Kim Annink

220 Chapter 10 determining whether brain temperatures calculated with a previously developed formula were similar to brain temperatures calculated with a formula developed using phantom calibration. Furthermore, brain temperatures measured using short (36ms) and long (288ms) echo time (TE) 1 H-MRS were compared. The secondary aim was to compare the MRS-derived brain temperature in infants with NE with rectal temperature before and after MRI. METHODS Design and subjects In this single-center retrospective study, (near-)term infants with NE following perinatal asphyxia (referred to as NE) who were admitted to the level III Neonatal Intensive Care Unit (NICU) of the University Medical Center Utrecht (UMCU) between December 2011 and June 2017 were eligible for inclusion. Neonates born with a gestational age of ³ 36 weeks, diagnosed with NE following perinatal asphyxia and treated with therapeutic whole-body hypothermia according to international guidelines (12) were included. Furthermore, it was essential that 1 H-MRS of sufficient quality and rectal temperature data (not more than 3 hours) before and after the MRI were available for analyses. Infants with metabolic or genetic abnormalities were excluded. All infants were included in the PharmaCool study (www.trialregister. nl NL2421) (13) or 2-STEP study (www.trialregister.nl NL5089) (14) and informed consent of parents for the use of their infants data was available. These studies were approved by the Ethical Committee of the UMCU. Clinical parameters All baseline characteristics and rectal temperature data were retrospectively obtained from electronic medical records. The rectal temperatures closest, and not more than 3 hours, before and after MRI were collected. These temperatures were all measured on the NICU using a rectal thermometer or using a rectal temperature probe for continuous temperature monitoring. Validation of the formula The local brain temperature was calculated by the formula of the study of Wu et al. (8): T=(-102.89*ΔH 2 O-NAA)+308.64; with T as local brain temperature in degrees Celsius and ΔH 2 O-NAA being the difference between the spectral positions of water and NAA in parts per million (ppm). This formula is developed in infants with NE using short TE 3.0T MRI.