Kim Annink

262 Chapter 12 Part III: innovative neuroimaging techniques There has been a rapid innovation in the field of MRI techniques in the past years: more sequences have been developed and applications have been found. It is important to consider the safety of new MRI methods. One of the risks of MRI is an increase of temperature because of the specific absorption rate (SAR), which is the amount of energy absorbed by the body (59). The effect of SAR on brain temperature is rarely studied, but would help to gain more knowledge on safety of innovative MRI techniques. Therefore an easy method to measure brain temperature is needed. In chapter ten we studied the feasibility of measuring brain temperature using 1 H-MRS in infants with HIE following perinatal asphyxia. First, we validated a previously reported formula to calculate brain temperature using 1 H-MRS (60) and a formula we made based on phantom calibration. Afterwards, we included (near-) term infants with HIE and determined brain temperature of these infants using short and long echo time 1 H-MRS. Based on these measurements we were able to conclude that brain temperature did not differ significantly by using the earlier reported formula or the formula based on calibration and neither between short and long echo time 1 H-MRS. All brain temperatures remained within the normal range. This is important since it implies that the formula of Wu et al. can be used in multiple centers using short or long echo time 1 H-MRS without calibration (60). An easy and validated method to measure brain temperature enables researchers and clinicians to collect more safety data during MRI. Methods to measure safety in neonatal neuroimaging are even more important while investigating safety and feasibility of ultra-high field MRI. In adults ultra-high field MRI has increased diagnostic value and shows more details of the arterial and venous vasculature and anatomy (61). This might also be beneficial in neonates at risk of brain injury, such as neonates with unexplained seizures or neonates with suspected microgyria or metabolic disorders. 7.0 Tesla (T) MRI has never been performed in neonates, so feasibility and safety should be investigated in a pilot study before the additional diagnostic value and clinical impact of 7.0T MRI can be determined in a larger study. In chapter eleven we investigated the feasibility of ultra-high field MRI in neonates between term (equivalent age) and three months post-term and provided the first MR images of neonates at 7.0T MRI. SAR simulations showed that SAR limits in a