TRADITIONAL POSTER - ismrm

Poster Sessions
1581. On the Influence of the Temporal Gradient Profile on the Apparent Diffusion Coefficient in the
Motional Narrowing Regime in Closed Geometries
Frederik Bernd Laun 1 , Bram Stieltjes
1 Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Baden-Württemberg, Germany
In DWI, the apparent diffusion coefficient is determined by both, the diffusion process and the temporal profile of the diffusion gradients. In this work a
technique to determine the influence of the temporal gradient profile on the measured ADC is developed for the motional narrowing regime in closed
geometries. It yields a direct series expansion in powers on inverse time. It is shown that the discontinuities and integrals over the derivatives of the gradient
profile determine the constants of this series expansion.
1582. Unifying Transverse Relaxation and Diffusion: An Effective Medium Approach
Dmitry S. Novikov 1 , Valerij G. Kiselev 2
1 Radiology, NYU School of Medicine, New York, NY, United States; 2 Medical Physics, Diagnostic Radiology, Uniklinikum
Freiburg, Freiburg, Germany
MR signal is massively volume-averaged. Which parameters of tissue microstructure can survive this averaging, and be quantified by MRI? An answer is
given by the effective medium description of tissues yielding the voxel-averaged equation for the magnetization. Heterogeneous diffusivity, relaxation rate
and Larmor frequency offset give rise to corrections to the magnetization dynamics. The quantifiable tissue parameters are the distinct length scales on
which the local diffusivity, relaxation rate and Larmor frequency vary. The effective medium approach unifies diffusion and relaxation, focussing on the
single quantity whose frequency and wavevector dependence contains all measurable information about tissue heterogeneity.
1583. Estimating Model Uncertainty When Fitting Multiple B-Value Diffusion Weighted Imaging
Matthew R. Orton 1 , David J. Collins 1 , Dow-Mu Koh 2 , Michael Germuska 1 , Martin O. Leach 1
1 CR-UK and EPSRC Cancer Imaging Centre, Institute of Cancer Research, Sutton, Surrey, United Kingdom; 2 Department of
Radiology, Royal Marsden NHS Foundation Trust, Sutton, Surrey, United Kingdom
Many models have been proposed for describing diffusion-weighted data, but as the environment of the diffusion process is known to be very complex in
biological systems, choosing an appropriate model is difficult. We present a Bayesian methodology for estimating the posterior probability (uncertainty) of
a given selection of diffusion models, applied to clinical DWI data. This is of interest to indicate statistical model uncertainty, and therefore uncertainty in
the interpretation of the data. By penalising over complicated models, this methodology provides diffusion metrics that are more stable, and therefore more
sensitive to a wider range of treatment effects.
1584. DWI Signal from a Medium with Heterogeneous Diffusivity
Dmitry S. Novikov 1 , Valerij G. Kiselev 2
1 Radiology, NYU School of Medicine, New York, NY, United States; 2 Medical Physics, Diagnostic Radiology, Uniklinikum
Freiburg, Freiburg, Germany
We consider the DWI signal from any medium (tissue) in which the diffusion coefficient varies in space. Using recently developed effective-medium
approach, we relate the signal to the diffusivity correlation function. Explicit formulas for time-dependent diffusion coefficient and diffusional kurtosis are
provided in the case when the local diffusivity varies on a well-defined length scale. Our results are numerically confirmed by the Monte-Carlo simulation of
diffusion in a two-dimensional model tissue. While the DWI signal has an approximately biexponential form, it is shown to be qualitatively different from
that of the two-compartment exchange (Kärger) model.
1585. From Single- To Double-PFG: Gleaning New Microstructural Information in Complex Specimens
Noam Shemesh 1 , Evren Özarslan 2 , Peter J. Basser 2 , Yoram Cohen 1
1 School of Chemistry, Tel Aviv University, Tel Aviv, Israel; 2 Section on Tissue Biophysics and Biomimetics, NICHD, National
Institutes of Health, Bethesda, MD, United States
Although single-pulsed-field-gradient (s-PFG) methodologies such as DTI and the q-space approach are widely used to probe tissue microstructures, they
suffer from inherent limitations, especially when specimens are characterized by randomly oriented compartments or size distributions. The double-PFG (d-
PFG) is emerging as a new probe for novel microstructural information that cannot be achieved by other means. Here we demonstrate that d-PFG can be
used to extract accurate compartment dimensions at low q-values both in phantoms and in biological cells which are randomly oriented, and in optic and
sciatic nerves. The d-PFG may become an important MRI method in the CNS.
1586. New Quantitative Indices for DWI of the Brain Tissue at High B-Values
Farida Grinberg 1 , Ezequiel A. Farrher 1 , Joachim Kaffanke 1 , Ana-Maria Oros-Peusquens 1 , N. Jon 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
Diffusion MRI permits non-invasive probing of tissue microstructure and function and provides invaluable information in brain diagnostics. Conventional
methods, however, are designed to retrieve only the average diffusion characteristics and tend to ignore deviations from simple Gaussian behaviour.
Recently, increasing efforts have been dedicated to the development of the advanced approaches capable of capturing more detailed information on the
propagation mechanisms. In this work, we report an in vivo diffusion study of the brain based on a detailed analysis of the attenuation patterns. New
quantitative indices are suggested as map parameters and their potential use with respect to studies of the brain is discussed.