigan, United States

We find that the slice orientation in which 2D homodyne high pass filter is applied on phase data strongly influences susceptibility quantification error. This error also varies with the relative orientation of vessels with the main field.

15:00 4518.   Dependence of White Matter Orientation to Magnet Field on Gradient-Echo Imaging at 17.2 Tesla in Mice. 
Christopher John Wiggins1, Denis Le Bihan1, and Luisa Ciobanu1
1LRMN, CEA/NeuroSpin, Gif-Sur-Yvette cedex, France

It has previously been shown in both human and monkey models that the T2* signal of white matter tracts are dependent on their orientation with respect to the applied magnetic field. With the availability of a 17.2 Tesla 26cm bore MRI system, there exists the capability to examine this effect at yet higher fields, while using the higher sensitivity to provide sufficient resolution to use a mouse model. The work presented here confirms the sensitivity of mouse white matter tracts to their orientation relative to the applied field. When the tracts are oriented along the axis of the magnet, the T2* is relatively long compared to when the same tracts are oriented transverse to the applied field.

15:30 4519.   Use of a non-fixed brain tissue sample to examine the effect of white matter orientation to the magnetic field on MRI signals 
Christopher John Wiggins1, and Denis Le Bihan1
1LRMN, CEA/NeuroSpin, Gif-Sur-Yvette cedex, France

It has previously been shown in both human and monkey models that the gradient echo signal of white matter tracts are dependent on their orientation with respect to the applied magnetic field. While in-vivo, both the T2* value and the phase appear to vary with the orientation, ex-vivo studies appear to show only a phase variation. In order both to find a model that allows measurements at multiple orientations, as well as to examine whether the formalin fixation process affects these signals, a sample of non-fixed bovine brain tissue was examined. This showed both T2* and phase variation, similar to in-vivo examinations, indicating that it is the fixation process that alters the T2* behaviour. In addition, T2 (TSE) weighted imaging showed no significant variation with orientation, which thus eliminates a Magic Angle type behaviour.

Tuesday May 10th
  13:30 - 15:30 Computer 126

13:30 4520.   Positive-Contrast Imaging with Phase-Perturbed Differenced SSFP 
R. Reeve Ingle1, and Dwight G. Nishimura1
1Electrical Engineering, Stanford University, Stanford, California, United States

A novel positive-contrast imaging technique is presented and analyzed via Bloch simulation and SPIO phantom imaging. The Phase-Perturbed Differenced SSFP (PDSSFP) sequence is obtained by perturbing alternate RF phases of a bSSFP sequence, yielding an alternating steady-state profile with large signal deviations localized to specific off-resonant frequencies. If acquisitions during even and odd TRs are subtracted, the resulting spectral profile contains signal peaks at these critical frequencies with nulls in between. By aligning the nulls with water and fat resonances, robust background suppression can be obtained while achieving high peak contrast from off-resonant spins.

14:00 4521.   Characterizing Tissue Microstructure Orientation by Multi-Directional Sub-pixel Enhancement of Nonuniform Tissue (SPENT) Sequence 
Bailiang Chen1, Bernard Siow2, David Carmichael3, Freddy Odille2, Roger Ordidge1, and Andrew Todd-Pokropek1
1Medical Physics and Bioengineering, University College London, London, London, United Kingdom, 2Centre for Medical Image Computing, University College London, London, London, United Kingdom, 3Department of Clinical and Experimental Epilepsy, UCL, Institute of Neurology, London, United Kingdom

At different resolution levels, the net appearance of the micro-architecture feature different degrees of tissue homogeneity. This type of information can be revealed by the recently developed SPENT sequence, leading to a quantitative measurement of the direction specific inhomogeniety. When measuring a sufficient number of directions, a preferred direction of underlying structure can be identified by creating a structure tensor. Here a multi-directional SPENT sequence series was developed and applied to a chicken femur to characterize its trabecular bone orientation. The orientation characterization was further validated by applying the methodology to a pineapple sample with an obvious fibre orientation.

14:30 4522.   Macroscopic meets microscopic: the use of Multi Acquisition Variable Resonance Image Combination (MAVRIC) for detection of microscopic objects by means of off-resonance excitation 
Gerrit Hendrik van de Maat1, U A Blume2, C J den Harder2, Clemens Bos3, and Chris J Bakker1
1Image Sciences Institute, University Medical Center, Utrecht, Utrecht, Netherlands, 2MR CTO, Philips Healthcare, Best, Netherlands, 3MR Clinical Science, Philips Healthcare, Best, Netherlands

We investigated the use of Multi Acquisition Variable Resonance Image Combination (MAVRIC), developed for imaging near metallic implants, for detection of microscopic field disturbers by means of off-resonance excited. By using MAVRIC, the whole range of off-resonance frequencies induced by the disturbers can be covered, which increases the sensitivity of off-resonance excitation and offers the opportunity for quantitative measurements. In addition, the anatomical reference information is preserved. The method was demonstrated for the special case of Holmium-166 loaded microspheres but can also be applied to iron-labeled cells or other objects that have a susceptibility that differs from their surroundings.

