Lipeng Ning1,2, Kawin Setsompop2,3, and Yogesh Rathi1,2
1Brigham and Women's Hospital, Boston, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Massachusetts General Hospital, Boston, MA, United States
Synopsis
We introduce a new method for rapid acquisition of sub-millimeter whole-brain
diffusion imaging. Our method combines the gSlider-SMS acquisition method and
the compressed-sensing super-resolution reconstruction algorithm. We
demonstrate that this proposed approach is able to increase the resolution to 860μm iso in an effective
acquisition time of 12 min.Purpose
Submillimeter isotropic diffusion imaging (DI) is made difficult by long
acquisition time and low SNR. Slider-SMS acquisition
1 has recently
been proposed to provide large improvement to SNR efficiency for DI, by
allowing a large number of imaging slices to be acquire simultaneously through
the combined use of SMS parallel imaging and super-resolution approaches. Further
improvement to this acquisition with a new generalized Slider approach
(gSlider) is also being proposed
2, which utilizes RF encoding to
improve the orthogonality of the slice-encoding basis for super-resolution, to
enable high quality 5 simultaneous slice super-resolution, which when combines
with SMS parallel imaging can achieve highly efficient 10 simultaneous slices
DI (gSlider x MB = 5x2). In this work,
we provide further improvement to this acquisition by incorporating the
framework of Compressed Sensing for
Super-Resolution Diffusion (CS-RSD) proposed in
3 to gSlider-SMS. This
enables acquisition acceleration through under-sampling of the gSlider
slice-encoded super-resolution acquisitions needed for super-resolution
reconstruction of each diffusion direction (with different random undersampling
for different diffusion directions). Such acquisition undersampling is made
possible through sparsity enforce reconstruction where the diffusion
signal in each voxel of the final high-resolution image is enforced to be sparse
in the basis of spherical ridgelets. We demonstrate that the incorporation of
the CS-RSD approach enables a further 2x efficiency gain to an already highly
efficient 10 simultaneous slice gSlider-SMS acquisition. This permits, for the
first time, high quality 860μm whole-brain DI at high b-value to be perform in
a relevant clinical timeframe of 8 minutes.
Method
gSlider-SMS data with 10 simultaneous slice
acquisition (gSlider×MB = 5×2) were acquired in a healthy volunteer on the 3T
CONNECTOM system using custom-built 64-channel
array. Imaging parameters were: 860μm iso; FOV 220×163.4×130 mm
3;
p.f. 6/8; TE = 64ms and TR per
thick-slice volume = 4.2s; effective echo spacing = 0.32ms, 64 directions at
b=2000 s/mm
2 with interspersed b0 every 10 volumes, where for each diffusion
direction, imaging were performed 5 times for different RF gSlider encoding,
total scan-time ~25 min. Background phase removal was performed using real
value diffusion algorithm
4. Reconstruction for full sampled Slider encoding
data were performed using Tikhonov regularized super-resolution reconstruction
to represent fully-sampled acquisition for comparison. For incorporation of
CS-RSD, the 5 different gSlider slice-encode imaging per diffusion direction
were randomly undersampled to provide 2x acceleration to result in an effective
acquisition time of ~12 min. This accelerated acquisition is reconstructed
using algorithm proposed in3 and compared with the fully sampled
reconstruction.
Results
Figure (1) shows the acquired thick-slice images and the reconstructed
high-resolution diffusion-weighted images obtained using the Tikhonov
regularization and the compressed-sensing approach, respectively. The
high-resolution image obtained using the compressed-sensing approach has the
lowest noise level due to the sparse representation using spherical ridgelets.
Figure (2) shows the glyph results in a cortical gray-matter region of the
three diffusion MRI volumes, respectively, with color-coded by the principle direction
of the underlying diffusion tensors. The glyphs obtained using the
compressed-sensing method have a similar pattern as in the result given by the
Tikhonov regularization.
Acknowledgements
The authors would like to acknowledge the following grants from the National Institutes of Health which supported this work: R01MH099797 (PI: Rathi), R00EB012107 (PI: Setsompop).References
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