Fibroblast Activation Protein–Targeted PET/CT with ⁶⁸Ga-FAPI for Imaging IgG4-Related Disease: Comparison to ¹⁸F-FDG PET/CT

Abstract

IgG4-related disease (RD) is characterized by lymphoplasmacytic infiltration enriched in IgG4-positive plasma cells and variable degrees of fibrosis with a characteristic storiform pattern. Since fibrosis is an important feature of IgG4-RD, we performed a prospective cohort study to evaluate the performance of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI), a recently introduced PET agent targeting fibroblast activation protein, in IgG4-RD. Methods: Twenty-six patients with IgG4-RD were recruited. All patients underwent both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT. The positive rates of the PET/CT scans in the involved organs and the uptake values were compared. Results: In a total of 136 involved organs in the 26 patients, ⁶⁸Ga-FAPI PET/CT additionally detected 18 (13.2%) involved organs in 13 (50.0%) patients, compared with ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT had a higher positive rate than ¹⁸F-FDG PET/CT in detecting involvement in the pancreas, bile duct/liver, and lacrimal gland. ⁶⁸Ga-FAPI also demonstrated significantly higher uptake than ¹⁸F-FDG in the matched disease in the pancreas, bile duct/liver, and salivary gland (P < 0.01). However, lymph node involvement with flip-flop uptake of ¹⁸F-FDG did not accumulate ⁶⁸Ga-FAPI. Conclusion: ⁶⁸Ga-FAPI might be a promising imaging agent for the assessment of IgG4-RD.