MR relaxation times in human brain: Measurement at 4 T

PURPOSE: To determine the values for relaxation times in human brain for magnetic resonance (MR) imaging at 4 T. MATERIALS AND METHODS: T1 measurements were made with a progressive saturation sequence, an implementation of the Look-Locker sequence, and an inversion-recovery (IR) interleaved echo-planar imaging (IEPI) sequence. T2 measurements were made with a standard spin-echo (SE) sequence and an SE IEPI sequence. RESULTS: The T1 measurements yielded values of 1,724 msec +/- 51 for gray matter, 1,043 msec +/- 27 for white matter, and 4,550 msec +/- 800 msec for cerebrospinal fluid. The deep gray matter regions had T1 values of 1,458 +/- 38 (caudate nucleus) and 1,372 +/- 60 (putamen). The T2 measurements yielded results of 63 msec +/- 6.2 for gray matter and 49.8 msec +/- 2.2 for white matter. CONCLUSION: The T1 values measured at 4 T show a higher value than predicted from extrapolation at lower field strengths. The T2 measurements showed a slight decrease in values over those measured at lower field strength. The gain in signal-to-noise ratio from the higher field strength may be substantially offset by these altered relaxation time values to a degree that is sequence dependent.