VALIDATION OF A NONINVASIVE METHOD TO MEASURE BRAIN TEMPERATURE IN-VIVO USING H-1-NMR SPECTROSCOPY

The goal of this study was to evaluate the potential of using the diff erence between the H-1 NMR frequencies of water and N-acetylaspartic a cid (NAA) to measure brain temperature noninvasively. All water-suppre ssed and non-water-suppressed H-1 NMR spectra were obtained at a field strength of 4.7 T using a surface coil. Experiments performed on mode l solutions revealed a decrease in the difference between NMR frequenc ies for NAA and water as a linear function of increasing temperature f rom 14 to 45 degrees C. Changing pH in the range 5.5-7.6 produced no d iscernible trends for concurrent changes in the slope and intercept of the linear relationship. There were minor changes in slope and interc ept for solutions containing 80 or 100 mg of protein/ml versus no prot ein, but these changes were not considered to be of sufficient magnitu de to deter the use of this approach to measure brain temperature. The protein content of swine cerebral cortex was found to remain constant from newborn to 1 month old (78 +/- 12 mg/g; n = 41). Therefore, data collected for the model solution containing 80 mg of protein/ml were used as a calibration curve to calculate brain temperature in eight sw ine during control, hypothermia, ischemia, postischemia, or death, ove r a temperature range of 23-40 degrees C. A plot of 61 temperatures de termined from H-1 NMR versus temperatures measured from an optical fib er probe sensor implanted 1 cm into the cerebral cortex showed excelle nt linear agreement (slope = 1.00 +/- 0.03, r(2) = 0.96). We conclude that H-1 NMR spectroscopy presents a practical means of making noninva sive measurements of brain temperature with an accuracy of better than +/-1 degrees C.