Characterizing Normal Variant [68Ga]Ga-FAPI-46 Uptake in the Epididymis

The biodistribution of fibroblast activation protein inhibitor (FAPI) PET tracers includes the kidneys, bladder, uterus, breast, muscles, and bone marrow. We describe its occasional uptake patterns in the epididymis. Methods: Epididymal [68Ga]Ga-FAPI-46 uptake was retrospectively analyzed in 55 PET/CT studies of 55 men. Uptake intensity (SUV), pattern (diffuse, focal, or multifocal), laterality, and location (epididymal head with or without body/tail) were analyzed. Electronic medical records were reviewed to determine the presence of epididymisrelated disease. Results: Epididymal [68Ga]Ga-FAPI-46 uptake was observed in 8 of 55 (15%) subjects, with bilateral epididymal head uptake in all cases and epididymal body/tail uptake in 6 of 8 (75%) cases, 5 of 6 (83%) bilaterally and 1 of 6 (17%) unilaterally. The average SUVmax was greater in the epididymal heads than in the epididymal bodies/tails, with an SUVmax of 4.1 versus 3.0 (P , 0.001). No subject had epididymal disease related to the uptake. Conclusion: [68Ga]Ga- FAPI-46 uptake in the epididymis occurs occasionally and does not appear related to epididymal disease.