Traditional Posters: Diffusion & Perfusion - ismrm

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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 Peng 1 , Jewell Thomas 1 , Joseph Mettenburg 2 , Avi Snyder 1 , Tammie Benzinger 2 , David Clifford 1 , Robert Paul 3 , Beau Ances 4 1 Neurology, Washington University in St. Louis, St. Louis, MO, United States; 2 Radiology, Washington University in St. Louis, St. Louis, MO, United States; 3 Psychology, University of Missouri St. Louis, St. Louis, MO, United States; 4 Neurology, 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 Keller 1,2 , Aaron Michael Rulseh 1 , Michael Syka 1 , Josef Vymazal 1 1 Nemocnice Na Homolce, Prague, Czech Republic; 2 3rd 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. Diffusion: White Matter Modeling Hall B Tuesday 13:30-15:30 1561. Optimized Diffusion MRI Protocols for Estimating Axon Diameter with Known Fibre Orientation Torben Schneider 1 , Henrik Lundell 2,3 , Tim B. Dyrby 2 , Daniel C. Alexander 4 , Claudia Angela Michela Wheeler-Kingshott 1 1 NMR Unit, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom; 2 Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark; 3 Department of Excercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark; 4 Centre 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 Weng 1,2 , Wen-Yih Iascc Tseng 1,3 1 Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2 Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan; 3 Department 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 Fonteijn 1 , Matt G. Hall 1 , Daniel C. Alexander 1 1 Computer 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 Morgan 1 , Rexford D. Newbould 2 , Brandon Whitcher 2 , Daniel C. Alexander 1 1 Centre for Medical Image Computing, University College London, London, United Kingdom; 2 Clinical 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. Cisternas 1 1 Engineering 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 Farrell 1,2 , Bennett A. Landman 3,4 , Jiangyang Zhang 1 , Seth A. Smith 5,6 , Daniel S. Reich 1,7 , Peter A. Calabresi 8 , Peter C.M. van Zijl 1,2 1 Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 2 Kennedy Krieger Institute, F.M. Kirby Research Center for Functional Brain Imaging, Baltimore, MD, United States; 3 Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 4 Electrical Engineering, Vanderbilt University, Nashville, TN, United States; 5 Dept. of Radiology, Vanderbilt University, Nashville, TN, United States; 6 Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; 7 Neuroimmunology Branch (NINDS), National Institutes of Health, Bethesda, MD, United States; 8 Dept. 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 intraand 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. 1567. Diffusion MRI on Undulating Versus Straight Axons: Reduced Fractional Anisotropy and Increased Apparent Axonal Diameter Håkan Hagslätt 1,2 , Markus Nilsson 3 , Henrik Hansson 3 , Jimmy Lätt 1,3 , Danielle van Westen 1,2 1 Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; 2 Department of Diagnostic Radiology, Lund University Hospital, Lund, Sweden; 3 Department 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.
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Traditional Posters: Diffusion & Perfusion - ismrm

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