Reliability of MRSI brain temperature mapping at 1.5 and 3 T

MRSI permits the non-invasivemapping 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 °C), inter-session (0.18/0.15 °C) and within-session (0.36/0.14 °C) effects, as well as voxel-to-voxel variation (0.59/0.54 °C), were determined. There was a brain cooling effect during in vivo MRSI of 0.10 °C [95 % confidence interval (CI): –0.110, –0.094 °C; p< 0.001] and 0.051 °C (95 % CI: –0.054, –0.048 °C; p<0.001) per scan at 1.5 T and 3 T, respectively, whereas phantom measurements revealed minimal drift in apparent MRSI temperature relative to fibre-optic temperature measurements. The mean brain temperature at 3 T was weakly associated with aura