ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: Relaxation Based Contrast

Tuesday, May 10, 2016
Room 334-336
16:00 - 18:00
Moderators: Wenbo Li, Charles Springer

Multiparametric MRI Characterization of Magnetic Viral Complexes
Alexander Joos1, Olga Mykhaylyk2, Norbert Löwa3, Dietmar Eberbeck3, Bernhard Gleich1, and Axel Haase1
1Zentralinstitut für Medizintechnik der Technischen Universität München, Garching, Germany, 2Department of Experimental Oncology, Klinikum rechts der Isar der TU München, Munich, Germany, 3Physikalisch-Technische Bundesanstalt, Berlin, Germany
Magnetic nanoparticles can be used for magnetic drug targeting while MRI can serve as non-invasive therapy monitoring. We investigated the influence of the assembling of magnetic nanoparticles with oncolytic viruses and their uptake into cancer cells on the MRI relaxivities r1, r2 and r2* and magnetically characterized all samples using magnetic particle spectroscopy. Our results show that R2* measurements seem most suitable for particle quantification while R2 is sensitive to the uptake of the particles into the cells. Magnetic particle spectroscopy proves to be an important validation technique for MRI relaxometry.

Fast Quantitative T2 Mapping using Simultaneous-Multi-Slice and Model-Based Reconstruction
Tom Hilbert1,2,3, Jennifer Schulz4, Lauren J. Bains4, José P. Marques4, Reto Meuli2, Jean-Philippe Thiran2,3, Gunnar Krueger2,3,5, David G. Norris4, and Tobias Kober1,2,3
1Advanced Clinical Imaging Technology (HC CMEA SUI DI BM PI), Siemens Healthcare AG, Lausanne, Switzerland, 2Department of Radiology, University Hospital (CHUV), Lausanne, Switzerland, 3LTS5, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 4Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, Netherlands, 5Siemens Medical Solutions USA, Inc., Boston, MA, United States
Long acquisition times of quantitative magnetic resonance imaging (qMRI) are one obstacle that prevents qMRI to be used in clinical routine. Acceleration methods, such as simultaneous-multi-slice and model-based iterative reconstruction proved in the past to allow high acceleration factors in MRI. Here we suggest combining these two methods to allow fast quantitative T2 mapping, yielding a high-resolution (0.7x0.7x3mm³) whole brain (40 slices) acquisition within a clinically acceptable acquisition time of less than 3 minutes. T2 values of the proposed method are similar to the values of the standard method as it is shown on phantom experiments.

A robust T1?-mapping method for in-vivo glucose detection at 7T whole-body scanners
Patrick Schuenke1, Moritz Zaiss1, Christina Koehler2, Alexander Radbruch2,3, Mark Edward Ladd1, and Peter Bachert1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 2Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany, 3Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
Recently it was demonstrated that on–resonant chemical–exchange–sensitive spin–lock (CESL) allows to observe the uptake of administered D–glucose in vivo and thus could be used for glucose metabolism studies. However, conventional spin–lock produces artifacts owing to B1–field inhomogeneities, which are a common problem especially at high-field whole-body MR scanners. Therefore we developed an adiabatic water–T mapping sequence which outperforms conventional spin-lock sequences with respect to its insensitivity to B1–inhomogeneities; its sensitivity to glucose in the millimolar range as well as its applicability to in vivo studies is proven.

Imaging Subcortical White Matter by High Resolution 7 T MRI in vivo: Towards Potential U-Fiber Density Mapping in Humans - Permission Withheld
Evgeniya Kirilina1,2, Juliane Dinse1, Pierre-Louise Bazin1, Carsten Stueber3,4, Stefan Geyer1, Robert Trample1, Andreas Deistung5, Juergen R Reichenbach5, and Nikolaus Weiskopf1,6
1Neurophysics, Max Plank Institute for Human Cognitive and Brain Science, Leipzig, Germany, 2Neurocomputation and Neuroimaging Unit, Department of Educational Science and Psychology, Free University Berlin, Berlin, Germany, 3Department of Radiology, Weill Cornell Medical College, New York, NY, United States, 4Department of Neurology, Yale School of Medicine, Yale University, New Haven, CT, United States,5Medical Physics Group, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 6Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom
Subcortical white matter (SWM) incorporates U-fibers, the intra-hemispheric connections between adjacent gyri. Despite their importance for cortical connectivity little is known about the U-fiber distribution in humans due to the lack of appropriate imaging methods. Herein we investigate SWM using high-resolution in-vivo MRI at 7T. A clear-cut discrimination of SWM from the adjacent brain regions was obtained based on higher qR2*, qR2 and susceptibility in-vivo. These new findings may pave the way for future in-vivo segmentation strategies for this crucial brain region as well as potential U-fiber density mapping in humans.

Mapping orientation dependent and independent components of R2star in the human white matter - an in vivo study - Permission Withheld
Diana Khabipova1,2, Rita Gil2, Marcel Zwiers2, and José Pedro Marques2
1CIBM-AIT, EPFL, Lausanne, Switzerland, 2Centre for Cognitive Neuroimaging, Donders Institute, Nijmegen, Netherlands
Anisotropic microstructure of the white matter causes the apparent transverse relaxivity, $$$R_2^*$$$, to depend on the orientation of white matter fibres in respect to the applied magnetic field. Using the fibre orientation prior knowledge from DTI orientation dependent $$$R_{2,ANISO}^*$$$ and independent $$$R_{2,ISO}^*$$$ components of $$$R_2^*$$$ were calculated. For all studied WM fibres a consistency for the (an)isotropic components between both hemispheres was present. The isotropic component showed higher variability compared to the anisotropic component.

