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Signal‐to‐noise ratio and MR tissue parameters in human brain imaging at 3, 7, and 9.4 tesla using current receive coil arrays
Author(s) -
Pohmann Rolf,
Speck Oliver,
Scheffler Klaus
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25677
Subject(s) - homogeneity (statistics) , electromagnetic coil , flip angle , field strength , nuclear magnetic resonance , physics , signal to noise ratio (imaging) , magnetic field , computational physics , acoustics , magnetic resonance imaging , optics , mathematics , medicine , statistics , quantum mechanics , radiology
Purpose Relaxation times, transmit homogeneity, signal‐to‐noise ratio (SNR) and parallel imaging g‐factor were determined in the human brain at 3T, 7T, and 9.4T, using standard, tight‐fitting coil arrays. Methods The same human subjects were scanned at all three field strengths, using identical sequence parameters and similar 31‐ or 32‐channel receive coil arrays. The SNR of three‐dimensional (3D) gradient echo images was determined using a multiple replica approach and corrected with measured flip angle and T 2 * distributions and the T 1 of white matter to obtain the intrinsic SNR. The g‐factor maps were derived from 3D gradient echo images with several GRAPPA accelerations. Results As expected, T 1 values increased, T 2 * decreased and the B 1 ‐homogeneity deteriorated with increasing field. The SNR showed a distinctly supralinear increase with field strength by a factor of 3.10 ± 0.20 from 3T to 7T, and 1.76 ± 0.13 from 7T to 9.4T over the entire cerebrum. The g‐factors did not show the expected decrease, indicating a dominating role of coil design. Conclusion In standard experimental conditions, SNR increased supralinearly with field strength (SNR ∼ B 0 1.65 ). To take full advantage of this gain, the deteriorating B 1 ‐homogeneity and the decreasing T 2 * have to be overcome. Magn Reson Med 75:801–809, 2016. © 2015 Wiley Periodicals, Inc.