68Ga-FAPI has been developed as a tumor-targeting agent as fibroblast activation protein is overexpressed in cancer-associated fibroblasts and some inflammation, such as IgG4-related disease. Therefore, this prospective study is going to investigate whether 68Ga-FAPI PET/CT may be superior for disease activity assessment and follow-up of psoriatic arthritis than 18F-NAF PET/CT.

Psoriatic arthritis (PsA) is a chronic inflammatory disease that develops in up to 30% of patients with psoriasis and characterized by diverse clinical features including peripheral and axial arthritis, enthesitis, dactylitis and nail dystrophy, leading to impaired function and reduced quality of life. Positron emission tomography (PET) allows for highly sensitive depiction of targets at the molecular level and can be used to specifically visualize immune cells of interest through the use of specific tracers. In this study, we used two tracers: 68Ga-fibroblast activation protein inhibitor (FAPI) and 18F-sodium fluoride (18F-NaF) to evaluate both joint inflammation and bone metabolism in patients with PsA. And the study is going to investigate whether 68Ga-FAPI PET/CT may be superior for disease activity assessment and follow-up of psoriatic arthritis than 18F-NAF PET/CT.

Inclusion Criteria:

• fulfilled the 2006 Classification Criteria for Psoriatic Arthritis (CASPAR)
• 18F-NAF PET/CT within two weeks
• signed written consent.

Exclusion Criteria:

• pregnancy
• breast feeding
• known allergy against FAPI
• any medical condition that in the opinion of the investigator may significantly interfere with study compliance.