15:00 4523.   Improving susceptibility weighted contrast using Gradient Echo Plural Contrast Imaging 
Jie Luo1, Bharathi Jagadeesan2, and Dmitriy A Yablonskiy2
1Chemistriy, Washington University in St.Louis, St. Louis, MO, United States, 2Radiology, Washington University School of Medicine, St. Louis, MO, United States

Gradient Echo Plural Contrast Imaging (GEPCI) technique generates co-registered multiple contrast MR images (T1 weighted, quantitative R2*, T2* and frequency maps) with high quality within one scan. In this study, we demonstrate that utilizing basic GEPCI images we can also produce GEPCI-SWI images that are free from T1 weighting and RF field inhomogeneities (characteristic for standard SWI) at the same time providing improved SWI contrast. Combining GEPCI T1w and Frequency map we also generate GEPCI T1F images with superior grey/white matter contrast. This can potentially be used for identifying subtle cortical malformations associated, for example, with venous anomalies.

Wednesday May 11th
  13:30 - 15:30 Computer 126

13:30 4524.   A simple 3D susceptibility model to simulate magnetic field patterns in white matter microstructure 
way cherng Chen1, and Karla Loreen Miller1
1FMRIB, University of Oxford, Oxford, Oxon, United Kingdom

Recent studies of susceptibility-weighted (GRE) imaging have revealed significant heterogeneity in white matter, including dependence on tract orientation to B0. We have developed a 3D susceptibility model that explicitly simulates field patterns generated by tissue microstructure to study potential sources of the observed signal properties. Axons and myelin are modeled as concentric cylinders and oligodendrocytes are modeled as solid spheres using susceptibility values estimated from literature. The frequency distribution obtained from our model provides estimates of the frequency mean and variance (the source of GRE phase and magnitude signals) and highlights the potential information provided by higher-order distribution statistics.

14:00 4525.   Study of Chemical Exchange Effect on Water MR Frequency Shifts using CEST 
Xiang He1, Jie Luo2, Dmitriy A. Yablonskiy2, and Kyongtae Ty Bae1
1Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Mallinckrodt Institute of Radiology, Washington University in St Louis, St Louis, Missouri, United States

We investigated the effect of chemical exchange on water MR frequency through Bloch equation simulation and by in-vivo brain CEST experiment. Bloch equation simulation predicted a very small contribution from slow exchange amide (NH) group proton. The predicted contribution from faster exchange hydroxyl (OH) group, if measured with CEST approach, would also be small. Both statements were confirmed by in-vivo experiment, which found undetectable absolution frequency shift and little change on relative GM/WM frequency contrast by CEST. The effect by hydroxyl groups can only be detected by CEST if the phase evolution profile can be acquired with sub-millisecond echo time.

14:30 4526.   Accurate Determination of Water-Macromolecule Exchange Independent of Reference Interaction 
Tobias Leutritz1, Liane Hilfert2, Karl-Heinz Smalla3, Oliver Speck1, and Kai Zhong1
1Biomedical Magnetic Resonance, Otto-von-Guericke-University, Magdeburg, Germany, 2Institute for Chemistry, Otto-von-Guericke-University, Magdeburg, Germany,3Leibniz-Institute for Neurobiology, Magdeburg, Germany

Water macromolecule exchange (WME) plays an important role in tissue phase contrast. Previous studies using different NMR references gave different results for WME shift compared to the macromolecule susceptibility shift. Here, a systematic study was carried out and showed that the WME shift is on the same order compared to that of the macromolecule susceptibility shift with opposite sign. The commonly used reference compounds, e.g. trimethyl-silyl-propionate (TMSP) and 1,4-dioxane must be used with caution to obtain proper WME and susceptibility values for tissues.

15:00 4527.   Non-linear evolution of GRE phase as a means to investigate tissue microstructure 
Ferdinand Schweser1,2, Andreas Deistung1, Daniel Güllmar1, Marie Atterbury1,3, Berengar Wendel Lehr1, Karsten Sommer1,4, and Jürgen R. Reichenbach1
1Medical Physics Group, Dept. of Diagnostic and Interventional Radiology 1, Jena University Hospital, Jena, Germany, 2School of Medicine, Friedrich Schiller University of Jena, Jena, Germany, 3Dept. of Physics, Brown University, Providence, RI, United States, 4School of Physics and Astronomy, Friedrich Schiller University of Jena, Jena, Germany

Gradient-echo (GRE) magnetic resonance phase data are proportional to the magnetic field, providing useful information for several applications. However, the sources of the phase contrast and their relative contributions to the phase signal are still contentious. In this contribution, we demonstrate and investigate the occurrence of non-linear phase evolution in the human brain.

