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Optimization of Magnetization-Prepared 3-Dimensional Fluid Attenuated Inversion Recovery Imaging for Lesion Detection at 7 T

Saranathan, Manojkumar PhD*; Tourdias, Thomas MD, PhD*; Kerr, Adam B. PhD; Bernstein, Jeff D. BS; Kerchner, Geoffrey A. MD, PhD; Han, May H. MD; Rutt, Brian K. PhD*

doi: 10.1097/RLI.0000000000000041
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Purpose The aim of this study was to optimize the 3-dimensional (3D) fluid attenuated inversion recovery (FLAIR) pulse sequence for isotropic high-spatial-resolution imaging of white matter (WM) and cortical lesions at 7 T.

Materials and Methods We added a magnetization-prepared (MP) FLAIR module to a Cube 3D fast spin echo sequence and optimized the refocusing flip angle train using extended phase graph simulations, taking into account image contrast, specific absorption rate (SAR), and signal-to-noise ratio (SNR) as well as T1/T2 values of the different species of interest (WM, grey matter, lesions) at 7 T. We also effected improved preparation homogeneity at 7 T by redesigning the refocusing pulse used in the MP segments. Two sets of refocusing flip angle trains—(a) an SNR-optimal and (b) a contrast-optimal set—were derived and used to scan 7 patients with Alzheimer disease/cognitive impairment and 7 patients with multiple sclerosis. Conventional constant refocusing flip MP-FLAIR images were also acquired for comparison. Lesion SNR, contrast, and lesion count were compared between the 2 optimized and the standard FLAIR sequences.

Results Whole brain coverage with 0.8 mm3 isotropic spatial resolution in ∼5-minute scan times was achieved using the optimized 3D FLAIR sequences at clinically acceptable SAR levels. The SNR efficiency of the SNR-optimal sequence was significantly better than that of conventional constant refocusing flip MP-FLAIR sequence, whereas the scan time was reduced more than 2-fold (∼5 vs >10 minutes). The contrast efficiency of the contrast-optimal sequence was comparable with that of the constant refocusing flip sequence. Lesion load ascertained by lesion counting was not significantly different among the sequences.

Conclusion Magnetization-prepared FLAIR-Cube with refocusing flip angle trains optimized for SNR and contrast can be used to characterize WM and cortical lesions at 7 T with 0.8 mm3 isotropic resolution in short scan times and without SAR penalty.

Supplemental Digital Content is available in the article.

From the Departments of *Radiology, †Electrical Engineering, and ‡Neurology and Neurological Sciences, Stanford University, Stanford, CA.

Received for publication July 19, 2013; and accepted for publication, after revision, December 18, 2013.

Conflicts of interest and sources of support: This work was supported by NIH/NCRR P41, EB015891-19, and General Electric Healthcare. One of the authors (TT) received financial support from ARSEP Foundation (Fondation pour l’aide à la recherche sur la Sclérose en Plaques), CHU de Bordeaux, Fondation Université de Bordeaux, the TRAIL program-France, Institut Servier, and France-Stanford Center for Interdisciplinary studies.

Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.investigativeradiology.com).

Reprints: Manojkumar Saranathan, PhD, Department of Radiology, Lucas Center, MC 5488, Stanford University, Stanford CA 94305. E-mail: manojsar@stanford.edu.

© 2014 by Lippincott Williams & Wilkins