Application of Unsuppressed Water Peaks for MRS Thermometry

This study explores the feasibility of unsuppressed water (WU) peaks acquired as a part of prescanning in conjunction with metabolites from suppressed water (WS) spectra for temperature measurements. Calibrations and in vivo single-voxel 1H MRS was conducted on a 3-T GE scanner. Calibration constants for the water-chemical shift were obtained by using a temperature-controlled phantom containing an aqueous solution of N-acetyl aspartate (NAA), Creatine (Cr), and Choline (Cho). Estimations of absolute human brain temperature were performed utilizing the correlation of temperature to the water-chemical shift for the NAA, Cr, and Cho resonances. Commercially available single-voxel point-resolved spectroscopy (PRESS) sequences (repetition/echo time = 1500 ms/30 ms; voxel size 2 × 2 × 2 cm3) were used to acquire data for calibration of the metabolites’ chemical shift differences and in vivo temperature estimations. Each sequence included 16 averages without water suppression and 96 averages with water partially suppressed. In vivo study consisted of 2 PRESS sequences, one before and one after extensive 30-min fMRI task acquisition. The mean brain temperatures calculated using NAA, Cr, and Cho with WS were 37.49 ∓ 0.40 ℃, 37.09 ∓ 0.34 ℃, and 38.18 ∓ 0.37 ℃ before fMRI and 37.19 ∓ 0.45 ℃, 36.81 ∓ 0.39 ℃, and 37.88 ∓ 0.41 ℃ after fMRI, with a difference of approximately 0.3℃. When using WU with NAA, Cr, and Cho, the mean brain temperature was 38.13 ∓ 0.49 ℃, 37.67 ∓ 0.44℃, and 38.86 ∓ 0.52 ℃ before fMRI and 37.89 ∓ 0.52 ℃, 37.45 ∓ 0.50 ℃, and 38.62 ∓ 0.52℃ after fMRI, with a difference of approximately 0.24℃. Similar differences reported by using both methods for temperature calculation suggest that using unsuppressed water for temperature measurement in absence of its suppressed counterpart is feasible and may add another angle to already concluded past MRS studies which is temperature.