MR-based attenuation correction of PET images is essential for PET-MRI studies. An intensity threshold method for creating attenuation correction maps (µmaps) from 3D golden-angle radial spoiled gradient echo (radial GRE) images is presented. PET reconstructions using the Threshold µmaps, an existing radial GRE method for creating µmaps and the manufacturer Dixon VIBE µmaps are compared for quantification of 18F Sodium Fluoride (18F NaF) uptake in the aorta. Radial GRE µmaps better delineate the trachea and heart-lung boundaries. Dixon µmaps produced PET images with significantly lower aorta wall SUVmax values than radial GRE µmaps. µmaps must be characterised prior to implementation.