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 and inflammatory bowel disease. Some researches identified FAP expression in synovial samples taken from both rheumatoid arthritis and osteoarthritis patients.Thus this prospective study is going to investigate whether 68Ga-FAPI PET/CT may be superior for diagnosis, therapy response assessment and follow-up of arthritis than 18F-FDG PET/CT.

Arthritis is a term used to mean any disorder that affects the joints. The two most common forms of arthritis are osteoarthritis and rheumatoid arthritis.Rheumatoid arthritis is an autoimmune chronic inflammatory disease of unknown etiology and is characterized by chronic inflammation of the joint capsule's synovial membrane. This chronic inflammation ultimately destroys the underlying cartilage and bone. Activated fibroblast-like synoviocytes (FLS) line the synovial membrane and are a prominent cell type responsible for inflammation and joint destruction. Osteoarthritis is characterized by degradation of joint cartilage. Studies demonstrate chondrocytes expressed FAP and that chondrocyte FAP expression was elevated in patients with osteoarthritis. Other researches identified FAP expression in synovial samples taken from both rheumatoid arthritis and osteoarthritis patients. However, FAP expression was greater in samples taken from refractory rheumatoid arthritis patients in comparison to end-stage osteoarthritis patients.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 and inflammatory bowel disease. Recently the investigators have published an article of the application of 68Ga-FAPI in IgG4-related disease which showed it was more sensitive than FDG in detecting a certain type of inflammations. Thus this prospective study is going to investigate whether 68Ga-FAPI PET/CT may be superior for diagnosis, therapy response assessment and follow-up of arthritis than 18F-FDG PET/CT.

Inclusion Criteria:

• suspected or confirmed untreated arthritis patients;
• 18F-FDG PET/CT within two weeks;
• signed written consent.

Exclusion Criteria:

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