This is an initial release of this Matlab code, which is used for sorting UK Biobank MRI data and generating fat fraction (FF) maps from segmentation volumes of this data: OPTIMATSort2023 is used for sorting the data OPTIMATSEG2FF2022 is an original version (pre 2022) used for generating FF maps from segmentations of the spine, femoral head, femoral neck, femoral epiphysis, and femoral diaphysis. Note that, in our final analyses (including all data in our publications), the femoral neck and femoral epiphysis volumes were combined into a 'total hip' (TH) volume. This original code was not used for TH volumes. OPTIMATSEG2FF_TH2022 analyses only TH regions (and has been used to date) OPTIMATSEG2FF2023 – All regions together (tested but not used yet). The release includes a Word document that describes use of the code, with additional notes for context.