Regional neonatal brain absolute thermometry by 1H MRS.

Therapeutic hypothermia is standard care for infants with moderate to severe encephalopathy. 1H MRS thermometry (MRSt) measures regional brain absolute temperature using the temperature-dependent water chemical shift. This study evaluates the clinical feasibility of MRSt in human neonates, and correlates white matter (WM) and thalamus (Thal) MRSt with conventional rectal temperature (Trectal) measurement. Fifty-six infants born at term underwent perinatal MRSt for suspected hypoxicischaemic brain injury and 33 infants born preterm had MRSt at a term-equivalent age; 56 of the 89 had Trectal measured after MRSt of either a Thal or posterior WM voxel, or both. MRSt used point-resolved spectroscopy (no water suppression; TR=1370ms; TE=288ms; 1.5x1.5x1.5cm3 Thal and 1.1x1.3x1.4cm3 WM voxels). Time domain data were phase and frequency corrected before summation and motion-corrupted data were excluded from further analysis using simple criteria [preprocessing+quality assurance (QA)]. Two published water temperature-dependence calibrations [both using cerebral creatine (Cr), choline (Cho) and N-acetylaspartate (Naa) as independent reference peaks] were compared. The temperature measurements derived from Cr, Cho and Naa were combined to give a single amplitude-weighted combination temperature (TAWC). WM and Thal TAWC correlated linearly with Trectal (Thal slope, 0.82 +/- 0.04, R2=0.85, p<0.05; WM slope, 0.95 +/- 0.04, R2=0.78, p<0.05). Preprocessing+QA improved the correlation between WM TAWC and Trectal (R2 increased from 0.27 to 0.78, p<0.001). Both calibration datasets showed specific inconsistencies between the temperatures calculated using Cr, Cho and Naa reference peaks when applied to this neonatal dataset. Neonatal MRSt is clinically feasible. Preprocessing+QA improved MRSt reliability in WM. The consideration of MRSt calibration internal biases is necessary before combining MRSt temperatures from multiple reference peaks to obtain TAWC. Copyright (c) 2012 John Wiley & Sons, Ltd.