Thursday May 12th
  13:30 - 15:30 Computer 126

13:30 4528.   In vivo acquisition of CEST MRI using Length and Offset VARiation of Saturation CEST (LOVARS-CEST) for artifact reduction 
Xiaolei Song1,2, Guanshu Liu1,3, Amnon Bar-Shir1,2, Michael Gorelik1,2, Assaf A. Gilad1,2, Peter C.M. Van Zijl1,3, Jeff W.M. Bulte1,2, and Michael T. McMahon1,3
1Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University, Baltimore, MD, United States, 2Cellular Imaging Section, Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, United States, 3F.M. Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States

Chemical Exchange Saturation Transfer (CEST) MRI has been shown to provide additional information for assessing the grade of brain tumors. Most existing CEST acquisitions rely on acquisition of many saturation frequency offsets to correct for B0 inhomogeneities, which is time-consuming and inefficient. We developed a scheme termed Length and Offset VARiation of Saturation (LOVARS-CEST) using saturation pulse length variation combined with FFT post-processing to identify CEST contrast and compensate for field inhomogeneity artifacts. This was tested on mice with 9L brain tumors. The results show that LOVARS-CEST imaging can reduce B0 inhomogeneity artifacts and improve CNR.

14:00 4529.   The removal of blood contributions in phase and susceptibility contrast imaging 
Alexandru Vlad Avram1,2, Arnaud Guidon1,2, Chunlei Liu2, and Allen W Song2
1Biomedical Engineering Department, Duke University, Durham, NC, United States, 2Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States

The emerging phase contrast and susceptibility imaging can be significantly influenced by the susceptibility within the blood pool. We present here a method to reduce and remove blood contributions to the tissue microstructural mapping. Specifically, a flow-compensated diffusion preparation pulse was introduced to eliminate the intravascular blood signal. The extra-vascular effect is intrinsically suppressed by voxel-averaging the dipolar field around the vessel. Given the usual long echo time required for sufficient phase contrast, the insertion of diffusion packet does not increase the overall imaging time. As a result, our method is effective in removing blood contributions in susceptibility contrast imaging.

14:30 4530.   Improving contrast to noise ratio of resonance frequency contrast images (phase images) using bSSFP 
Jongho Lee1,2, Masaki Fukunaga1,3, and Jeff H. Duyn1
1Advanced MRI section/LFMI/NINDS, National Institutes of Health, Bethesda, MD, United States, 2Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States, 3Biofunctional Imaging, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan

Resonance frequency shifts as measured from gradient-echo phase images provide unique detail of the human brain, in particular at high field. Here we demonstrate a new method to improve contrast-to-noise ration (CNR) of phase images using balanced SSFP. GRE and bSSFP sequences were individually optimized for maximum phase CNR and applied to measure contrast between gray and white matter in normal human brain. The results shows that, in limited brain regions, bSSFP provides a 2.85 times increased CNR efficiency at 3 T and a 1.71 times increased CNR efficiency at 7 T.

15:00 4531.   Frequency Mapping without Phase Wraps 
Issel Anne Lei Lim1,2, Jonathan A D Farrell2,3, Craig K Jones2,3, Deepti S Vikram2,3, Carlos Augusto Renjifo4, and Peter C. M. van Zijl2,3
1Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States, 3Neuroscience Section, Division of MR Research, Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, 4The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States

Susceptibility imaging currently employs gradient echo imaging (GRE) to measure local field (frequency) differences from spatial differences in signal phase. We compare single-echo GRE to the WAter Saturation Shift Referencing (WASSR) method, which uses direct water saturation as a function of RF pulse offset frequency to pinpoint spatial differences in resonance frequency. Results from five normal volunteers show comparable frequency shifts at 3T in frequency maps generated from both methods.


Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Image Analysis Advances

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 127

14:00 4532.   An Automated Method for Scan Geometry Planning for MR Knee Imaging 
Xiaodong Tao1
1Imaging Technologies, GE Global Research Center, Niskayuna, New York, United States

Consistent scan plane prescription for MR imaging of knee joint is very important clinically for easy comparison of images across subjects and in serial evaluation of longitudinal exams. Typical workflow requires careful manual slice positioning and suffers from inter-operator variability. We present a novel algorithm for determining the orientation of the knee joint by segmenting the femur bone from a volumetric localizer image. We have incorporated this approach in a clinical MR system and demonstrated its usefulness in automatically obtaining consistent imaging planes across examinations irrespective of subject position.

14:30 4533.   Automated scan prescription for MRI liver scans 
Takao Goto1, and Hiroyuki Kabasawa1
1Global Applied Science Laboratory, GE Healthcare, Hino-shi, Tokyo, Japan

We present a new method of the automatic scan prescription in MRI liver scans. 3D dataset acquired using fast T1 sequence is preprocessed and converted to 2D coronal projection images to avoid the need for complicated and time-consuming 3D segmentation. 2D Active Shape Model is applied to the projection image and the outer shape of the liver is extracted. The scan plane locations are identified from the inferior and superior edges of the outer shape. 38 volunteers and 15 patients data was tested and showed the satisfactory results in the position accuracy and the computation time.

