Pitfalls and common findings in 68Ga-FAPI-PET - A pictorial analysis.

Abstract

Introduction: Fibroblast activation protein inhibitor positron emission tomography (FAPI-PET) is a new tool in the diagnostic workup of cancer. With growing volume of applications pitfalls and common findings need to be considered for Ga-68-FAPI-PET image interpretation. The aim of this study was to summarize common findings and report pitfalls in Ga-68-FAPI-PET. Methods and materials: 91 patients underwent whole-body PET/CT with either FAPI-04 (N = 25) or FAPI-46 (N = 66). Findings were rated in a consensus session of two experienced readers. Pitfalls and common findings were defined as focal or localized uptake above background and categorized as unspecific / non-malignant and grouped into degenerative, muscular, scarring / wound-healing, uterine, mammary glands and head-and-neck findings. Frequency of findings was reported on a per-patient and per-group basis and SUVmax, SUVmean and SUVpeak was measured. Results: Non-tumor specific tracer uptake was found in 81.3 % of patients. The most frequent finding was tracer uptake in degenerative lesions (51.6%) with mean SUVmax 7.7 ± 2.9 and head-and-neck (45.1%) findings. Except for salivary glands, the uptake values did not differ between 10 and 60 min p.i. in most findings. Uterine uptake was found in most women (66.7%) with mean SUVmax 12.2 ± 7.3 and uptake correlated negatively with age (SUVmax r = -0.6, p<0.01; SUVpeak r = -0.57, p<0.01; SUVmean r = -0.58, p<0.01). Conclusion: Pitfalls include non-tumor specific Ga-68-FAPI uptake in degenerative lesions, muscle, head-and-neck, scarring, mammary glands or uterus. Here we summarize findings to inform readers at centers introducing Ga-68-FAPI-PET to avoid common mistakes.