Gradient echo signal decay of bone material at high field requires a gaussian augmentation of the mono-exponential model for T2* determination
Weiqiang Dou1 and Arend Heerschap1
1Radiology, Radboud University Medical Centre, Nijmegen, Netherlands
Previously reported T2*quantification for calcium phosphate cement (CPC), a widely used bone material, remained unsatisfactory with a mono-exponential (ME) fit. A recently proposed Gaussian augmentation of the mono-exponential (GAME) model was reported to have robust fit for gradient echo (GRE) signals. To accurately evaluate GRE-signal decay of CPC, GAME and ME fits were applied in this study for multi-echo time GRE signals acquired at 11.7T. Compared to ME, GAME showed optimal fitting with significantly smaller sum of squared errors and larger R-squared values. Therefore, GAME model is demonstrated to be suitable for GRE signal modeling in CPC at ultra-high field.

Simultaneous estimation of reversible and irreversible transverse relaxation rates in the basal ganglia at 7T: implications for brain iron deposition studies
Mukund Balasubramanian1,2, Jonathan R. Polimeni2,3, and Robert V. Mulkern1,2
1Department of Radiology, Boston Children's Hospital, Boston, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States
Reversible and irreversible transverse relaxation rates were measured at 7T, using the GESSE pulse sequence, in basal ganglia structures in 11 volunteers (ages: 23-81 years). We found that, with a judicious choice of echo times, irreversible rates (R2) in the globus pallidus were conspicuous for all subjects. Furthermore, both reversible and irreversible rates increased with age in a manner consistent with prior postmortem studies of iron concentration in these structures. Since these rates are differentially affected by field perturbations at different spatial scales, their consideration may provide information about the microscopic and mesoscopic distribution and concentration of iron in tissue. 

A General Solution for Transverse Signal Decay Under the Weak Field Approximation: Theory and Validation with Spherical Perturbers
Avery J.L. Berman1,2 and Bruce Pike2
1Montreal Neurological Institute, McGill University, Montreal, QC, Canada, 2Department of Radiology and Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
This study presents a closed-form analytical solution that describes transverse signal relaxation using the weak field approximation (WFA). The closed-form solution (CFS) fully describes the net signal dynamics under any train of 180° refocusing pulses, and we show that it is in close agreement with a commonly employed mono-exponential expression of the WFA. We compared the CFS to simulations from a medium containing spherical perturbers, with a focus on modelling red blood cells. The CFS and simulations were in close agreement but the results systematically varied depending on whether or not the spheres were allowed to overlap. This theory can be applied in areas such as tissue iron imaging or relaxometry of blood.

Rotating frame MRI in human subjects with Multiple Sclerosis
Silvia Mangia1, Alena Svatkova2,3, Peter Bednarik1,3, Igor Nestrasil2, Lynn E. Eberly4, Adam Carpenter5, and Shalom Michaeli1
1Radiology, CMRR, University of Minnesota, Minneapolis, MN, United States, 2Department of Pediatrics, University of Minnesota, Minneapolis, MN, United States, 3Central European Institute of Technology, Masaryk University, Brno, Czech Republic, 4Division of Biostatistics, University of Minnesota, Minneapolis, MN, United States, 5Neurology, University of Minnesota, Minneapolis, MN, United States
Rotating frame MRI methods including adiabatic T1ρ, T2ρ, and RAFF4 were here employed for characterizing the white matter (WM) of relapsing-remitting Multiple Sclerosis (MS) patients. We calculated relaxograms from subcortical WM of MS patients (excluding lesions) and age-matched controls, and compared them with histograms of DTI outcomes. T1ρ, T2ρ and TRAFF4 were significantly different in the WM of MS patients vs controls, while DTI outcomes did not detect group differences. These findings are supported by recent validation studies using demyelination/dysmyelination animal models, where RAFF4 exhibited exceptional ability to probe myelin content/integrity which we attribute to enhanced sensitivity to slow/ultra-slow motion.

R2’ is the Best Transverse Relaxation Rate for Oxygenation Mapping: Experience in Moyamoya Disease with Acetazolamide Challenge
Wendy Ni1,2, Thomas Christen2, and Greg Zaharchuk2
1Department of Electrical Engineering, Stanford University, Stanford, CA, United States, 2Department of Radiology, Stanford University, Stanford, CA, United States
Transverse MR spin relaxation rates, R2*, R2 and R2’ have all been considered sensitive to brain tissue oxygenation.  In this study, we focus on a cohort of pre-operative Moyamoya disease patients and simultaneously map all three rates in addition to cerebral blood flow, both before and after the injection of the vasodilatory drug, acetazolamide.  We found our measurements to be consistent with physiology and previous studies, and to support the use of R2’ for oxygenation mapping instead of R2* and R2.

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