Clinical significance of diffuse [F] AlF-NOTA-FAPI-04 uptake in the thyroid on PET/CT imaging.

BACKGROUND

Many patients undergoing [F] AlF-NOTA-FAPI-04 (F-FAPI) PET/CT demonstrated diffuse thyroid uptake. These findings created challenges for accurate interpretation due to the limited understanding of physiological and non-oncologic causes of diffuse F-FAPI uptake in the thyroid. This retrospective study examined patients who underwent F-FAPI PET/CT imaging with diffuse thyroid uptake. It quantitatively assessed normal thyroid uptake, compared F-FAPI uptake between normal and diseased thyroids, and explored potential associations with diffuse thyroid uptake. The study may improve the accuracy of F-FAPI PET/CT interpretation for thyroid and facilitate appropriate management of diffuse thyroid uptake on F-FAPI PET/CT.

RESULTS

A total of 38 patients were included in this study based on the inclusion criteria. The mean SUVmax, SUVmean, and TBR of normal thyroid were 7.09 ± 3.83, 4.24 ± 2.25 and 3.93 ± 1.73, respectively. Quantitative analysis revealed no significant asymmetry in F-FAPI uptake between the right and left thyroid lobes (SUVmax: right 6.69 ± 2.96 vs. left 6.54 ± 3.28, p = 0.84; SUVmean: right 4.19 ± 1.73 vs. left 4.18 ± 1.97, p = 0.98), consistent with the diffuse uptake pattern observed. There was no significant correlation between Hashimoto thyroiditis, serum TSH levels, and the degree of diffuse thyroid uptake (all p > 0.05 for SUVmax, SUVmean, and TBR). Furthermore, no association was observed between sex, age, immunotherapy, and diffuse thyroid uptake (p > 0.05).

CONCLUSIONS

Diffuse uptake of F-FAPI in the thyroid may not significantly relate to Hashimoto thyroiditis or abnormal serum TSH levels. Lesions on F-FAPI PET/CT scans might be hard to detect due to the moderate uptake in normal thyroid tissue.