P376 A prospective multi-model study on diagnostic performance of 18F-FAPI PET/CT in comparison with 18F-FDG PET/CT or magnetization transfer MR imaging to detect intestinal fibrosis in Crohn’s disease

Abstract

Abstract Background Accurate and early detection of Crohn's disease (CD) induced intestinal fibrosis is crucial for effective clinical management, yet it remains an unmet requirement. The magnetization transfer MR Imaging (MTI) was reported to offer high accurancy for detection of intestinal fibrosis. Recently, the utilization of fibroblast activating protein inhibitor (FAPI) PET/CT has emerged as a promising tool for assessing fibrosis. The diagnostic efficacy of 18F-FAPI PET/CT in detecting intestinal fibrosis was compared with that of 18F-FDG PET/CT and MTI. Methods Twenty-two rats were treated with TNBS for 2-4 weeks to simulate fibrosis development, and multi-model quantitative imaging was performed during a week. The mean and maximum standardized uptake values (SUVmean and SUVmax) were calculated on 18F-FAPI and 18F-FDG PET/CT, as well as the normalized magnetization transfer ratio on MTI (normalized MTR). Pathological evaluation of intestinal fibrosis was performed, and MTI was used as the imaging standard for fibrotic analysis. Imaging and pathological criteria were used to compare the diagnostic effects of fibrosis imaging parameters. Ten patients with 34 cases of intestinal stenosis were prospectively recruited to validate their diagnostic performance using the same imaging protocol. Results In patients, the accuracy of MTI (AUCs=0.90-0.91, P≤0.05) was comparable to FAPI uptake (AUCs=0.80-0.87, both P≤0.01) but higher than that of FDG uptake in distinguishing between non-to-mild and moderate-to-severe fibrosis (AUCs=0.53-0.82, P=0.01-0.36). In rats, FAPI uptake showed a rapid response to intestinal fibrosis at an early disease phase (week 0-2) and demonstrated a significant increasing trend with prolonged treatment duration (week 0-4;). In contrast, normalized MTR and FDG uptake presented only a minimal response at week 2 and did not correlate so clearly with treatment duration. Consistently, in early disease phase (rats treated till week 2), the correlations of FAPI uptake (SUVmean: R=0.69) with fibrotic scores were stronger than those of FDG uptake (SUVmean: R=0.17) and normalized MTR (R=0.52). In late disease phase (rats treated till week 3 or 4), normalized MTR (R=0.93) showed stronger correlations with fibrotic scores than FAPI uptake (SUVmean: R=0.55) or FDG uptake (SUVmean: R=0.19). Conclusion In accurately identifying early-stage intestinal fibrosis, 18F-FAPI PET/CT demonstrates vast potential and outperforms the performance of the other two imaging modalities, warranting further research. However, 18F-FAPI PET/CT offer an equal performance for characterization of intestinal fibrosis with MTI and has significant advantages compared to 18F-FDG PET/CT in the whole disease course from Crohn's disease.