ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Scientific Session: Diffusion Acquisition

Monday, May 9, 2016
Room 324-326
16:30 - 18:30
Moderator: Kawin Setsompop

Optimal data acquisition for application to the continuous time random walk diffusion model - Permission Withheld
Thomas Richard Barrick1, Andrew Mott1, Diggory North1, and Franklyn Arron Howe1
1Neuroscience Research Centre, St George's, University of London, London, United Kingdom
This study aims to optimise diffusion-weighted MRI (DW-MRI) acquisition for applications involving the continuous time random walk (CTRW) diffusion model. Minimum acquisition time and effects of inversion recovery are considered.  Optimisation indicates a 6 minute 4 b-value DW-MRI acquisition is sufficient for diffusion tensor data. Inversion recovery significantly reduces the variability in calculated α, β and ADC due to effects of CSF in grey matter and periventricular white matter. Analysis of water diffusion in brain with the CTRW model may reveal more subtle effects of neuronal damage than conventional DWI.

The Effects of Navigator Distortion Level on Interleaved EPI DWI Reconstruction: A Comparison between Image and K-space Based Method
Erpeng Dai1, Xiaodong Ma1, Zhe Zhang1, Chun Yuan1,2, and Hua Guo1
1Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, 2Vascular Imaging Laboratory, Department of Radiology, University of Washington, Seattle, WA, United States
One of the challenges for interleaved EPI (iEPI) DWI is the phase inconsistency among different shots. Several methods, performed either in the image or k-space domain, have been proposed to solve this problem with extra acquired navigator data. However, the navigator is usually acquired with a lower bandwidth in the phase encoding direction than the image echo, which can cause different distortion levels. In this study, the effects of such distortion for the image or k-space based reconstruction are investigated. It has been shown that the k-space based method is more tolerant to the navigator distortion.

Experimental detection of imaginary signals in diffusion pore imaging using double diffusion encoding - Permission Withheld
Kerstin Demberg1, Frederik Bernd Laun1, Johannes Windschuh1, Reiner Umathum1, Peter Bachert1, and Tristan Anselm Kuder1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
By diffusion pore imaging, the average shape of arbitrary closed pores in an imaging volume element can be detected employing a long-narrow gradient profile. Alternative approaches use short gradient pulses only. Until now, however, diffusion pore imaging of non-point-symmetrically shaped pores has not been demonstrated using short gradient pulses only. In this abstract, we present a first experimental verification using double diffusion encoded experiments. Non-point-symmetric pores result in non-vanishing imaginary parts in the double diffusion encoded signal. Thus the phase of the form factor can be estimated with an iterative approach. This allows for unambiguous pore image reconstruction.

Virtual Coil Reconstruction for 3D Diffusion-Weighted Multi-Shot MRI using a Single Reference Shot.
Eric Y. Pierre1, Jacques-Donald Tournier1,2, and Alan Connelly1
1Florey Institute of Neuroscience and Mental Health, Melbourne, Australia, 2Centre for the Developing Brain, King's College London, London, United Kingdom
We introduce an efficient Mult-Shot Diffusion-Weighted (DW) 3D-GRASE acquisition and reconstruction technique to produce DW image volumes free of motion-induced phase artifacts, without relying on explicit measurement or inference of the phase information. The method replaces navigators measurements by a single reference scan for the whole acquisition. Virtual Coil concepts for Parallel Imaging techniques are used to map the multi-shot data onto a k-space signal with consistent phase information.

