Traditional Posters: Diffusion & Perfusion - ismrm

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.
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.