Feasibility of 68Ga-Labeled Fibroblast Activation Protein Inhibitor PET/CT in Light-Chain Cardiac Amyloidosis

Systemic amyloid light chain (AL) amyloidosis is the most common type of amyloidosis, leading to cardiomyocyte necrosis and interstitial fibrosis. Gallium-68-labeled fibroblast activation protein inhibitor 04 (68Ga-FAPI-04) has recently been introduced for imaging fibroblast activation in cardiac diseases. To date, cardiac fibroblast and cardiac amyloidosis (CA) phenotype activities have not been mapped.The aim of this study was to evaluate the feasibility of 68Ga-FAPI-04 positron emission tomography (PET)/computed tomography (CT) in assessing AL CA.Thirty consecutive patients (mean age: 59.1 ± 7.7 years; 20 men, 10 women) with biopsy-proven AL amyloidosis were enrolled prospectively (including 27 with AL CA and 3 without AL CA). All patients underwent 68Ga-FAPI-04 PET/CT (107.4 ± 26.5 MBq). Global standardized uptake values and left ventricular (LV) molecular volume were calculated in correlation to echocardiography (n = 30), cardiac magnetic resonance (n = 18), and clinical biomarkers. Subsequently, the patients were categorized as having patchy (PET-patchy), extensive (PET-extensive), and negative (PET-negative) patterns.Of all patients, 80% (24 of 30) showed increased LV uptake (PET-patchy [n = 4] vs PET-extensive [n = 20]), whereas 6 patients did not show visible myocardial uptake. Standardized uptake value ratio and LV molecular volume were significantly higher in the PET-extensive than the PET-patchy group (2.79 mL ± 1.22 mL vs 1.53 mL ± 0.66 mL [P = 0.045] and 198.3 mL ± 59.97 mL vs 127.8 mL ± 25.82 [P = 0.005], respectively). Additionally, 68Ga-FAPI-04 uptake was significantly correlated with clinical biomarkers (Mayo stage and N-terminal pro-brain natriuretic peptide), interventricular septal thickness, left ventricular ejection fraction (LVEF), LV end-systolic volume, extracellular volume, and LV global strain (P < 0.05).68Ga-FAPI-04 PET/CT is feasible in detecting myocardial fibroblast activation in patients with AL CA in correlation with myocardial remodeling. It might provide complementary information on cardiac molecular characterization and staging of disease.