Design: Subjects with MAS will be recruited from participants in 98-D-0145 Screening and Natural History of Patients with Polyostotic Fibrous Dysplasia and the McCune-Albright Syndrome (PI: Michael T. Collins, MD). Only participants in protocol (98-D-0145) who provided self-consent without a legally authorized representative will be recruited. Brain PET scans will be performed by measuring metabolite-corrected arterial input function. No blood sampling will be performed for whole body scans.