Kim Annink

219 Measurement of brain temperature using MRS INTRODUCTION Over the past decades, magnetic resonance imaging (MRI) has become one of the most important neuroimaging techniques to assess brain injury in high-risk neonates (1,2). MRI has shown to be more sensitive to diagnose brain injury in neonates compared to computed tomography or cerebral ultrasound (2,3). Furthermore, no radiation is used making it safe to use in neonates (2). Although MRI is safe in neonates, there are some potential risks that should be considered, such as an increase in the temperature of the body and brain (4,5). To conduct an MRI, pulses of radiofrequency (RF) energy are applied to create images (1). This RF energy is partly absorbed by the tissue of the patient, which can potentially lead to an increase in temperature (1). The amount of RF energy in Watt absorbed by 1 kg of tissue of the patient is called the specific absorption rate (SAR). So, a higher SAR increases the risk of a rise in body temperature. Therefore, the SAR level is monitored by the MR scanner and scanning is limited when SAR levels are about to exceed the maximum allowed SAR limits as specified by the FDA guidelines (6). However, little is known about the exact effect of the SAR on the brain temperature of neonates during MRI. The rectal temperature of term and preterm neonates seems to be similar before and after MRI (4,7). Although body and brain temperatures are correlated, it has not yet been fully elucidated what the exact effect is of MRI on the brain temperature. In addition, the temperature management during MRI is less optimal due to the low temperature in the MR room (18°C) which might also decrease body temperature if no temperature-controlled MR incubator can be used (5). Recent studies have shown that it is possible to non-invasively measure brain temperature with proton Magnetic Resonance Spectroscopy ( 1 H-MRS) (8–10). The chemical shift of water is temperature dependent, whereas the chemical shift of some metabolites in the brain tissue such as N-acetyl aspartate (NAA) is not. This chemical shift difference (ΔH 2 O-NAA) can be used to determine the temperature with an accuracy of 0.5 °C in 1.5T and 3.0T systems (8,11). The primary aim of this study was to assess the feasibility of measuring brain temperature non-invasively using 1 H-MRS in infants with neonatal encephalopathy (NE) following perinatal asphyxia. The clinical feasibility was investigated by 10