15:00 4534.   Automatic Derivation of Scan Plane Angles along the Vertebral Column of the Human Spine 
Anand Narasimhamurthy1, Akshay Pai1, Vivek Vaidya2, and Uday Patil1
1GE Global Research Centre, Bangalore, Karnataka, India, 2GE Global Research Centre,Bangalore, Bangalore, Karnataka, India

In this work, a methodology for automated planning of oblique axial MRI scans along the vertebral column, using a combined disk and vertebra search algorithm is presented. Cervical, thoracic and lumbar examinations are considered. The validation was done comparing angulations computed automatically by the algorithm with those made by a radiologist. In all sections of spine considered, the average angulation difference was less than 5 degrees, thus demonstrating the robustness of the proposed method.

15:30 4535.   Automated Scan Plane Planning for Spine MRI using 2D Scout Images 
Suguru Yokosawa1, Yo Taniguchi1, Yoshitaka Bito1, Hisako Nagao2, Miki Tachibana2, and Hiroyuki Itagaki2
1Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, Japan, 2Hitachi Medical Corporation, Kashiwa, Chiba, Japan

We propose a faster automated scan plane planning method for the spine using 2D multi-slice orthogonal three-plane scout images. Our algorithm based method uses 2D scout images that can be acquired rapidly. Furthermore, our algorithm can prescribe scan planes faster than other methods that use 3D data due to the smaller 2D data size. We applied our proposed method in experiments with healthy volunteers and compared the automatically defined scan plane positions with those manually defined. The results showed that our method prescribed scan planes quickly and with acceptable accuracy in clinical practice.

Tuesday May 10th
  13:30 - 15:30 Computer 127

13:30 4536.   Effects of Multichannel Transmission on DTI Metrics 
Geng Guangqiang1, Roland Henry2, and Caroline Rae1,3
1Neuroscience Research Australia, Sydney, NSW, Australia, 2Departments of Radiology and Biomedical Imaging, Neurology, and Bioengineering Graduate Group, University of California, San Francisco, United States, 3UNSW, Sydney, Australia

Magnetic resonance imaging (MRI) with multi-transmission of RF pulses achieves a more homogeneous B1 excitation, improves the signal-to-noise ratio and reduces specific absorption rate. This would benefit imaging methodologies sensitive to noise such as diffusion tensor imaging (DTI). In order to verify the improved imaging performance with the multi-transmission of RF, we have quantified the uncertainties of DTI measurements for anisotropy through the bootstrap algorithm. We have proved that the uncertainties of DTI results are consistently reduced with multi-transmission of RF, and this will potentially reduce the necessary scan time and SAR while maintaining the reliability of DTI measurements.

14:00 4537.   Brain tissue segmentation for diffusion tensor imaging (DTI) data using multi-tensor estimation 
Seiji Kumazawa1, Takashi Yoshiura1, Hiroshi Honda1, and Fukai Toyofuku1
1Kyushu Unversity, Fukuoka, Fukuoka, Japan

To study the cortical/subcortical diffusivity in neurological diseases, brain tissue segmentation methods based on DTI data have been proposed. However, in these methods, fiber crossing regions might be misclassified into gray matter region because of denoting low FA values. We present a new brain tissue segmentation method based on DTI data. The features of our method include the conducting of the segmentation in DTI space without any registration, and using multi-tensor estimation for fiber crossing regions. The results of the digital phantom experiment and human DTI data demonstrate that our method was able to perform a reasonable segmentation for brain tissue on DTI data.

14:30 4538.   Improved morphological information using the Dixon technique in conjunction with DWI for detection of bone metastases 
Matthew David Blackledge1, Duncan Brown1, Toni Wallace1, Nina Tunariu1, Martin O Leach1, Dow Mu Koh1, and David J Collins1
1CR-UK and EPSRC Cancer Imaging Centre, Institute of Cancer Research and Royal Marsden Hospital, Sutton, Surrey, United Kingdom

The aim of this technical development was to investigate the use of multiple whole body two point Dixon imaging as method to acquire high quality whole body anatomical images in conjunction with whole body diffusion weighted imaging. Furthermore, we assess the quality of alignment between Dixon images and diffusion weighted images acquired in the same sitting.

15:00 4539.   Diffusion Kurtosis Imaging (DKI) Reconstruction - Linear or Non-Linear? 
Jiachen Zhuo1,2, Jonathan Simon2, and Rao Gullapalli1
1Radiology, University of Maryland School of Medicine, Baltimore, MD, United States, 2Electrical & Computer Engineering, University of Maryland College Park, College Park, MD, United States

Processing for DKI reconstruction originally used nonlinear least squares methods which were inefficient. Faster DKI reconstruction using linear methods have been proposed as a compromise when real time reconstruction is needed. We investigated fitting accuracy of both the linear and nonlinear methods on a clinically relevant short imaging protocol (2 b-values) and compared the generated DTI and DKI parameters to the gold standard (5 b-values). Our results suggest that linear fit for DKI reconstruction with a tensor first approach provides comparable accuracy to nonlinear fit, hence could be the method of choice for faster and more efficient DKI reconstruction.

