Purpose This study aimed to assess the diagnostic performance of [18F]FAPI-42 PET/CT and compare it with that of 2-[18F]FDG PET/CT in patients with differentiated thyroid cancer (DTC) with biochemical elevations in Tg or anti-Tg antibodies. Methods A total of 42 patients with DTC with biochemical elevations in Tg or anti-Tg antibodies underwent [18F]FAPI-42 PET/CT as part of this study; of which, 11 additionally underwent 2-[18F]FDG PET/CT within 7 days. Images were semi-quantitatively and visually interpreted, and the quantity, location, and uptake values of lesions were noted. The diagnostic capacity of [18F]FAPI-42 PET/CT and biomarkers affecting the uptake of [18F]FAPI-42 were evaluated. In addition, the diagnostic performance and uptake of [18F]FAPI-42 and 2-[18F]FDG were compared, and the correlation between lesion diameter and quantitative parameters was investigated. Results A total of 161 lesions were detected in 27 (64%) patients on [18F]FAPI-42 PET/CT. FAPI-positive local recurrence showed the highest uptake intensity, followed by lymphatic, other site-associated (bone and pleura), and pulmonary lesions (mean SUVmax, 4.7 versus 3.7 versus 3.0 versus 2.2, respectively; P < 0.0001). The levels of TSH, Tg, and Tg-Ab did not affect the uptake value of lesions (median SUVmax: 2.4 versus 3.2, P = 0.56; 2.9 versus 2.4, P = 0.0935; 2.8 versus 2.6, P = 0.0525, respectively). A total of 90 positive lesions were detected in 7 patients using both modalities. All positive lesions showed statistically higher uptake of 2-[18F]FDG than that of [18F]FAPI-42 (SUVmax, 2.6 versus 2.1; P = 0.026). However, the SUVmax of [18F]FAPI-42 was higher than that of 2-[18F]FDG in local recurrences and lymphatic lesions (SUVmax, 4.2 versus 2.9 and 3.9 versus 3.4, respectively; P > 0.05). Conclusion [18F]FAPI-42 can be used for detecting lesions and reflecting FAP expression during local recurrence and metastasis in patients with DTC with biochemical elevations in Tg or anti-Tg antibodies. The diagnostic performance of [18F]FAPI-42 PET/CT is comparable with that of 2-[18F]FDG PET/CT in such patients.

Vertebral brucellosis is a relatively rare disease that usually emerges in animal husbandry areas. We report a case that brucellosis of lumbar vertebral body showed an intense uptake of FAPI on 18 F-FAPI PET/CT, which mimics to malignant lesions or vertebral tuberculosis. It is an interesting finding to realize that vertebral brucellosis is also one of the reasons for intense uptake of FAPI.

PurposeTo calculate the physiological uptake of various tissues in patients with cancer using 18F-AlF-NOTA-FAPI-04 (18F-FAPI-04) and 18F-AlF-NOTA-FAPI-42 (18F-FAPI-42) PET/CT and to compare the variation in standard uptake values between the two scans.Materials and methodsThis retrospective analysis included 40 patients with cancer who underwent 18F-FAPI; the first 20 patients received 18F-FAPI-04 PET/CT and the remaining 20 patients received 18F-FAPI-42 PET/CT. A total of 49 normal tissues, including the brain (cerebrum/cerebellum), parotid and submandibular glands, palatine tonsils, and thyroid, were identified on CT images. For these normal tissues, maximum standardized uptake value (SUVmax) and mean standardized uptake value (SUVmean) were calculated. We also compared the SUVmean of identical tissues to explore the difference in biodistribution between the two radiotracers.ResultsThe accumulation of 18F-FAPI-04 and 18F-FAPI-42 showed an analogous pattern. High uptake of both radiotracers in the gallbladder, uterus, submandibular gland, and renal pelvis was demonstrated (range: SUVmax, 4.01–5.75; SUVmean, 2.92–4.22). Furthermore, the uptake of bony tissues was slightly higher in 18F-FAPI-42 than in 18F-FAPI-04 (range: SUVmean, 0.4 ± 0.22–0.9 ± 0.34 and 0.3 ± 0.24–0.7 ± 0.18, respectively, p &lt; 0.05), while the uptake of some soft tissues was higher in 18F-FAPI-04 than in 18F-FAPI-42 (range: SUVmean, 0.9 ± 0.24–1.5 ± 0.35 and 0.9 ± 0.26–1.2 ± 0.37, respectively, p &lt; 0.05).ConclusionsBoth radioligands exhibited similar physiological uptake of normal tissues in patients with cancers. In addition, 18F-FAPI-42 demonstrated higher uptake of bone tissues than 18F-FAPI-04 while showing lower uptake of soft tissues than 18F-FAPI-04.

Purpose This study aimed to assess the diagnostic performance of [18F]FAPI-42 PET/CT and compare it with that of 2-[18F]FDG PET/CT in patients with differentiated thyroid cancer (DTC) with biochemical incomplete response. Methods A total of 42 patients with DTC with biochemical incomplete response underwent [18F]FAPI-42 PET/CT as part of this study; of which, 11 additionally underwent 2-[18F]FDG PET/CT within 7 days. Images were semi-quantitatively and visually interpreted, and the quantity, location and uptake values of lesions were noted. The diagnostic capacity of [18F]FAPI-42 PET/CT and biomarkers affecting the uptake of [18F]FAPI-42 were evaluated. In addition, the diagnostic performance and uptake of [18F]FAPI-42 and 2-[18F] FDG were compared, and the correlation between lesion diameter and quantitative parameters was investigated. Results A total of 161 lesions were detected in 27 (64%) patients on [18F]FAPI-42 PET/CT. FAPI-positive recurrent lesions showed the highest uptake intensity, followed by lymphatic, other site-associated (bone and pleura) and pulmonary lesions (mean SUVmax, 4.7 versus 3.7 versus 3.0 versus 2.2, respectively; p < 0.0001). The levels of TSH, Tg, and Tg-Ab did not affect the uptake value of lesions (median SUVmax: 2.4 versus 3.2, p = 0.56; 2.9 versus 2.4, p = 0.0935; 2.8 versus 2.6, p = 0.0525, respectively). A total of 90 positive lesions were detected in 7 patients using both modalities. All positive lesions showed statistically higher uptake of 2-[18F]FDG than that of [18F]FAPI-42 (SUVmax, 2.1 versus 2.6; p = 0.026). However, the SUVmax of [18F]FAPI-42 was higher than that of 2-[18F]FDG in recurrent and lymphatic lesions (SUVmax, 4.2 versus 2.9 and 3.9 versus 3.4, respectively; p > 0.05). Conclusion [18F]FAPI-42 can be used for detecting lesions and reflecting FAP expression during recurrence and metastasis in patients with DTC with biochemical incomplete response. The diagnostic performance of [18F]FAPI-42 PET/CT is comparable with that of 2-[18F]FDG PET/CT in such patients.