Comparison of 18F-FAPI-42 PET for Detecting Cardiac Fibroblast Activation in Dilated Cardiomyopathy With Histopathology and CMR.

BACKGROUND

Myocardial fibrosis (MF) is a key pathophysiological characteristic of dilated cardiomyopathy (DCM). Radiolabeled imaging agents targeting fibroblast activation protein (FAP) enhance the accuracy and sensitivity for detecting early-stage myocardial fibrosis.

OBJECTIVES

This study aimed to evaluate the feasibility of using 18F-labeled FAP inhibitor tracer (FAPI-42) positron emission tomography (PET) imaging for detecting myocardial fibroblast activation and fibrosis in DCM patients.

METHODS

In total, 19 DCM patients underwent 18F-FAPI-42 PET/computed tomography imaging, with 14 also underwent cardiac PET/cardiac magnetic resonance (CMR). Four patients underwent cardiac transplantation within 9 to 124 days after PET scans. Control groups were enrolled to establish the normal range of 18F-FAPI activity and CMR parameters. Spearman correlation analysis assessed correlations between 18F-FAPI uptake, the degree of collagen fiber deposition and FAP fluorescence, cardiac function parameters obtained from echocardiography, and PET/CMR.

RESULTS

18F-FAPI PET imaging revealed varying degrees of FAPI uptake across diverse regions of the myocardium in DCM patients, significantly higher than the control group. 18F-FAPI-42 PET identified more abnormal segments (n = 168) than CMR-LGE (n = 95). Furthermore, in FAPI-positive segments, the T1-postcontrast values and extracellular volume % were higher than in FAPI-negative segments (n = 56). Additionally, the myocardial long-axis radial PS% capacity was more severely impaired. In heart transplant patients, the FAPI uptake strongly correlated with FAP mean fluorescence intensity (P < 0.001) and collagen fiber deposition (P < 0.05). The FAPI uptake also correlated with cardiac function parameters assessed by CMR (end-systolic volume, end-diastolic volume, left ventricular ejection fraction %, and extracellular volume %). As NYHA functional class progressed from Ⅱ to Ⅳ, metabolically active volume increased consistently. However, maximum standardized uptake value and total lesion FAPI initially increasing and then subsequently declining.

CONCLUSIONS

18F-FAPI PET is capable of detecting fibroblast activation in the myocardium of DCM, strongly correlating with histological markers and cardiac function parameters. Metabolically active volume is an effective indicator for assessing the condition of DCM, whereas maximum standardized uptake value and total lesion FAPI may potentially offer prognosis values.