Kim Annink

118 Chapter 6 MRI at 10 years of age MRI scans were conducted at a 3.0T MRI scanner without sedation (Philips Healthcare, Best, the Netherlands). The scan protocol contained among others 3D-T1-weighted imaging (TE=4.6ms; TR=10ms; slice-thickness=0.8mm, no gap), fluid attenuated inversion recovery (FLAIR) (TE=120ms; TR=10000ms; slice- thickness=4mm, no gap) and DWI (TE=96; TR=3317; using 13 non-diffusion weighted images and 111 diffusion weighted images with b-values of 500 s/mm 2 (15), 1000 s/ mm 2 (32) and 2000 s/mm 2 (64)). In addition, a single non-diffusion weighted image was acquired in the opposite phase-encoding direction. MRI – scoring The 3D-T1-weighted and FLAIR images were scored according to the scoring method of van Kooij et al.: 1) no injury, 2) solitary white matter lesions and/or (focal) thinning of the corpus callosum, 3) watershed injury, 4) deep grey matter injury or 5) focal infarction (22). Mammillary bodies at 10 years of age were scored based on the sagittal plane of the 3D-T1-weighted MRI. The mammillary bodies were categorized as normal if there was no atrophy or if they appeared smaller but were still detectable. Mammillary bodies were scored as atrophic if they were not visible (Figure 1). Two authors reached agreement on all cases. A third reader scored 18 random patients to determine the interrater variability. MRI – volumetric measurements Volumetric segmentation of 3D-T1-weighted MR scans was performed using Freesurfer version 6.0.0 (23). Segmentation of the subcortical deep grey matter structures and parcellation of the white matter and cortex was based on signal intensity differences. Images with large movement artefacts were excluded. This resulted in segmentation of 20 subcortical volumes and parcellation of 40 white matter and 40 cortical volumes. MRI scans with topological defects, skull strip errors or white matter errors were manually corrected prior to segmentation. For more elaborative details of this method, we refer to earlier publications (23). Total volumes refer to the uncorrected volume in ml and relative volumes to the volume of the structure as a percentage of total brain volume (TBV) excluding cerebral spinal fluid.