Water proton T (1) measurements in brain tissue at 7, 3, and 1.5T using IR-EPI, IR-TSE, and MPRAGE: results and optimization

• Published in: Magma (New York, N.Y.) N.Y.), 2008-03, Vol.21 (1-2), p.121-130
• Main Authors: Wright, P J, Mougin, O E, Totman, J J, Peters, A M, Brookes, M J, Coxon, R, Morris, P E, Clemence, M, Francis, S T, Bowtell, R W, Gowland, P A
• Format: Article
• Language: English
• ISSN: 0968-5243
• DOI: 10.1007/s10334-008-0104-8

Method: This paper presents methods of measuring the longitudinal relaxation time using inversion recovery turbo spin echo (IR-TSE) and magnetization-prepared rapid gradient echo (MPRAGE) sequences, comparing and optimizing these sequences, reporting T (1) values for water protons measured from brain tissue at 1.5, 3, and 7T. T (1) was measured in cortical grey matter and white matter using the IR-TSE, MPRAGE, and inversion recovery echo planar imaging (IR-EPI) pulse sequences. Results: In four subjects the T (1) of white and grey matter were found to be 646c32 and 1,197c134ms at 1.5T, 838c50 and 1,607c112ms at 3T, and 1,126c97, and 1,939c149ms at 7T with the MPRAGE sequence. The T (1) of the putamen was found to be 1,084c63ms at 1.5T, 1,332c68ms at 3T, and 1,644c167ms at 7T. The T (1) of the caudate head was found to be 1,109c 66ms at 1.5T, 1,395c49ms at 3T, and 1,684c76ms at 7T. Discussion: There was a trend for the IR-TSE sequence to underestimate T (1) in vivo. The sequence parameters for the IR-TSE and MPRAGE sequences were also optimized in terms of the signal-to-noise ratio (SNR) in the fitted T (1). The optimal sequence for IR-TSE in terms of SNR in the fitted T (1) was found to have five readouts at TIs of 120, 260, 563, 1,221, 2,647, 5,736ms and TR of 7 s. The optimal pulse sequence for MPRAGE with readout flip angle =8' was found to have five readouts at TIs of 160, 398, 988, 2,455, and 6,102ms and a TR of 9 s. Further optimization including the readout flip angle suggests that the flip angle should be increased, beyond levels that are acceptable in terms of power deposition and point-spread function.