Evolution of brain temperature in ischemic tissues by ¹H magnetic resonance spectroscopy

Abstract

To explore the application of temperature measurement technique by ¹H magnetic resonance spectroscopy (MRS) in an ischemia monkey model. A MRI-compatible thermostatic control system was developed. And the equation was corrected between brain temperature and the chemical shift of N-acetyl-L-aspartic acid (NAA) through in vitro experiment. The normal brain temperature of monkey brain was measured. And a monkey model of middle cerebral artery occlusion (MCAO) and reperfusion was established. MR diffusion weighted imaging (DWI), perfusion weighted imaging (PWI), T2 weighted imaging and ¹H MRS were performed at artery occlusion stage, 1h, 3h, 6h, 12h and 24h post-recanalization. The brain temperatures of different ischemic regions were calculated by the modified brain temperature-chemical shift equation. The modified equation was as follows: T = 37+100 (CSNAA-2.039). The normal brain temperature was 37.16 °C. The models were successfully established in 4 monkeys. During arterial occlusion stage, the brain temperature of different ischemic tissue was higher than the contralateral hemisphere (P < 0.05), including infarct core, ischemic penumbra (IP) and oligemic region. And the highest temperature was in IP. After recanalization, the brain temperature of infarct core decreased rapidly during an early stage and was accompanied by a subsequent increase. However, the brain temperature of IP and oligemic region decreased slowly to normal. ¹H MRS may be used to measure brain temperature noninvasively so as to gauge ischemic degree.