Optimization of magnetization-prepared 3-dimensional fluid attenuated inversion recovery imaging for lesion detection at 7 T.

Manojkumar Saranathan, Thomas Tourdias, Adam B. Kerr, Jeff D. Bernstein, Geoffrey A. Kerchner, May H. Han, Brian K. Rutt
Investigative Radiology. 2014-05-01; 49(5): 290-298
DOI: 10.1097/rli.0000000000000041

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1. Invest Radiol. 2014 May;49(5):290-8. doi: 10.1097/RLI.0000000000000041.

Optimization of magnetization-prepared 3-dimensional fluid attenuated inversion
recovery imaging for lesion detection at 7 T.

Saranathan M(1), Tourdias T, Kerr AB, Bernstein JD, Kerchner GA, Han MH, Rutt BK.

Author information:
(1)From the Departments of *Radiology, †Electrical Engineering, and ‡Neurology
and Neurological Sciences, Stanford University, Stanford, CA.

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 mm 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 mm isotropic resolution in short scan times and without
SAR penalty.

DOI: 10.1097/RLI.0000000000000041
PMCID: PMC4852716
PMID: 24566291 [Indexed for MEDLINE]

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