TRADITIONAL POSTER - ismrm

Poster Sessions
1569. White Matter Model for Diffusional Kurtosis Imaging
Els Fieremans 1 , Jens H. Jensen 1 , Ali Tabesh 1 , Caixia Hu 1,2 , Joseph A. Helpern 1,2
1 Radiology, New York University School of Medicine, New York, United States; 2 Center for Advanced Brain Imaging, Nathan S.
Kline Institute, Orangeburg, NY, United States
We develop an idealized two-compartment diffusion model of white matter suitable for analysis with diffusional kurtosis imaging (DKI). The standard DKI
metrics are used to derive the extracellular and axonal bare diffusion coefficients, the axonal water fraction (AWF), and tortuosity of the extra-axonal
geometry, both providing information related to axonal and myelin density. Values for these parameters obtained for a healthy volunteer agree well with
those of prior studies. Since a DKI dataset is acquired within a few minutes, this approach may allow for the clinical assessment of myelin associated
neuropathologies, such as multiple sclerosis and Alzheimer’s disease.
1570. A Mechanism for Exchange Between Intraaxonal and Extracellular Water: Permeable Nodes of
Ranvier
Markus Nilsson 1 , Håkan Hagslätt 2,3 , Danielle van Westen 2,3 , Ronnie Wirestam 1 , Freddy Ståhlberg 1,3 , Jimmy
Lätt 1,2
1 Department of Medical Radiation Physics, Lund University, Lund, Sweden; 2 Center for Medical Imaging and Physiology, Lund
University Hospital, Lund, Sweden; 3 Department of Diagnostic Radiology, Lund University, Lund, Sweden
The axonal water exchange time was investigated in Monte Carlo simulations using impermeable myelin sheaths, but permeable nodes of Ranvier. The
results showed that axonal exchange times on the sub-second were possible for short and intermediate internodal lengths (i.e. length of the myelin sheath)
and high nodal permeability. This is of importance for high b-value diffusion MRI when measured with different diffusion times.
1571. Renormalization Group Method: Influence of Packing Density of Axons on Diffusivity in Enhanced
Basser-Sen Model of the Brain White Matter
Oleg P. Posnansky 1 , N. J. Shah 2,3
1 Institute of Neuroscience and Medicine - 4, Medical Imaging Physics, Forschungszentrum Juelich, GmbH, 52425 Juelich, Germany;
2 Institute of Neuroscience and Medicine - 4, Medical Imaging Physics , Forschungszentrum Juelich, GmbH , 52425 Juelich, Germany;
3 Deparment of Neurology, Faculty of Medicine, RWTH Aachen University, 52074 Aachen, Germany
Diffusion weighted MRI is sensitive to tissue architecture on a micrometer scale. Determining whether it is possible to infer the specific mechanisms that
underlie changes in the DW-MRI could lead to new diffusion contrasts specific to particular white-matter degeneration processes. We have developed a
renormalization-group method in order to explore the effects of a large range of microparameters on apparent-diffusion and applied it to different kind of
brain tissue tessellations. Our approach takes the influence of disorder into the consideration and it allows quantitative investigation of the sensitivity of
apparent-diffusion to the variations of the dominant set of microparameters.
1572. Observation of Anisotropy at Different Length Scales in Optic and Sciatic Nerve Speciments
Evren Ozarslan 1 , N Shemesh 2 , Y Cohen 2 , Peter J. Basser
1 NIH, Bethesda, MD, United States; 2 Tel Aviv University
Double-PFG MR is a promising method to assess restriction induced anisotropy at different length scales enabling the extraction of information such as
compartment size, shape, and orientation distribution function. In this work, we present the simultaneous characterization of the axon diameter and the
dispersion in the orientation of the axons in excised optic and sciatic nerve specimens. Assuming a von Mises distribution for the orientation distribution
function enabled the characterization of the dispersion of fiber orientations via the estimation of only one additional parameter.
1573. Random Walks in the Model Brain Tissue: Monte Carlo Simulations and Implications for Diffusion
Imaging
Farida Grinberg 1 , Yuliya Kupriyanova 1 , Ana-Maria Oros-Peusquens 1 , N Jon Shah 1,2
1 Medical Imaging Physics, Institute of Neuroscience and Medicine 4, Forschungszentrum Juelich GmbH, Juelich, Germany;
2 Department of Neurology, Faculty of Medicine, RWTH Aachen University, Aachen, Germany
The propagation of water molecules in the brain and the corresponding NMR response are affected by many factors such as compartmentalization,
restrictions, and anisotropy imposed by the cellular microstructure. In addition, interfacial interactions with the cell membranes and exchange play a role.
Therefore, a differentiation between the various contributions to the average NMR signal in in vivo studies represents a difficult task. In this work, we have
performed random-walk Monte Carlo simulations in model systems aiming at establishing the quantitative relations between the dynamics and
microstructure. A detailed analysis of the average diffusion propagators and the corresponding signal attenuations is presented and the implications for
experimental studies are discussed.
1574. Discovering White Matter Structure Beyond Fractional Anisotropy Maps
Jakub Piatkowski 1 , Amos J. Storkey 2 , Mark E. Bastin 3
1 Neuroinformatics Doctoral Training Centre, University of Edinburgh, Edinburgh, United Kingdom; 2 Institute for Adaptive and
Neural Computation, School of Informatics, University of Edinburgh, Edinburgh, United Kingdom; 3 Medical Physics, University of
Edinburgh, Edinburgh, Midlothian, United Kingdom
We use a fully physical two-compartment model, comprising isotropic and anisotropic terms, to describe diffusion MRI data. The posterior distributions
over the parameters of this model are estimated using sampling techniques. This yields maps of white matter (WM) volume, which reveal a level of structure
missing in FA maps. Additionally, we get tensor parameters for the anisotropic compartment (i.e. WM), which provide a measure of fibre-specific
anisotropy that doesn't suffer from partial volume effects.