Comparative Analysis of 18F-FAPI and 18F-FDG PET/CT in Evaluation of Intestinal Lesions and Disease Activity in Ulcerative Colitis

PURPOSE: Accurate evaluation of intestinal lesions and severity assessment of ulcerative colitis (UC) are crucial for therapeutic strategies and prognosis. This study aims to compare the efficacy of 18 F-FAPI and 18 F-FDG PET/CT in the evaluation of intestinal lesions and disease activity assessment of UC. METHODS: This is a prospective cohort study, and patients with newly diagnosed or relapsed UC were enrolled. All participants underwent 18 F-FAPI PET/CT, 18 F-FDG PET/CT, abdominal contrast-enhanced CT, and colonoscopy within 1 week. Mayo Endoscopic Subscore (MES) was used as the reference standard for identification and severity assessment of intestinal lesions. Target-to-background ratio (TBR) of each segment in 18 F-FAPI/ 18 F-FDG PET/CT and global 18 F-FAPI/ 18 F-FDG PET/CT score were computed to represent the activity of independent segments and all segments, respectively. Before examinations, partial Mayo score was calculated based on clinical manifestations of patients, and levels of C-reactive protein, interleukin-6, erythrocyte sedimentation rate, platelet, and hemoglobin were determined. Finally, all data were analyzed to compare the efficacy of 18 F-FAPI and 18 F-FDG PET/CT in the evaluation of intestinal lesions and disease activity in UC. RESULTS: A total of 113 intestinal segments (including 90 lesion segments) were evaluated among 23 participants. Through receiver operating characteristic (ROC) analysis, 18 F-FAPI PET/CT showed significantly superior performance in detecting intestinal lesions compared with 18 F-FDG PET/CT ( P = 0.046) and abdominal contrast-enhanced CT ( P = 0.007). The correlations between FAPI-TBR and MES ( R2 = 0.75) and abdominal contrast-enhanced CT score ( R2 = 0.55) were stronger than those of FDG-TBR. 18 F-FAPI PET/CT showed superior discriminative capacity across different disease activity levels at both segmental ( P < 0.001) and patient-level ( P < 0.05) in intergroup comparison. The global 18 F-FAPI PET/CT score was significantly correlated with other activity indicators ( r = 0.49-0.76). Moreover, 18 F-FAPI PET/CT was also significantly superior to 18 F-FDG PET/CT ( P < 0.001) and abdominal contrast-enhanced CT ( P = 0.001) in detecting active lesions according to ROC analysis. CONCLUSIONS: The efficacy of 18 F-FAPI PET/CT in the evaluation of intestinal lesions and disease activity assessment of UC was superior to that of 18 F-FDG PET/CT. 18 F-FAPI PET/CT also correlated well with endoscopy, abdominal contrast-enhanced CT, clinical manifestations, and biomarkers. Therefore, 18 F-FAPI PET/CT may be a promising method for noninvasive assessment of disease activity of UC.