Reliability of MRSI brain temperature mapping at 1.5 and 3 T

MRSI permits the non-invasive mapping of brain temperature in vivo, but information regarding its reliability is lacking. We obtained MRSI data from 31 healthy male volunteers [age range, 22-40 years; mean +/- standard deviation (SD), 30.5 +/- 5.0 years]. Eleven subjects (age range, 23-40 years; mean +/- SD, 30.5 +/- 5.2 years) were invited to receive four point-resolved spectroscopy MRSI scans on each of 3 days in both 1.5-T (TR/TE=1000/144 ms) and 3-T (TR/TE=1700/144 ms) clinical scanners; a further 20 subjects (age range, 22-40 years; mean +/- SD, 30.5 +/- 4.9 years) were scanned on a single occasion at 3 T. Data were fitted in the time domain to determine the water-N-acetylaspartate chemical shift difference, from which the temperature was estimated. Temperature data were analysed using a linear mixed effects model to determine variance components and systematic temperature changes during the scanning sessions. To characterise the effects of instrumental drift on apparent MRSI brain temperature, a temperature-controlled phantom was constructed and scanned on multiple occasions. Components of apparent in vivo temperature variability at 1.5 T/3 T caused by inter-subject (0.18/0.17 degrees C), inter-session (0.18/0.15 degrees C) and within-session (0.36/0.14 degrees C) effects, as well as voxel-to-voxel variation (0.59/0.54 degrees C), were determined. There was a brain cooling effect during in vivo MRSI of 0.10 degrees C [95% confidence interval (CI): -0.110, -0.094 degrees C; p