TRADITIONAL POSTER - ismrm

Poster Sessions
1627. A Novel Robust Algorithm to Correct for Eddy Current Distortions in High B-Value Diffusion MRI
Henrik Hansson 1 , Jimmy Lätt, 12 , Freddy Ståhlberg 1,3 , Markus Nilsson 1
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
Eddy currents distort diffusion-weighted images, which give rise to artefacts in the estimated apparent diffusion coefficient and the diffusion kurtosis.
Current correction methods are not effective for b-values greater than 1000 s/mm2. We have developed a correction algorithm based on comparison of all
images in an image set, instead of separate volumes. This allows model based distortion correction by maximizing the local correlation of the entire image
set.
1628. Rapid Automated QA for Diffusion MRI
Adriaan L. Moerland 1 , Elizabeth A. Moore 2
1 Advanced Development, Philips Healthcare BV, Best, Netherlands; 2 MR Clinical Science, Philips Healthcare BV, Best, Netherlands
Diffusion MRI is increasingly important in clinical radiology, however the technique is very sensitive to system defects in the gradient chain. A new method
has been developed for easy QA in diffusion MRI. The acquisition is 3 fast DTI scans on a spherical aqueous phantom, taking less than 3 minutes. Analysis
is fully automated and derives measures of deformation of the circular phantom image as well as apparent diffusion coefficient ADC and fractional
anisotropy FA values. Two of the deformation measures were found to be highly sensitive to gradient defects such as eddy current (mis)calibration.
1629. Optimizing Accuracy and Precision in High Resolution Diffusion Tensor Imaging of the Ex Vivo Rat
Heart
Patrick William Hales 1 , Rebecca Burton 2 , Christian Bollensdorff 2 , Jurgen E. Schneider 1
1 Cardiovascular Medicine, Oxford University, Oxford, Oxon, United Kingdom; 2 Physiology, Anatomy & Genetics, Oxford
University, Oxford, Oxon, United Kingdom
The influence of both SNR and diffusion gradient sampling scheme on the precision and accuracy of high resolution (203 μm) DTI data acquired in the ex
vivo rat heart has been investigated. We demonstrate how the use of reduced encoding of diffusion weighted images using the approximate generalized
series reconstruction technique can increase SNR without increasing scan time, and how this can be employed to reduce the overall error in the primary
eigenvector orientation.
1630. About the Origins of Diffusion-Weighting Due to the Non-Linear Phase Dispersion Induced by
Frequency-Swept Pulses
Julien Valette 1,2 , Denis Le Bihan 2 , Franck Lethimonnier 2
1 CEA-MIRCen, Fontenay-aux-Roses, France; 2 CEA-NeuroSpin, Gif-sur-Yvette, France
It has been recognized in the past that the non-linear phase induced by frequency-swept pulses may cause diffusion-weighting. In the present work, the
origins of the non-linear phase dispersion induced by frequency-swept pulses are revisited, in order to assess whether the phase variation of the B1 field
during the sweep should be explicitly considered when calculating diffusion weighting. Following this analysis, an analytical expression is derived for
diffusion-weighting induced by a pair of slice selective hyperbolic secant pulses, and confronted to numerical simulation of the Bloch equations including
diffusion.
1631. On the Accuracy of Diffusion Models for Fast Low-Angle Short-TR SSFP-Echo (FLASH-DW SSFP)
Oliver Bieri 1 , Carl Ganter 2 , Klaus Scheffler 1
1 Radiological Physics, University of Basel Hospital, Basel, Switzerland; 2 Department of Diagnostic Radiology, Technical University
Munich, Munich, Germany
Several models have been developed for the description of diffusion in steady-state free precession (SSFP) sequences. For clinical practice, high SNR and
short acquisition times are desirable with DW-SSFP. In this work, a new approach for quantitative diffusion imaging is proposed using a fast low-angle
short-TR (FLASH) diffusion-weighted (DW) SSFP sequence. The accuracy of diffusion models is assed in-vitro and the feasibility of high resolution
quantitative diffusion mapping is demonstrated in-vivo for human articular cartilage.
1632. Simultaneously Measuring Axonal Diameter Distribution and Direction of Rat Brain Using Q-Space
Diffusion Tensor Magnetic Resonance Imaging
Jun-Cheng Weng 1
1 Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan
Fundamental relationships between diffusion tensor imaging (DTI) and q-space imaging can be derived which establish conditions when these two
complementary MR methods are equivalent. When the 3D displacement distribution is measured by q-space imaging with large displacement and small q
vector, the result is similar to 3D Gaussian assumed in DTI. Combing displacement information from q-space imaging and fiber direction from DTI,
distribution of axonal diameters and directions could be derived at the same time. The study proposed a novel technique, q-space diffusion tensor imaging
(qDTI), combined with two image reconstruction methods based on the assumption to simultaneously map axonal diameter distribution and direction of rat
brain. One was tensor-based method. The 3D Gaussian displacement distribution could be obtained directly by the displacement tensor. The other was
displacement projection method. The effective axonal diameter was defined as the average of several displacements projected to the direction of the fiber
section. They provided MR images in which physical parameters of water diffusion such as the mean displacement and maximum diffusivity of water
molecules were used as image contrast. Our results demonstrated that two qDTI methods both produced reasonable distribution of effective axonal diameters
and directions in rat brain.