Wednesday May 11th
  13:30 - 15:30 Computer 127

13:30 4540.   A variational approach to susceptibility estimation that is insensitive to B0 inhomogeneity 
Clare Poynton1,2, and William Wells III1,3
1Computer Science and Artificial Intelligence Lab (CSAIL), MIT, Cambridge, MA, United States, 2Harvard-MIT Division of HST, MIT, Cambridge, MA, United States, 3Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States

In MRI, measurements of the magnetic field contain useful information about the underlying spatial susceptibility distribution, but estimating susceptibility by direct inversion of the field is ill-posed. In addition, bias fields from mis-set shims and non-local susceptibility sources obscure the subtle susceptibility differences of interest. We describe a variational method for susceptibility estimation that is based on the Laplacian operator. Using the Laplacian of the field and the L1 norm, confounding field artifacts are effectively eliminated and sparse solutions that agree well with true susceptibility values are obtained.

14:00 4541.   Differentiation of superparamagnetic iron oxide nanoparticles and air pockets using independent component analysis 
Jason A Langley1,2, Joonsang Lee1,2, Luning Wang1,2, and Qun Zhao1,2
1Department of Physics & Astronomy, The University of Georgia, Athens, GA, United States, 2Bioimaging Research Center, The University of Georgia, Athens, GA, United States

SPIO nanoparticles (SPIOs) create hypointensities in the magnitude image that make detection of SPIOs difficult in vivo. This negative contrast in the magnitude image can be negated by post-processing positive contrast algorithms. Unfortunately, the positive contrast algorithms cannot distinguish between regions with SPIOs and air pockets. In this abstract, we use independent component analysis (ICA) to differentiate regions containing SPIOs and air pockets in a phantom. Three images of the phantom, taken with different combinations of echo times and repetition times, are used in the ICA procedure. Future studies will attempt to verify this method in vivo.

14:30 4542.   USPIOs quantification in brain mice 2D MR images by default field deconvolution 
Delphine Charpigny1, Jean-Christophe Brisset1, Thomas Grenier1, Marlene Wiart1, and Hugues Benoit-Cattin1
1CREATIS, Lyon, France

We propose to assess the USPIOs concentration through the deconvolution of the default field induced by such nanoparticles. We present results obtained at 7T on MR images of brain mice after injection of USPIOs-labeled cells. The obtained results are promising as we estimate the iron concentration to 0.35 mM compared to a theoretical value of O.32 mM.

15:00 4543.   Quantification of different superparamagnetic iron oxide (SPIO) concentrations in diffuse medium using 4.7T Magnetic Resonance Imaging 
Bang-Bon Koo1, Vibhu Sachdev1, and Ronald J. Killiany1,2
1Multimodal Whole Animal Imaging Core, National Emerging Infectious Disease Laboratories Institute Boston University Medical Campus, Boston, MA, United States,2Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, MA, United States

SPIO nanoparticles in nano-molar to micro-molar concentrations can alter the relaxation rates of many nearby tissue water protons thereby making them conspicuous on post contrast enhanced MRI. However, quantifying in-vivo of SPIO enhanced MRI images in a diffusely variant tissue medium have not been adequately addressed: most studies qualitatively point out the regions with high intensity contrasts and examine signal properties by averaging signals. Here, we designed a multi-compartment agarose gel phantom with 2 different SPIO concentrations to simulate the effects of different diffuse levels on SPIO enhanced MRI. Quantitative post processing techniques were then applied for validations of the effects.

Thursday May 12th
  13:30 - 15:30 Computer 127

13:30 4544.   Feasibility of cortical thickness measures in survivors of childhood acute lymphoblastic leukemia 
Wilburn E Reddick1, John O Glass1, Qing Ji1, David C Carver1, and Kevin R Krull2
1Translational Imaging Research, St. Jude Children's Research Hospital, Memphis, TN, United States, 2Epidemiology and Cancer Control, St. Jude Children's Research Hospital, Memphis, TN, United States

The goal of this study was to determine the feasibility of assessing cortical thickness development in survivors of childhood ALL treated without irradiation. We were able to successfully extract average cortical thickness values from regions throughout the brains of 12 childhood cancer survivors using the FreeSurfer software to analyze MPRAGE images acquired at 1.5T demonstrating the feasibility of these measures. Even with this limited sample size, we demonstrated significantly thinner cortex in regions of the frontal and temporal lobes of survivors which were associated with decreased performance in specific neurocognitive domains of attention, working memory, and processing speed.

14:00 4545.   SyN based multimodal investigation on a small cohort of patients affected with Amnesic Mild Cognitive Impairment 
Fabrizio Fasano1, Chiara Ganazzoli1, Simona Gardini1, Fabio Sambataro2, Letizia Concari1, and Paolo Caffarra1
1Department of Neurosciences, Università degli Studi di Parma, Parma, Italy, 2Italian Institute of Technology, Parma, Italy

The recently developed SyN registration method is applied to a multimodal investigation (morphometric + transverse relaxometry based iron content evaluation) on a small cohort of patients affected with Amnesic Mild Cognitive Impairment. The aim of the study is to investigate the early stage of the disease through the help of the attested powerful registration method combined with the multimodality approach potentiality. Our morphometric findings, although not significant at the cluster level, show reasonable differences between the a-MCI group and the control group. On the other hand the relaxometry investigation was not able to find any difference between groups.