Convex Optimized Diffusion Encoding (CODE) Gradient Waveforms for Minimum TE and Bulk Motion Compensated Diffusion Weighted MRI
Eric Aliotta1,2, Holden H Wu1,2, and Daniel B Ennis1,2
1Radiological Sciences, UCLA, Los Angeles, CA, United States, 2Biomedical Physics IDP, UCLA, Los Angeles, CA, United States
Spin-Echo EPI Diffusion Weighted MRI (SE-EPI DWI) typically uses a  diffusion encoding gradient waveform with two identical gradients on either side of the 180° pulse which, in combination with the temporal footprint of the EPI readout results in sequence dead time. This dead time can be used for additional diffusion encoding which can, in turn, reduce TE and/or be used to null gradient moments for bulk motion compensated diffusion encoding. Convex Optimized Diffusion Encoding (CODE) was developed to minimize TE for DWI with and without motion compensation, implemented on a clinical scanner and tested in volunteers.

Detection of Microscopic Diffusion Anisotropy in Human Brain Cortical Gray Matter in Vivo with Double Diffusion Encoding
Marco Lawrenz1 and Juergen Finsterbusch1
1Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
Double diffusion encoding experiments with two weighting periods applied successively in the same acquisition offer access to microscopic tissue properties. Rotationally invariant measures of the so-called microscopic diffusion anisotropy as a marker for cell or compartment shape have reliably been determined in brain white matter. In this study, it is demonstrated that microscopic diffusion anisotropy can also be detected in cortical gray matter in vivo and measures of it can be determined extending first evidences presented recently. However, an inversion recovery pulse is required to null white matter signals and avoid partial volume effects.

High-resolution diffusion imaging at 7T using 3D multi-slab EPI
Wenchuan Wu1, Peter J Koopmans1, Robert Frost1, Myung-Ho In2, Oliver Speck3, and Karla L Miller1
1FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, 2Department of Neurologic Surgery, Mayo Clinic, Rochester, MN, United States, 3Department of Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany
In this work, we combined 3D multi-slab imaging (optimal SNR efficiency for spin-echo sequence) and 7T (higher SNR) to enhance diffusion imaging. With the newly developed Slice-FLEET technique and NPEN correction, we successfully achieved robust high resolution diffusion MRI at 7T with high SNR.

Efficient quiet multiband accelerated HARDI fetal Diffusion
Jana Maria Hutter1, J-Donald Tournier1, Anthony N Price1, Lucilio Cordero Grande1, Emer Judith Hughes1, Kelly Pegoretti1, Laura McCabe1, Mary Rutherford1, and Joseph V Hajnal1
1Centre for the developing brain, King's College London, London, United Kingdom
 Fetal diffusion MRI analysis is often limited by the ability of the conventional ssEPI to allow an efficient, high-resolution acquisition, able to produce multi-shell high angular resolution dMRI data as required by advanced analysis tools. This abstract presents a novel, multiband accelerated, sinusoidal, quiet and efficient ssEPI acquisition. The first results on 3 fetuses with 54 directions show promising data quality and significantly decreased scan time.

Microscopic Anisotropy of the Rat Spinal Cord In vivo with DW PRESS
Matthew Budde1 and Nathan Skinner1
1Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States
Diffusion weighted imaging of the spinal cord has seen promising applications to diagnosis and prognosis, yet it is limited by technical challenges.  This work presents the implementation of diffusion weighted spectroscopy of the water signal in the rat spinal cord in vivo with the goal of reducing acquisition times and post processing requirements to promote wider clinical feasibility.

Diffusion-weighted MRI using undersampled radial STEAM with iterative image reconstruction
Andreas Merrem1, Jakob Klosowski1, Sabine Hofer1, Klaus-Dietmar Merboldt1, and Jens Frahm1
1Biomedizinische NMR Forschungs GmbH, Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany
Single-shot STEAM MRI is a method for black-blood diffusion-weighted imaging where the use of radiofrequency-refocussed echoes leads to no image distortions, no susceptibility artifacts, and no violations of the Carr-Purcell-Meiboom-Gill condition. Despite these favorable properties, clinical applications have been limited by a low signal-to-noise ratio. Here, we demonstrate the development of highly undersampled radial diffusion-weighted single-shot STEAM MRI with iterative reconstruction to achieve acceptable signal-to-noise for studies of the human brain.

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