Positron emission tomography (PET) and magnetic resonance imaging (MRI) images of a patient with high disease activity. Coronal [18F]FDG (a) PET and (b) PET- computed tomography (PET-CT) and coronal [11C](R)PK11195 (c) PET and (d) PET-CT images of sacroiliac joints with no tracer uptake. (e) Coronal/oblique MRI (short-tau inversion recovery) of sacroiliac joints of the same patient. Bone marrow edema is present in both sacroiliac joints (indicated by red arrows). [11C](R)PK11195, PK11195 [(R)-1-(2-chlorophenyl)-N-methyl-N(1-methyl-propyl)-3-soquinoline carboxamide]; [18F]FDG, [18F]-fluoro-2-deoxy-D-glucose.