Assessment of temporal, intra-individual variability of 68Ga-FAPI- and 18F-FDG-uptake in joints and healthy tissue

Ziel/Aim: 18F-FDG-PET and 68Ga-FAPI-PET are frequently used in cancer diagnostics, but also display degenerative changes in joints. To evaluate intra-individual variability of joint-associated and physiological 68Ga-FAPI and 18F-FDG uptake, we analyzed temporal differences between the uptake in normal tissue (n.t.) and joints during multiple follow-up examinations using both tracers.

Methodik/Methods: Patients underwent multiple static 68Ga-FAPI-46 PET/CT and 18F-FDG PET/CT (60 min post injection) as part of oncological follow-up examinations. SUVmax and SUVmean were generated from VOIs of n.t. and joints using PMOD software. We analyzed patientwise in- and decrease of SUVmax/mean (delta SUV values) relative to the prior examination.

Ergebnisse/Results: 22 patients were examined by 68Ga-FAPI-PET (in av. 3 subsequent examinations) and 30 patients were examined by 18F-FDG tracer (in av. 4 recurrent examinations). Comparing 68GA-FAPI, we observed an average delta SUVmax/mean of 41.61%+/- 66.17% / 29.88%+/- 47.5% in joints and of 35.67%+/- 46.46% / 37.18%+/- 56.92% in n.t.s. In subsequent FDG examinations, we observed an average delta SUVmax/mean of 25.28%+/- 33% / 17.82%+/- 23.66% in joints and 49.47%+/- 45.30% / 26.41%+/- 44.24% in n.t.. We observed the in av. highest delta SUVmax in the right glenohumeral joint with 59.77+/- 64.29 and SUVmean in the left acromioclavicular joint with 45.35%+/- 53.2% in av. in the FAPI PET/CT. In the FDG Pet/CTs we observed the in av. highest delta SUVmax also in the right gc joint with 36.55%+/- 32.74% and with 27.21%+/- 34.55% the highest SUVmean in av. in the left ac joint. In n.t. we observed an uptake of in av. 17.61%+/-31.1% in the blood in the SUVmax FAPi surveys and 37.34%+/- 62.88% in the liver. In the FDG observations there was a traceruptake of 18.19%+/- 22.19% in av. in the blood and 29.26%+/- 28.02% in the liver in the SUVmax observations.

Schlussfolgerungen/Conclusions: Both, FAPI 46 and FDG have a more fluctuant uptake in joints than in n.t.. This is likely to be caused by individual factors such as age or degenerative changes in joints, which are displayed by changes in glucose metabolism and presence of FAP-positive fibroblasts. In n.t.s, FDG showed higher temporal variability than FAPI, which may reflect higher variability of glucose metabolism than of FAP-expression in different tissues.

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Artikel online veröffentlicht:
12. März 2025