Variable Density Compressed Sensing Single Shot Fast Spin Echo

Valentina Taviani^{1}, Daniel V. Litwiller^{2}, Jonathan I. Tamir^{3}, Andreas M. Loening^{1}, Brian A. Hargreaves^{1}, and Shreyas S. Vasanawala^{1}

[1] Loening AM, Saranathan M, Ruangwattanapaisarn N, Litwiller DV, Shimakawa A, Vasanawala SS. Increased speed and image quality in single-shot fast spin echo imaging via variable refocusing flip angles. J Magn Reson Imaging 2015; Epub ahead of print.

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[3] Uecker M, Ong F, Tamir JI, Bahri D, Virtue P, Cheng JY, Zhang T, Lustig M. Berkeley Advanced Reconstruction Toolbox. Proc. Intl. Soc. Mag. Reson. Med. 2015; 23:2486.

[4] Brau AC, Beatty PJ, Skare S, Bammer R. Comparison of reconstruction accuracy and efficiency among autocalibrating data-driven parallel imaging methods. Magn Reson Med 2008; 59:382-95.

Regular, VD and asymmetric
VD sampling (A). Note incoherent aliasing introduced by the VD pseudo-random sampling
pattern (B). In principle, VD can sample the VRF-generated signal more
efficiently, especially when low minimum refocusing flip angles are used, resulting
in almost constant signal levels towards the center of k-space (C).

VD CS SSFSE gives less
residual aliasing and noise amplification than regular undersampling, effectively
allowing higher acceleration factors and up to 25% shorter echo times.

Regular undersampling with ARC (A) and VD CS SSFSE (B) give similar
image quality and nearly identical TE (143ms) and TR (592/597ms) for the same
number of phase-encoding (R=2.5) and autocalibrating (N=20) lines. Other
imaging parameters common to both acquisitions were: 40cm FOV, 320×224 matrix, 5mm slice thickness, 83.3kHz bandwidth.

2.5x regular undersampling (A) vs. 3.3x VD CS SSFSE (B). Shorter TEs and
TRs were obtained with VD CS SSFSE. Note improved visualization of liver
parenchyma at shorter echo times (same window level between A and B). In all
cases, a 320×224 matrix, 5mm slice thickness and 83.3kHz bandwidth were used. FOV
ranged between 30 and 48cm.

(A) 320×224 matrix with 2.5x regular sampling vs. (B) 320×320 matrix with 2.5x asymmetric VD sampling (40cm
FOV, 5mm slice thickness, 83.3kHz bandwidth). Asymmetric VD allowed higher
resolution (30% smaller voxels) while preserving image quality. Note increased
sharpness of liver capsule (yellow arrows) and pancreatic duct (white arrows).

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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