Kim Annink

228 Chapter 10 DISCUSSION This study showed that it is feasible to estimate brain temperature using 1 H-MRS in infants with NE with the formula of Wu et al. and with as well short as long TE 1 H-MRS in magnets with field strengths of 1.5T or 3.0T. Secondly, brain temperature remained within physiological range and was not higher, but even lower in some infants during MRI compared to rectal temperature at the NICU. Different methods to determine brain temperature were compared to assess the feasibility in clinical practice. A previously developed formula of Wu et al. (8) was compared to a new formula developed based on temperature calibration for the 3.0T MR scanner used in our institute for neonatal MRI. A significant difference between brain temperatures calculated with the two formulas would have implied that calibration is essential. Nonetheless, brain temperatures measured with these two different formulas did not differ for short TE 1 H-MRS (mean difference 0.06˚C) and the difference for long TE 1 H-MRS was statistically borderline significant. However, the mean difference between the formulas for long TE 1 H-MRS was 0.15˚C, which is clinically insignificant. Verius et al. investigated the need for calibration in 30 healthy volunteers and compared this to previously calibrated formulas. The authors concluded, in contradiction to our results, that calibration is essential (18). This contradiction might be explained by the fact that the formula of Wu et al. (8) was based on a similar cohort and scan protocol as ours, and Verius et al. (18) compared their formula to studies with different methods, such as different age groups and scanners, than theirs. A few studies have investigated the use of 1 H-MRS to measure brain temperature in neonates, all using different formulas and TEs (7–9). Bainbridge et al. measured brain temperatures in neonates with NE on a 1.5T scanner using a TE of 288ms. The authors compared brain temperatures, calculated using two previously developed formulas from calibrations in animals, with rectal temperatures measured shortly after MRI (11,19). They concluded that both formulas correlated well with the rectal temperature, but were not perfect. The explanation of the authors is the difference in field strength: both formulas were developed at ultra-high field MR scanners in animals and the infants were scanned at 1.5T (9). Owji et al. measured brain temperatures in infants with NE with and without brain injury using a TE of 288ms on a 3.0T MRI scanner (10). They used a previously reported formula calibrated in rabbits (10,20). So, both studies used formulas calibrated in animals, which might not be most representative for neonatal studies. In this study, we therefore used the formula of Wu et al. because they calibrated the temperature in