88 Chapter 5 Figure 5.1. Schematic overview of the MRI analysis pipeline. The lateral ventricle masks were inflated both 3 and 10 mm in order to classify WMH into periventricular/confluent and deep WMH. Periventricular WMHs were defined as lesions located within 3 mm from the lateral ventricular wall and extending up to 10 mm from the lateral ventricle into the white matter. Confluent WMHs were defined as lesions within 3 mm of the lateral ventricular wall and extending more than 10 mm from the lateral ventricles into the white matter. Deep WMHs were defined as lesions separated from the margins of the lateral ventricles; the distance between deep WMHs and the ventricular wall was at least 3 mm. Periventricular and confluent WMHs were further analyzed as one group because differentiation between these two subtypes would affect the WMH shape calculations. WMH lesions of less than five voxels were excluded, since WMH shape markers cannot be calculated accurately on small-volume WMHs.22 The WMH shape markers were defined based on previous studies.18 For periventricular/confluent WMHs, solidity, convexity, concavity index, and fractal dimension were determined. Solidity was calculated by dividing the lesion volume by the volume of its convex hull. Convexity was obtained by dividing the convex hull surface area by the lesions’ surface area. As a measure of roughness, the concavity index was calculated based on solidity and convexity. The fractal dimension was
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