INTRODUCTION: Magnetic resonance spectroscopy (MRS) thermometry is an innovative method for non-invasive, localized brain temperature measurement, but its stability across repeated visits remains insufficiently researched.

AIM(S): In this study, we aimed to assess the stability of MRS thermometry by testing whether temperature changes after prolonged fMRI are reproducible across two visits.

METHOD(S): In vivo data from forty-three healthy adults (22F, 21M) were acquired across two visits (median interval: 200 days). At each visit, two 1HMRS PRESS spectra were acquired from each subject: one before and after 30-minute fMRI session. Temperature was estimated using previously acquired calibration data sets and water-metabolite chemical shift differences between suppresed (WS) and unsupressed (WU) water and N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) used as references.

RESULTS: Across all methods and both visits, temperature change was consistently negative, indicating post-fMRI cooling. Measured mean cooling was approximately -0.25°C for WS (NAA/Cr/Cho; all p < 0.001) and -0.16°C for WU (NAA/Cr/Cho; all p < 0.001). Cooling occurred in ~80% of WS and ~65% of WU observations. Absolute temperature measurements showed systematic offset with WU yielding higher values by ~0.6°C. Sensitivity analyses confirmed the direction and significance of cooling.

CONCLUSIONS: Prolonged fMRI is associated with small but robust decrease in brain temperature across all used methods. WS provides higher stability and larger apparent cooling, while absolute temperature measurements depend on acquisition type. We believe that using MRS thermetry for longitudinal studies is feasible.

FINANCIAL SUPPORT: This study was part of the grant NCBR nr POIR.01.01.01-00-0178/15-00