Kim Annink

222 Chapter 10 was expected at ~ 2.02 ppm. As selective excitation was used for water suppression, the residual water peak is still in phase and can be used to determine its frequency position. The positions of the NAA and H 2 O peak in the spectrum were determined automatically by using the ‘HLSVDPro’-option of the jMRUI software, which determines the spectral position of the fifteen highest peaks automatically (17). Figure 1: Example of long TE 1 H-MRS showing the ΔH 2 O-NAA and determination of the quality of the spectrum including visual estimation signal to noise ratio of NAA peak (signal NAA is more than 3 times the noise) and determination of the band width (lower than 10Hz). Peak 1 is the H 2 O peak, peak 2 is the choline peak and peak 3 is the NAA peak. Statistical tests Statistical analysis was performed using IBM SPSS Statistics for Windows version 25.0 (IBM Corp., Illinois, USA). Linear univariate regression analysis was performed, with the actual temperature of the water bath as independent variable and ΔH 2 O- NAA as dependent variable, to develop the new, calibrated formula to calculate brain temperature for validation. Paired sample t-tests for normally distributed and Wilcoxon Signed rank tests for non-Gaussian distributions were performed to compare the brain temperatures calculated with the two formulas and with short versus long TEs. The Pearson correlation for normally distributed parameters and Spearman correlation for non-Gaussian distributed parameters were used to test the association between brain temperatures and rectal temperatures. The Kruskal-Wallis-H test was performed to calculate differences amongst temperature