TRADITIONAL POSTER - ismrm

Poster Sessions
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 intra- and extra-cellular compartments, we show that beading and increased
permeability can act in concert to produce increased perpendicular diffusion. However, while parallel diffusion is decreased by beading, non-Gaussian
behavior is mitigated by increased permeability. This study may aid the development of contrasts specific for axonal injury.
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.
1568. A New Approach to Structural Integrity Assessment Based on Axial and Radial Diffusivities.
Claudia Angela Michela Wheeler-Kingshott 1 , Olga Ciccarelli 2 , Torben Schneider 1 , Daniel C. Alexander 3 ,
Mara Cercignani 4
1 NMR Unit, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom; 2 NMR Unit, Department of
Brain Repair and Rehabilitation, UCL Institute of Neurology, London, United Kingdom; 3 Dept. Computer Science, UCL, Centre for
Medical Image Computing, London, United Kingdom; 4 Neuroimaging Laboratory, Fondazione Santa Lucia, Rome, Italy
A new definition of projected-axial (d p-ax ) and radial (d p-rad ) diffusivities in standard space has been tested in multiple sclerosis and healthy subjects using
VBM. For each subject, d p-ax and d p-rad are defined as the components of the diffusion tensors (DTs) along the most probable direction of healthy tracts as
defined by the eigenvectors of a “super-DT” dataset in standard space (calculated as the average of the DTs of a reference group of healthy subjects). The
results show that in a patient with moderate disability there are areas of reduced d p-ax not revealed by the principal eigenvalue of the DT.