¹⁸F-FAPI-42 PET/MR for the Evaluation of Small (≤3 cm) Hepatic Lesions: A Preliminary Study

To evaluate the diagnostic performance of ¹⁸F-fibroblast activation protein inhibitor (FAPI)-42 PET/MR for small (≤3 cm) hepatic lesions and to compare it with MRI and ¹⁸F-fluorodeoxyglucose (FDG) PET/MR.

This prospective study enrolled patients with suspected hepatic malignancies who underwent both ¹⁸F-FDG and ¹⁸F-FAPI-42 PET/MR. The maximum standardized uptake value (SUVmax) and tumor-to-background ratio (TBR) were recorded. Using histopathology or radiologic follow-up as reference standard, diagnostic performance was compared across imaging sets stratified by lesion size.

Twenty-five patients (17 males; median age 57.2 years) with 96 lesions were enrolled. SUVmax was comparable between ¹⁸F-FAPI-42 and ¹⁸F-FDG (5.08 ± 0.50 vs. 5.58 ± 0.39, P > 0.05), whereas TBR was significantly higher for ¹⁸F-FAPI-42 (6.90 ± 0.49 vs. 2.43 ± 0.16, P < 0.001). Lesion-based analysis showed that ¹⁸F-FAPI-42 PET exhibited higher sensitivity (97.6% vs. 72.9%, P = 0.023) and accuracy (96.9% vs. 75.0%, P = 0.021) than ¹⁸F-FDG PET, particularly for lesions ≤1 cm (96.6% vs. 66.1%, P = 0.038; 96.8% vs. 68.3%, P = 0.042). MRI showed lower diagnostic performance, while ¹⁸F-FAPI-42 PET, ¹⁸F-FDG PET/MR and ¹⁸F-FAPI-42 PET/MR all demonstrated superior sensitivity and accuracy, especially for lesions ≤1 cm (P < 0.05, all). In addition, ¹⁸F-FAPI-42 PET/MR altered clinical management in 20.0% of patients.

¹⁸F-FAPI-42 PET/MR improved diagnostic sensitivity and accuracy for small hepatic lesions with predominant metastatic involvement, particularly those ≤1 cm. ¹⁸F-FAPI-42 PET/MR may represent a promising one-stop solution for small hepatic lesions.