14:30 4546.   Comparison of Longitudinal and Cross-sectional Cortical Thickness Measurements 
Kunio Nakamura1, Robert J Fox2, and Elizabeth Fisher1
1Biomedical Engineering, Cleveland Clinic, Cleveland, OH, United States, 2Mellen Center for Multiple Sclerosis Treatment and Research, Cleveland Clinic

Longitudinal change in cortical thickness is clinically relevant in multiple sclerosis and neurodegenerative disorders but difficult to detect. CLADA is a new longitudinal method for the measurement of changes in cortical thickness. CLADA combines MRIs from all time points and creates unbiased subject-specific template before generating a cortical surface model and longitudinally deforming to each MRI. CLADA is evaluated for its reproducibility and compared to a cross-sectional method where each MRI is independently analyzed. Compared to the cross-sectional method, CLADA reduced variability, and the results suggest that CLADA can be used to reliably measure the change in cortical thickness.

15:00 4547.   Cerebellar GM-WM segmentation accuracy in assessing brain atrophy 
Sushmita Datta1, Xiaojun Sun1, and Ponnada A. Narayana1
1Diagnostic and Interventional Imaging, Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States

Cerebellar atrophy is implicated in a number of neurological disorders. Accurate gray matter (GM) and white matter (WM) segmentation of cerebellum is important for accurate assessment of GM and WM atrophies and their correlation with clinical measures. We have developed a fully automated segmentation technique and applied to brain MRI. The segmentation results obtained with our technique were compared with those obtained with SPM, Freesurfer, and FAST. The results suggest the superior performance of our method compared to the other three.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Image Analysis: Noise, Artifact & Parameter Maps

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 128

14:00 4548.   Use of the noise covariance matrix in array coil quality assurance 
Elizabeth Mary Tunnicliffe1,2, Martin John Graves1,3, and Matthew D Robson4
1Department of Medical Physics & Clinical Engineering, Addenbrooke's Hospital, Cambridge, United Kingdom, 2AVIC, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom, 3Department of Radiology, University of Cambridge, Cambridge, United Kingdom, 4OCMR, Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom

The noise covariance matrix of a phased array coil provides information about both the noise level in individual channels and the correlations between channels. It can therefore be useful in quality assurance procedures as these characteristics are liable to change in the case of coil failure. This work presents examples of noise covariance matrices of functioning and failing arrays and suggests quantitative limits, beyond which remedial action may be required.

14:30 4549.   Spatially variable Rician noise in DTI 
Ivan I. Maximov1, Ezequiel A. Farrher1, Farida Grinberg1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

We propose a new algorithm for noise correction in DTI experiments based on the hypothesis of spatially-variable noise fields. Application of the robust estimator followed by Rician correction of the initially assumed Gaussian standard deviation allows us to produce a more stable and precise scheme for the noise evaluation at arbitrary signal-to-noise ratio levels.

15:00 4550.   Validity of the noncentral chi model in multiple-coil systems with noise correlations 
Santiago Aja-Fernandez1, and Antonio Tristan-Vega2
1Universidad de Valladolid, Valladolid, VA, Spain, 2Harvard Medical School, Boston, MA, United States

Noise in the composite magnitude signal (CMS) from multiple-coil systems is usually assumed to follow a noncentral chi distribution. However, this is true only if the variance of noise is the same for all coils, and no correlation exists between them. If the covariance matrix is not diagonal, the distribution of the CMS is not strictly a noncentral chi. It could be modeled as such only if the coefficient of correlation is small enough and effective values are considered. This will imply a reduced effective number of coils and an increased effective variance of noise.

15:30 4551.   Modification of the simulated-multi-image method allows SNR measurement using sum-of-squares reconstruction 
Elizabeth Mary Tunnicliffe1,2, Martin John Graves1,3, and Matthew D Robson4
1Department of Medical Physics & Clinical Engineering, Addenbrooke's Hospital, Cambridge, United Kingdom, 2AVIC, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom, 3Department of Radiology, University of Cambridge, Cambridge, United Kingdom, 4OCMR, Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom

The simulated-multi-image SNR method allows SNR measurement when the usual multi-image method is impractical, for example in vivo. However, it is limited to linear reconstruction methods, which excludes the usual root-sum-of-squares reconstruction mechanism. Here, we show that by using simulated-multi-power images, this method can be extended to be used with root-sum-of-squares reconstructed images. The multi-power image method also has the advantage that it accounts for noise bias in the signal measurement at lower SNR, unlike the usual multi-image method.

