68Ga-FAPI has been developed as a tumor-targeting agent as fibroblast activation protein is overexpressed in cancer-associated fibroblasts and some inflammation. 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 SAPHO than 18F-FDG PET/CT.

Synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome is a spectrum of heterogeneous diseases characterized by osteoarticular and dermatological manifestations. Inflammatory osteitis with hyperostosis is the central feature of the syndrome, typically affecting multiple areas and possibly progressing to irreversible osteoarticular damage. Owing to the relapsing-remitting disease course, the goal of management is to improve clinical symptoms and prevent disease progression. Therefore, it's meaningful to seek appropriate methods to evaluate current osteroarticular lesions. 68Ga-FAPI that targets fibroblast activation protein (FAP) is introduced in tumor imaging. However, FAP was also shown to be expressed in rheumatoid arthritis, bone lesions with acute to chronic inflammation, fibrosis and ischemic heart tissue after myocardial infarction, thus the investigators speculate that it is possible for SAPHO to be imaged with 68Ga-FAPI. The aim of this study is to evaluate the performance of 68Ga-FAPI PET/CT in SAPHO and to compare it with the performance of 18F-FDG PET/CT.

Inclusion Criteria:

• suspected or confirmed untreated SAPHO 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.