NONINVASIVE MEASUREMENTS OF HUMAN BRAIN TEMPERATURE USING VOLUME-LOCALIZED PROTON MAGNETIC-RESONANCE SPECTROSCOPY

Elucidation of the role of cerebral hyperthermia as a secondary factor that worsens outcome after brain injury, and the therapeutic applicat ion of modest brain hypothermia would benefit from noninvasive measure ments of absolute brain temperature. The present study was performed t o evaluate the feasibility of using H-1 magnetic resonance (MR) spectr oscopy to measure absolute brain temperature in human subjects on a cl inical imaging spectroscopy system operating at a field strength of 1. 5 T. In vivo calibration results were obtained from swine brain during whole-body heating and cooling, with concurrent measurements of brain temperature via implanted probes. Plots of the frequency differences between the in vivo MR peaks of water and N-acetyl-aspartate and relat ed compounds (NAX), or water and choline and other trimethylamines ver sus brain temperature were linear over the temperature range studied ( 28-40 degrees C). These relationships were used to estimate brain temp erature from H-1 MR spectra obtained from 10 adult human volunteers fr om 4 cm(3)-volumes selected from the frontal lobe and thalamus. Oral a nd forehead temperatures were monitored concurrently with MR data coll ection to verify normothermia in all the subjects studied. Temperature s determined using N-acetyl-aspartate or choline as the chemical shift reference did not differ significantly, and therefore results from th ese estimates were averaged. The brain temperature (mean +/- SD) measu red from the frontal lobe (37.2 = 0.6 degrees C) and thalamus (37.7 +/ - 0.6 degrees C) were significantly different from each other (paired t-test, p = 0.035). We conclude that H-1 MR spectroscopy provides a vi able noninvasive means of measuring regional brain temperatures in nor mal subjects and is a promising approach for measuring temperatures in brain-injured subjects.