Signal-to-noise ratio and MR tissue parameters in human brain imaging at 3, 7, and 9.4 tesla using current receive coil arrays

• Published in: Magnetic resonance in medicine Vol. 75; no. 2; pp. 801 - 809
• Main Authors: Pohmann, Rolf, Speck, Oliver, Scheffler, Klaus
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.02.2016; Wiley Subscription Services, Inc
• Subjects: Arrays; Brain; Brain Mapping - methods; Cerebrum; Design standards; Field strength; Homogeneity; Humans; Image Enhancement - methods; Image Processing, Computer-Assisted - methods; Imaging, Three-Dimensional; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Male; Neuroimaging; Parameters; Phantoms, Imaging; relaxation times; Signal-To-Noise Ratio; Substantia alba; ultra-high field; ultra-high field; relaxation times; signal-to-noise ratio
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.25677

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 T2* distributions and the T1 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, T1 values increased, T2* decreased and the B1‐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 ∼ B01.65). To take full advantage of this gain, the deteriorating B1‐homogeneity and the decreasing T2* have to be overcome. Magn Reson Med 75:801–809, 2016. © 2015 Wiley Periodicals, Inc.