Hybrid Cardiac ⁶⁸Ga-FAPI-4 PET/MRI in Dilated Cardiomyopathy: A Feasibility and Pilot Study

Background Cardiac gallium 68-labeled fibroblast activation protein inhibitor (FAPI)-4 (⁶⁸Ga-FAPI-4) PET/MRI allows simultaneous assessment of cardiac tissue characteristics, function, and molecular remodeling in myocardial diseases. An integrated workflow for nonischemic dilated cardiomyopathy (DCM) has yet to be developed. Purpose To evaluate the feasibility and performance of a time-efficient cardiac ⁶⁸Ga-FAPI-4 PET/MRI protocol in participants with DCM. Materials and Methods In this prospective study, participants with DCM and healthy controls were enrolled for hybrid ⁶⁸Ga-FAPI-4 PET/MRI. Additionally, comparison was made with a further control group of oncology patients without cardiovascular disease who underwent ⁶⁸Ga-FAPI-4 PET/CT. A 3.0-T PET/MRI system was used, enabling coregistered FAPI PET and cardiac MRI, including cine imaging, T1 and T2 mapping, and late gadolinium enhancement (LGE). Myocardial FAPI uptake was quantified, and correlations with cardiac MRI and clinical markers were assessed. Receiver operating characteristic analysis was used to evaluate the diagnostic performance of FAPI PET metrics for distinguishing participants with DCM from controls. Results This study included 37 participants (median age, 53 years [IQR, 48-58 years]; 32 male and five female). All participants completed a hybrid PET/MRI protocol, with mean cardiac MRI scan acquisition time and scanner room time of 32.0 minutes ± 6.0 (SD) and 37.6 minutes ± 6.6, respectively. Of the participants with DCM, 68% (17 of 25) showed elevated myocardial FAPI uptake, exceeding LGE extent in 73% of LGE- and FAPI-positive cases (eight of 11). In contrast, myocardial FAPI uptake was absent in healthy controls and oncology participants. Excellent diagnostic performance for DCM was observed for FAPI PET mean standardized uptake value (area under the receiver operating characteristic curve [AUC], 0.92 [95% CI: 0.82, 0.99]), maximum standardized uptake value (SUV_max) (AUC, 0.91 [95% CI: 0.81, 0.98]), and target to background ratio (AUC, 0.83 [95% CI: 0.69, 0.94]). SUV_max showed a positive correlation with left ventricular (LV) end-diastolic volume index (R = 0.47; P = .02) and a negative correlation with LV ejection fraction (R = -0.47; P = .02). SUV_max was positively correlated with T1 and T2 values (R = 0.21 and 0.30, respectively) and extracellular volume (R = 0.36) (all P < .001). Conclusion Hybrid cardiac ⁶⁸Ga-FAPI-4 PET/MRI successfully enabled simultaneous molecular and structural imaging for nonischemic DCM. Clinical trial registration no. ChiCTR1800017058 © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Kusmirek and Johnson in this issue.