Thomas Richard Barrick¹, Andrew Mott¹, Diggory North¹, and Franklyn Arron Howe^1
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.

Erpeng Dai¹, Xiaodong Ma¹, Zhe Zhang¹, Chun Yuan^1,2, and Hua Guo^1
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.

Kerstin Demberg¹, Frederik Bernd Laun¹, Johannes Windschuh¹, Reiner Umathum¹, Peter Bachert¹, and Tristan Anselm Kuder^1
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.

Eric Y. Pierre¹, Jacques-Donald Tournier^1,2, and Alan Connelly^1
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.

Eric Aliotta^1,2, Holden H Wu^1,2, and Daniel B Ennis^1,2
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.

Marco Lawrenz¹ and Juergen Finsterbusch^1
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.

Wenchuan Wu¹, Peter J Koopmans¹, Robert Frost¹, Myung-Ho In², Oliver Speck³, and Karla L Miller^1
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.

Jana Maria Hutter¹, J-Donald Tournier¹, Anthony N Price¹, Lucilio Cordero Grande¹, Emer Judith Hughes¹, Kelly Pegoretti¹, Laura McCabe¹, Mary Rutherford¹, and Joseph V Hajnal^1
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.

Matthew Budde¹ and Nathan Skinner^1
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.

Andreas Merrem¹, Jakob Klosowski¹, Sabine Hofer¹, Klaus-Dietmar Merboldt¹, and Jens Frahm^1
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.