68Ga-FAPI PET/CT for molecular assessment of fibroblast activation in right heart in pulmonary arterial hypertension: a single-center, pilot study

Background Positron emission tomography (PET) imaging with radiolabeled fibroblasts activation protein inhibitor (FAPI) provides the opportunity to directly visualize fibrosis. This study aimed to investigate the feasibility of Ga-68-FAPI PET imaging in assessing right ventricular (RV) fibrotic remodeling and the relationship between FAPI uptake with parameters of pulmonary hemodynamics and cardiac function in pulmonary arterial hypertension (PAH) patients. Methods In this pilot study, sixteen PAH patients were enrolled to participate in cardiac Ga-68-FAPI PET/CT imaging. All patients underwent right heart catheterization and echocardiography for assessment of pulmonary hemodynamics and cardiac function within seven days. Cardiac FAPI uptake was visually assessed and quantified as maximum standardized uptake value (SUVmax). Results Twelve PAH patients exhibited FAPI uptake in RV free wall and insertion point. The overall activity of FAPI accumulated in the RV free wall (SUVmax: 2.5 +/- 1.8, P < 0.001) and insertion point (SUVmax:2.5 +/- 1.7, P < 0.001) was significantly upregulated compared to left ventricle (SUVmax:1.5 +/- 0.5). Patients with tricuspid annular plane systolic excursion (TAPSE) < 17 mm presented significantly higher uptake than those with TAPSE >= 17 mm in both RV free wall (SUVmax: 3.4 +/- 1.9 vs 1.7 +/- 1.1, P = 0.010) and insertion point (SUVmax: 3.4 +/- 1.9 vs 1.6 +/- 0.7, P = 0.028), indicating RV uptake of FAPI was associated with RV dysfunction. There was significant positive correlation between cardiac FAPI uptake and total pulmonary resistance and the level of N-terminal pro b-type natriuretic peptide. Conclusions Ga-68-FAPI PET/CT imaging is feasible to directly visualize fibrotic remodeling of RV in patients with PAH.