Traditional Posters: Diffusion & Perfusion - ismrm

1620. Improved 3-Dimensional Reconstruction of Diffusion Data Using Overlapping Slices
Rita G. Nunes 1 , Joseph V. Hajnal 1
1 Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith
Hospital, Imperial College London, London, United Kingdom
As Diffusion-Weighted images are inherently very sensitive to motion, full brain coverage is achieved by imaging multiple 2D single
shot slices. However, as most fiber tracts in the brain have a 3-dimensional structure, ensuring that the anatomy is fully sampled along
all three dimensions is likely to be important. Conventionally, the same slice prescription is used for all diffusion sensitization
directions. We demonstrate that by using overlapping slices and/or combining slices acquired along orthogonal directions higher
fidelity anisotropy maps can be reconstructed. Using this type of geometry should also increase data robustness in the presence of
more severe subject motion.
1621. Diffusion Weighted Turbo-STEAM ZOOM Imaging of the Lumbar Spine
Patrick Hiepe 1 , Karl-Heinz Herrmann 2 , Christian Ros 2 , Jürgen R. Reichenbach 2
1 Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena University Hospital ,
Jena, Germany; 2 Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena
University Hospital, Jena, Germany
So far, most clinical DWI applications have relied on EPI although DWI EPI is limited by susceptibility artifacts. STEAM MRI with
robust turbo-FLASH readout is a fast imaging technique with subsecond measurement times. This robustness is traded against SNR by
using a less signal efficient acquisition technique. To achieve maximum efficiency of the turbo-STEAM sequences a reduced number
of PE lines is necessary. An effective way is to utilize the ZOOM imaging technique, which limits the excited FOV in the PE direction
to include only the ROI. This can be used to measure various regions of the body with a narrow FOV, e.g. lumbar spine, without the
occurrence of foldover or aliasing artifacts. In comparison with EPI, DW ZOOM single-shot STEAM MRI of the lumbar spine
exhibits a reduced SNR, but avoids regional signal losses and geometric distortions. Furthermore, no fat suppression is necessary. Our
case report indicates that the DW ZOOM turbo-STEAM MRI technique appears to be a good alternative to the standard DW EPI.
1622. Parallel Line Scan Diffusion Tensor Imaging
Renxin Chu 1 , Bruno Madore 1 , Lawrence P. Panych 1 , Stephan E. Marier 1
1 Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States
Diffusion tensor imaging (DTI) has been widely used in the study of white matter-related diseases. Single-shot echo-planar imaging
(EPI) is usually the preferred technique, but EPI images may exhibit severe geometric distortions, especially near the skull base. Line
scan diffusion imaging (LSDI) is a one-dimensional Fourier encoding technique with considerable robustness against motion and
geometric distortions. We present a parallel LSDI diffusion tensor imaging technique with acceleration along two dimensions, with
3D whole brain coverage and four-fold acceleration. The speed-up remarkably comes at no cost in SNR, and preserves the LSDI
immunity to susceptibility-induced signal losses and geometric image distortions.
1623. SIR-EPI Diffusion Imaging for 3-Fold Faster Scan Time to Enable Trade-Offs in
Slice Coverage and Gradient Duty Cycle Reduction.
Sudhir Ramanna 1 , Vibhas Deshpande 2 , David Feinberg 1,3
1 Advanced MRI Technologies, Sebastopol, CA, United States; 2 Siemens, United States; 3 University of
California, Berkeley, San Francisco, CA, United States
The use of high b-values encoded with lengthy high amplitude gradient pulses place limitations on diffusion imaging with HARDI
techniques. In this work, we develop and evaluate SIR with two and three echoes per read period (SIR-2, SIR-3) for HARDI imaging.
Both SIR-2 and SIR-3 EPI sequences are shown to be useful for simply reducing scan time, for obtaining higher resolution or field of
view on the slice axis with more slices per TR or instead controlling the heat limitations using high b-values by reducing the gradient
duty cycle in HARDI acquisitions.
Diffusion: Distortion Correction, QA & Miscellaneous
Hall B Wednesday 13:30-15:30
1624. Performance of Single Spin-Echo and Doubly-Refocused Diffusion-Weighted
Sequences in the Presence of Eddy Current Fields with Multiple Components Compared
Using Affine Registration
Rita G. Nunes 1 , Ivana Drobnjak 2 , Stuart Clare 3 , Peter Jezzard 3 , Mark Jenkinson 3
1 Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith
Hospital, Imperial College London, London, United Kingdom; 2 Centre for Medical Image Computing,
University College London, London, United Kingdom; 3 Oxford Centre for Functional Magnetic Resonance
Imaging of the Brain, University of Oxford, Oxford, United Kingdom
Echo-planar diffusion-weighted images can display significant geometric distortions due to eddy current fields. Several diffusion
preparation schemes have been proposed, which can null eddy currents with a single time constant. We use an MRI simulator to
compare the performance of three such sequences in the presence of multiple components, and investigate whether affine registration
is capable of correcting for the resulting distortions. Our study confirms that, in general, doubly-refocused sequences perform better
than single spin-echo approaches, and suggest that when the use of two refocusing pulses is not desirable, it may be preferable to use a
modified single spin-echo sequence.