Tuesday May 10th
  13:30 - 15:30 Computer 128

13:30 4552.   Roemer reconstruction yields significant SNR gain over Sum-of-Squares @ 7T. 
Anna Andreychenko1, Sjoerd Crijns1, Ingmar Voogt1, Wouter Koning1, Peter Luijten1, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
1University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

The SNR differences between optimal SNR, magnitude SNR and Sum-of-Squares (SoS) signal combination methods for an array of multiple receiver coil are generally thought to be modest. However, at high fields wave propagation effects arise which can significantly degrade SNR in the images reconstructed with the SoS. Here we have demonstrated both, theoretically and experimentally that optimal signal combination at high field (7T) is beneficial as it can considerably increase image SNR whereas at low field (1.5 T) there is no relevant SNR gain.

14:00 4553.   Tissue-Based Intensity Standardization Technique: Application to the ADNI Multi-Centric Dataset 
Nicolas Robitaille1, Abderazzak Mouiha1, and Simon Duchesne1,2
1Laboratoire MEDICS, Centre de Recherche Université Laval Robert-Giffard, Québec, Québec, Canada, 2Radiology Department, Université Laval, Québec, Québec, Canada

Intensity standardization aims at correcting scanner-dependent intensity variations. Most existing techniques aim at matching the input image histogram onto a standard, while we believe the goal should be to match spatially corresponding tissue intensities. In this study, we present STI, a novel technique implementing such approach. We compared STI to an existing histogram-matching method on the ADNI multi-centric dataset by evaluating the mean absolute intensity error (MAE) of the standardized images with respect to the standard, after non-linear registration onto the standard. STI gave better results by showing significantly lower mean MAE for white matter.

14:30 4554.   A New Intensity Inhomogeneity Correction Method for Improved Segmentation of Breast Density on MRI 
Muqing Lin1, Siwa Chan2, Jeon-Hor Chen1,3, Daniel H-E. Chang1, Ke Nie1, Shih-Ting Chen4, Cheng-Ju Lin4, Tzu-Ching Shih4, Orhan Nalcioglu1, and Min-Ying Lydia Su1
1Tu & Yuen Center for Functional Onco-Imaging and Department of Radiological Sciences, University of California, Irvine, CA, United States, 2Department of Radiology, Taichung Veterans General Hospital, Taichung, Taiwan, 3Department of Radiology, China Medical University, Taichung, Taiwan, 4Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan

The purpose is to test a new bias-field correction method by combining N3 (nonparametric non-uniformity normalization) and Fuzzy-C-Means clustering based methods on breast MR images. The new algorithm is based on N3 for an initial correction; then FCM-based correction with smoothing using B-spline surface fitting was repeated iteratively for gradually refined improvements. The results indicated that the N3+FCM correction method performs significantly better than N3 or FCM, and comparable to CLIC. This new bias-field correction method can be implemented to improve the segmentation quality of breast density on inhomogeneous breast MRI, or other images acquired using a surface coil.

15:00 4555.   Joint Restoration of Bi-contrast MRI Data for Intensity Non-uniformities 
Stathis Hadjidemetriou1, Michael Weiner2, and Juergen Hennig1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Department of Radiology, VA UCSF, San Francisco, CA 94121, United States
MRI assumes a uniform static radio-frequency field. However, this is not physically possible and results in an intensity non-uniformity artifact across an image that complicates its further quantitative data analysis. Typically, an acquisition protocol provides images of different contrasts that may suffer from different non-uniformities. This work presents an effective joint intensity uniformity restoration method for two such images. It is performed with Wiener restoration of the auto-co-occurrence and cross-co-occurrence statistics of the images together with several regularity constrains. The effectiveness of the method has been demonstrated with phantom and real brain data.

Wednesday May 11th
  13:30 - 15:30 Computer 128

13:30 4556.   Fuzzy partial volume correction of spinal cord DTI parameters 
Torben Schneider1, David L Thomas2, Carolina Kachramanoglou2, Olga Ciccarelli2, Daniel C Alexander3, and Claudia AM Wheeler-Kingshott1
1Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom, 2Department of Brain Repair & Rehabilitation, UCL Institute of Neurology, London, United Kingdom, 3Centre for Medical Image Computing, Department of Computer Science, UCL, London, United Kingdom

We present a novel correction method for partial volume effects on the estimation of average parameters derived from diffusion tensor imaging in the cervical spinal cord. We demonstrate improved accuracy of our approach in healthy volunteers and demonstrate that our method significantly reduces bias from partial volume effects.

14:00 4557.   Adaptive Iterative T2 Mapping with Maximum Pearson Correlation in the Presence of Noise 
Stephan William Anderson1, Jorge A Soto1, Osamu Sakai1, and Hernan Jara1
1Radiology, Boston University Medical Center, Boston, MA, United States

Purpose: To develop a T2 qMRI algorithm such that the number of echoes used for semi-logarithmic regression is adaptively and iteratively determined on a pixel-by-pixel basis for maximum pixelwise Pearson correlation. Methods: The adaptive iterative T2 algorithm was programmed and used to process CPMG images of mouse liver specimen at 11.7T. Results: T2 maps were generated that provide high anatomical detail as well as high Pearson correlation coefficients across the field of view. Processing time for 16 slices was 90s. Conclusion: Adaptive iterative T2 mapping with short processing times is feasible. This algorithm could be useful for monitoring subtle T2 changes caused by disease in animal models and also for processing in vivo CPMG data.

