Abstract
Purpose: To describe the uptake of 68Gallium-labelled fibroblast activation protein inhibitor (68Ga-FAPI) in bones and joints for better understanding of the role of 68Ga-FAPI PET in benign and malignant bone lesions and joint diseases. Methods: All 129 68Ga-FAPI PET/MR or PET/CT scans from June 1, 2020 to February 20, 2021 performed at our PET centre were retrospectively reviewed. Foci of elevated 68Ga-FAPI uptake in bones and joints were identified. All lesions were divided into malignant and benign disease. Benign lesions included osteofibrous dysplasia, periodontitis, degenerative bone diseases, arthritis, and other inflammatory or trauma-related abnormalities. The number, locations and SUVmax of all lesions were recorded and analysed. Results: Elevated uptake of 68Ga-FAPI in/around bones and joints were found in 82 cases (63.57%). A total of 295 lesions were identified, including 94 (31.9%) malignant lesions (all were metastases) and 201 (68.1%) benign lesions. The benign lesions consisted of 13 osteofibrous dysplasia, 48 degenerative bone disease, 33 periodontitis, 56 arthritis, and 51 other inflammatory or trauma-related abnormalities. Spine, shoulder joint, alveolar ridge, and pelvis were the most commonly involved locations. Bone metastases were mainly distributed in the spine, pelvis and ribs. Among benign diseases, periodontitis and arthritis are site-specific. The mean SUVmax of bone metastases was significantly higher than that of benign diseases (7.14 ± 4.33 vs. 3.57 ± 1.60, p < 0.0001), but overlap existed. The differences in SUVmax among subgroups of benign diseases were statistically significant (p < 0.0001), with much higher uptake in periodontitis (4.45 ± 1.17). Conclusion: 68Ga-FAPI accumulated in both bone metastases and some benign diseases of bones and joints. Although the uptake of 68Ga-FAPI was often higher in bone metastases, this finding cannot be used to distinguish between benign and malignant lesions.