87 White matter hyperintensity shape is associated with long-term dementia risk 5 finding, for example, brain tumor detected on MRI, an additional follow-up was made with a phone call to the general practitioner or the emergency center at the hospital. The participants were tracked for dementia diagnosis through vital statistics and hospital records and by the nursing home and home-based resident assessment instrument.16 The average time to follow-up for dementia outcome (yes/no) was 9.9 ± 2.6 years (interquartile range 3.1 years). Participants were followed from the date of the baseline MRI scan until occurrence of dementia, loss to follow-up, or end of follow-up. Loss to follow-up means that the participants died or could not be contacted. The dementia follow-up was concluded in 2015. 5.3.2 MRI imaging protocol The participants underwent a baseline brain MRI scan acquired on a 1.5 Tesla Signa Twinspeed system (General Electric Medical Systems, Waukesha, Wisconsin, USA). The imaging protocol included a FLAIR sequence (repetition time = 8000 ms; time to echo = 100 ms; field of view = 220 mm; voxel size = 0.86 × 0.86 × 3.00 mm3) with 3-mm-thick interleaved slices and a T1-weighted sequence (repetition time = 21 ms; time to echo = 8 ms; field of view = 240 mm; slice thickness = 1.5 mm; voxel size = 0.94 × 0.94 × 1.50 mm3).17 5.3.3 MRI analysis pipeline Mean values per WMH shape marker (solidity, convexity, concavity index, fractal dimension for periventricular/confluent WMH; fractal dimension and eccentricity for deep WMH), as well as WMH volumes, were calculated per participant with a method developed in-house.18 An overview of the image processing pipeline is given in Figure 5.1. The FLAIR and T1 images were registered using Elastix19 in Python (version 3.8; Phyton Software Foundation, Wilmington, DE, USA). WMHs were segmented automatically using the registered FLAIR images in the LST toolbox20 in SPM 12 (Wellcome Trust Centre for Neuroimaging, London, UK) for MATLAB (version 9.9; MathWorks, Natick, MA, USA). A modified, SPM12-based version of the ALVIN script21 was used to segment the lateral ventricles from the T1-weighted images.
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