115 Distinct brain MRI phenotypes and their association with long-term dementia risk 6 Figure 6.1 Flowchart Illustrating the Inclusion and Exclusion of Participants. 6.3.2 Standard protocol approvals, registrations, and patient consents The study was approved by the Icelandic National Bioethics Committee, VSN:00063, and the institutional review board responsible for the National Institute on Aging research; all participants signed for informed consent. 6.3.3 MRI Scanning protocol A baseline brain MRI scan was acquired on a 1.5 T Signa TwinSpeed system (General Electric Medical Systems, Waukesha, WI). The MRI protocol included a fluid-attenuated inversion recovery (FLAIR) sequence (repetition time = 8000 milliseconds; time to echo = 100 milliseconds; inversion time = 2000 milliseconds; field of view = 220 mm; voxel size = 0.86 × 0.86 × 3.00 mm3; interleaved slices) and a T1-weighted sequence (repetition time = 21 milliseconds; time to echo = 8 milliseconds; field of view = 240 mm; slice thickness = 1.5 mm; voxel size = 0.94 × 0.94 × 1.50 mm3).11 A T2*-weighted gradient echo-type echo planar sequence (time to echo = 50 milliseconds; repetition time = 3050 milliseconds; flip angle = 90°; field of view = 220 mm; matrix = 256 × 256) and a proton density/T2-weighted fast-spin echo sequence (time to first echo = 22 milliseconds; time to second echo = 90 milliseconds; repetition time = 3220 milliseconds; echo train length = 8; flip angle = 90°; field of view = 220 mm; matrix = 256 × 256) were also part of the MRI protocol.
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