Kim Annink

14 Chapter 1 focuses mainly on neuroimaging, one should keep in mind that decisions about clinical care are always based on the triad of neuroimaging, neurophysiology and clinical measures. The gold standard for neuroimaging in neonates with HIE is MRI. There are several MRI techniques that are known to be associated with neurodevelopmental outcome. First of all, brain injury on conventional, T1- and T2-weighted imaging can be scored with visual scoring methods. Both the scoring systems of Barkovich et al. and Weeke et al. are associated with neurodevelopmental outcome and are easy to use in clinical practice (20,21). Diffusion Weighted Imaging (DWI) is a more quantitative MRI modality and can provide additional information. DWI measures the diffusion of water molecules between the cells in the brain. In case of HIE, cytotoxic edema may lead to swelling of the neurons and thereby to diffusion restriction of the water molecules (high signal on DWI) (22–24). This diffusion restriction can be quantified on the apparent diffusion coefficient (ADC) map, in which the T2 shine through signal is excluded. Alderliesten et al. showed that ADC values below 1031*10 -6 mm 2 /s in the basal ganglia/thalami area have a sensitivity of 78% and specificity of 95% for an adverse outcome at two years of age (22). It is important to note that the reliability of ADC values is highly dependent on timing: seven to ten days after the hypoxic event there is a pseudo- normalization of the ADC values (23). However, if the MRI is performed too early after birth, the cytotoxic edema might not be fully developed and yet be visible. Therefore, the optimal timing for DWI is between day three and seven after birth. Magnetic Resonance Spectroscopy (MRS) is another frequently used MRI sequence in infants with HIE. MRS enables us to measure the concentrations of different types of metabolites in the brain (25). Higher lactate peaks are known to be associated with brain injury, but also lower N-acetylaspartate (NAA) levels, which is a neuronal marker for healthy neurons, are associated with neuronal loss. Alderliesten et al. showed that the area under the curve of the lactate/NAA ratio for predicting two year outcome was 0.89 (25). Arterial Spin Labelling (ASL) is an MRI technique showing the perfusion of the brain. In infants with HIE, hyperperfusion of the brain is associated with an