Total-Body 18 F-FAPI PET/CT for Assessment of Metabolic Dysfunction–Associated Steatotic Liver Disease: A Pilot Study

Liver biopsy remains the gold standard for fibrosis assessment; however, its invasiveness limits its suitability for routine clinical use. The rising prevalence of metabolic dysfunction–associated steatotic liver disease (MASLD) as a leading cause of chronic liver disease and hepatocellular carcinoma underscores the need for reliable noninvasive assessment. Current noninvasive imaging methods provide surrogate measures of fibrosis but do not directly assess fibrogenic activity. In contrast, fibroblast activation protein inhibitor (FAPI) PET enables molecular imaging of activated fibroblasts, a key driver of fibrosis. This study evaluates dynamic 18F-FAPI-74 PET imaging to assess hepatic fibrogenic activity in MASLD. Methods: In this prospective pilot study, 10 subjects (3 healthy volunteers, 4 patients with mild–moderate fibrosis, and 3 patients with advanced fibrosis) underwent 60-min dynamic 18F-FAPI-74 PET/CT. SUV and blood-normalized SUV ratio (SUVR) were quantified across time frames, and the net influx rate was derived from dynamic data. MR elastography–derived liver stiffness values were obtained for comparison. Correlations with histologic fibrosis scoring of biopsy tissue were assessed using Spearman analysis. Results: At 5 min postinjection, SUVR correlated strongly with histologic fibrosis score (ρ = 0.95; 95% CI, 0.75–1.00; P = 1.89 × 10−5), followed by SUV (ρ = 0.78; 95% CI, 0.23–0.98; P = 0.0077) and net influx rate from kinetic modeling (ρ = 0.84; 95% CI, 0.41–0.98; P = 0.0022). SUVR at the 4- to 5-min interval allowed clearer differentiation among healthy volunteers, patients with mild fibrosis, and patients with advanced fibrosis. Conclusion: Dynamic 18F-FAPI-74 PET enables quantitative visualization of hepatic fibroblast activation in MASLD. SUVR at the 4- to 5-min interval correlates more strongly with fibrosis severity, supporting 18F-FAPI-74 PET as a promising molecular biomarker for assessing and potentially monitoring metabolic fibrosis.