Pitfalls and Common Findings in<sup>68</sup>Ga-FAPI PET: A Pictorial Analysis
Lukas Kessler, Justin Ferdinandus, Nader Hirmas, Fadi Zarrad, Michael Nader, David Kersting, Manuel Weber, Sandra Kazek, Miriam Sraieb, Rainer Hamacher, Katharina Lueckerath, Lale Umutlu, Wolfgang P. Fendler, Christoph Rischpler
Abstract
<b>Introduction: </b> 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. <b>Methods and materials: </b> 91 patients underwent whole-body PET/CT with either FAPI-04 (<i>N</i> = 25) or FAPI-46 (<i>N</i> = 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 SUV<sub>max</sub>, SUVmean and SUVpeak was measured. <b>Results:</b> 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 SUV<sub>max</sub> 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 SUV<sub>max</sub> 12.2 ± 7.3 and uptake correlated negatively with age (SUV<sub>max</sub> r = -0.6, p<0.01; SUVpeak r = -0.57, p<0.01; SUVmean r = -0.58, p<0.01). <b>Conclusion:</b> 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.