Multidimensional assessment of myocardial fibrosis in coronary heart disease using 18F-FAPI-04 PET/MRI

Purpose This study aimed to explore the role of 18F-FAPI-04 PET/MRI in evaluating myocardial fibrosis in coronary heart disease (CHD) and its value in distinguishing the fibrotic status of myocardial segments. Methods A total of 47 CHD patients were enrolled in this retrospective bidirectional cohort study, including 32 patients with ST-segment elevation myocardial infarction (STEMI), 11 patients with non-ST-segment elevation myocardial infarction (NSTEMI), and 4 patients with unstable angina (UA); the latter two were classified as the non-ST-segment elevation acute coronary syndrome (NSTE-ACS) group. All the above patients underwent 18F-FAPI-04 PET/MRI examination, among which 19 STEMI patients received a second PET/MRI examination at an average of six months follow-up. Clinical, laboratory, and imaging data of these patients were collected. Differences in PET parameters between the STEMI and NSTE-ACS groups were compared; a prediction model of PET parameters for myocardial scar was constructed in STEMI patients who underwent serial PET/MRI examinations. Segmental myocardial fibrotic status was also analyzed by matching the 16-segment bullseye maps between PET and cardiac magnetic resonance (CMR) in these 19 STEMI patients. Results The standardized uptake value (SUV), target-to-background ratio (TBR), and myocardial FAPI uptake volume (MFUV) in STEMI patients were significantly higher than those in the NSTE-ACS group (P < 0.05). In STEMI patients who underwent serial PET/MRI examinations, the model incorporating SUVpeak, left ventricular end-systolic volume index (LVESVI), and peak high-sensitivity troponin I (Hs-TnIpeak) showed the best predictive performance (adjusted R2 = 0.707). The segmental SUV (SUVseg), segmental TBR (TBRseg), and late gadolinium enhancement (LGE) in FAPI+LGE+ segments were higher than those in the other groups (P < 0.001); the SUVseg and TBRseg in the FAPI+LGE- group were higher than those in the FAPI-LGE+ and FAPI-LGE- groups (P < 0.001); the LGE in the FAPI-LGE+ group was higher than in the FAPI-LGE- and FAPI+LGE- groups (P < 0.001). Conclusion 18F-FAPI-04 PET/MRI parameters can distinguish CHD subtypes, and the combined model can improve the accuracy of predicting myocardial scar. The matching analysis of 16-segment bullseye maps of PET and CMR can distinguish fibrosis stages, which provides a molecular imaging basis for CHD management.