Kim Annink

246 Chapter 11 and the peak local SAR 26% lower, leading to an additional safety margin. Adult limits are therefore still safe to use. Another concern might be that the thermoregulation in neonates is immature compared to adults, so the effect of SAR values on body temperature might differ between neonates and adults (21). Neonates have less isolating subcutaneous fat and a larger surface to body weight ratio, making them more prone to develop hypothermia (21,24–26). The risk of high local peak SAR values in neonates is lower compared to adults since less power is needed in neonates to reach the same B 1 + . Furthermore, the risk of high local peak SAR is reduced by the above described safety margins (Table 1). No MRI related adverse events occurred in the infants scanned at 7.0T in this pilot study and comfort scales were stable, which are both indicators that infants did tolerate the higher main static field. The possible improvements in quality of SWI and single-shot T2WI are caused by a shorter T2-relaxation time, improved spatial resolution and increased susceptibility (5). This might enable physicians to assess the extent of injury on a microstructural level, e.g. diagnosing microbleeds, polymicrogyria and thereby improve prediction of neurodevelopmental outcome (27–29). As expected, the quality of T1WI at 7.0T was worse compared to 3.0T in infants. The T1-relaxation time increases at higher field strengths (13). Furthermore, the brains of neonates have a relatively high water content, which results in less contrast between white and grey matter. To compensate for this longer T1-relaxation time, the repetition time can be increased but this leads to a longer scanning time which is also not preferable in neonates (6,13). On the other hand, this increased T1- relaxation time enables higher quality of angiography, which in the future can help, for example, to evaluate small perforator strokes (6,10). For MRS the increased chemical shift dispersion at 7.0T results in less overlap between the different metabolite peaks, also the SNR is increased (> 2 fold). Of note is that the maximal required B 1 for MRS cannot be achieved when the infant is in -50mm position in the coil. This can happen if the shoulders do not fit in the head coil when the infant is wrapped in the vacuum matrass. In such cases, the MRS at