14:30 4558.   Accurate T2 Mapping with Dual Echo-FSE: Effect of Phase Encoding Profile Orders 
Stephan William Anderson1, Osamu Sakai1, Jorge A Soto1, and Hernan Jara1
1Radiology, Boston University Medical Center, Boston, MA, United States

Purpose: To develop a method for correcting phase encoding profile order effects that can increase the accuracy of T2 qMRI with DE-FSE sequences. Methods: Algorithm incorporating such effects is developed and tested with data of the ACR MRI accreditation phantom and of the brain of a research subject. Results: The correction method leads to T2 values in excellent agreement to those reported with CPMG-32 echoes. Conclusion: Accuracy of T2 qMRI with the DE-FSE pulse sequence can be improved by correcting for profile order effects. This work could have implications for large scale studies using DE-FSE pulse sequences.

15:00 4559.   Elimination of susceptibility-induced distortion in the T2*-decay curve with an improved fitting procedure 
Pei-Hsin Wu1, Nan-Kuei Chen2, and Hsiao-Wen Chung1
1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan, 2Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States

The accuracy of T2* quantification plays an important role in many researches and applications. However, when there exists background susceptibility field gradients, T2* values may be distorted due to TE-shifting effect and echo-shifting effect. In this study, we proposed an improved fitting procedure to quantify the £GTE and £Gky for correcting TE-shifting effect and avoiding signal-loss artifact from echo-shifting effect. Experimental results in the phantom and human brain suggest that the correction scheme proposed in this study has potential to help achieving accurate T2* mapping, particularly at regions with prominent background field gradient.

Thursday May 12th
  13:30 - 15:30 Computer 128

13:30 4560.   Simultaneous T1, T2, and B1 Mapping Using Partially RF-Spoiled Gradient Echo 
Yo Taniguchi1, Suguru Yokosawa1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, Japan

In MR parameter mapping, parameters are estimated from images obtained with various acquisition parameters. For the estimation, the intensity function, which defines the relationship of image intensity to acquisition and MR parameters, needs to be formulated analytically in a simple form. A method to formulate the intensity function numerically by computer simulation based on Bloch equations is proposed. Intensity functions of arbitrary pulse sequences are formulated using this method so that rapid imaging is applied for the mapping. The intensity function for partially RF-spoiled gradient echo was formulated numerically, and we confirmed that T1, T2, and B1 maps were well estimated simultaneously from images obtained in a phantom experiment.

14:00 4561.   A Simplified Nonlinear Fitting Strategy for Estimating T1 from Variable Flip Angle Sequences 
Joshua Trzasko1, Petrice M. Mostardi1, Stephen J Riederer2, and Armando Manduca1
1Mayo Clinic, Rochester, MN, United States, 2Mayo Clinic

Variable flip angle SPGR imaging, despite challenges due to transmit field inhomogeneities, remains a widely used strategy for T1 mapping. Nonetheless, there has been little work on numerical strategies for computing T1 values from such image series, and most estimations are performed using either a two-parameter nonlinear least squares fitting, which is accurate but computationally intensive, or a linear regression approximation, which is significantly faster but prone to error. In this work, we describe a simple numerical optimization strategy which can accelerate NLLS computation by over an order of magnitude without compromising its accuracy.

14:30 4562.   Strong Regularization for Brain Myelin Water Quantification in T2 Relaxation MRI Obtained in 3.0 T 
Qing Ji1, Junyu Guo1, John O. Glass1, and Wilburn E. Reddick1
1Radiological Science, St.Jude Children's Research Hospital, Memphis, TN, United States

Quantification of myelin water fraction (MWF) involves the calculation of the T2 distributions of relaxation spectra using a regularized non-negative least square (NNLS) algorithm. Simulated and experimental T2 decay data were used to investigate the influence of the NNLS regularization on the MWF calculation. The relationship between the MWF and regularization is a “V’ shape curve. The regularization which gave the most accurate and stable agreement with the simulated data was on the strong side of the curve in contrast to previous studies which suggested a weak regularization. Use of the stronger regularization was demonstrated for in vivo data.

15:00 4563.   A Pixel is an Artifact: On the Necessity of Zero-filling in Fourier Imaging 
Xiaolu Zhu1, Boguslaw Tomanek1, and Jonathan Sharp1
1Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, AB, Canada

Pixels visible as small square patches of uniform intensity do not represent object structures – and are therefore artifacts. To quantitatively evaluate this we designed a Fourier-based method to decompose a pixelated visual scene into two parts: one representing the information in the original MRI k-space data, and the other the visible structure related to pixelized patchwork display. Results show that pixelized patchwork displays: A) attenuate actual high spatial frequency content (because patchwork display enforces image uniformity within each patch); and B) introduce artifactual high spatial frequencies (the patch edges). The solution is to zero-fill until individual pixels become invisible.