Resting-State Brain Temperature: Dynamic Fluctuations in Brain Temperature and the Brain-Body Temperature Gradient.

Background: While fluctuations in healthy brain temperature have been investigated over time periods of weeks to months, dynamics over shorter time periods are less clear.
Purpose: To identify physiological fluctuations in brain temperature in healthy volunteers over time scales of approximately 1 hour.
Study Type: Prospective.
Subjects: A total of 30 healthy volunteers (15 female; 26 ± 4 years old).
Sequence and Field Strength: 3 T; T1-weighted magnetization-prepared rapid gradient-echo (MPRAGE) and semi-localized by adiabatic selective refocusing (sLASER) single-voxel spectroscopy.
Assessments: Brain temperature was calculated from the chemical shift difference between N-acetylaspartate and water. To evaluate within-scan repeatability of brain temperature and the brain-body temperature difference, 128 spectral transients were divided into two sets of 64-spectra. Between-scan repeatability was evaluated using two time periods, ~1-1.5 hours apart.
Statistical Tests: A hierarchical linear mixed model was used to calculate within-scan and between-scan correlations (R _w and R _b , respectively). Significance was determined at P ≤ .05. Values are reported as the mean ± standard deviation.
Results: A significant difference in brain temperature was observed between scans (-0.4 °C) but body temperature was stable (P = .59). Brain temperature (37.9 ± 0.7 °C) was higher than body temperature (36.5 ± 0.5 °C) for all but one subject. Within-scan correlation was high for brain temperature (R _w  = 0.95) and brain-body temperature differences (R _w  = 0.96). Between scans, variability was high for both brain temperature (R _b  = 0.30) and brain-body temperature differences (R _b  = 0.41).
Data Conclusion: Significant changes in brain temperature over time scales of ~1 hour were observed. High short-term repeatability suggests temperature changes appear to be due to physiology rather than measurement error.
Evidence Level: 2 TECHNICAL EFFICACY: Stage 1.
(© 2022 International Society for Magnetic Resonance in Medicine.)