Semiquantitative analysis of 18F-aluminum fluoride fibroblast activation protein inhibitor 42 PET/computed tomography in primary liver cancer and factors influencing imaging positivity rates.

Objectives: This study evaluated 18F-aluminum fluoride fibroblast activation protein inhibitor 42 (18F-AlF-FAPI-42) PET/computed tomography (CT) imaging characteristics in primary liver cancer (PLC) and analyzed detection rate determinants.

Methods: Fifty-three untreated patients (76 lesions) with suspected PLC [hepatocellular carcinoma (HCC) or non-HCC subtypes] underwent 18F-AlF-FAPI-42 PET/CT. Maximum standardized uptake value (SUV max ) of lesions and mean SUV of adjacent normal liver tissue were measured to calculate target-to-background ratio (TBR). Patients were stratified by pathology, cirrhosis status, lesion size [small (3 cm), nodular (3-5 cm), massive (>5 cm)], lesion number, and alpha-fetoprotein (AFP).

Results: Overall positivity rate was 86.8% (66/76 lesions). Non-HCC lesions showed significantly higher SUV max (15.6 vs. 10.3; P < 0.001) and TBR (12.6 vs. 3.9; P < 0.001) than HCC. Lesion size correlated with SUV max ( r = 0.54) and TBR ( r = 0.37) (both P < 0.001). HCC demonstrated lower detection than non-HCC (80.6 vs. 100%; P = 0.018), while cirrhotic patients showed reduced detection vs. noncirrhotic (80 vs. 96.8%; P = 0.034). Detection rates increased with lesion size: 72.0% (small), 80.0% (nodular), and 100% (massive) ( P = 0.004). Lesion number and AFP levels showed no significant impact. Subgroup analysis confirmed lesion size and pathological type as independent predictors ( P < 0.05), while cirrhosis showed no independent effect ( P > 0.05).

Conclusion: 18F-AlF-FAPI-42 PET/CT demonstrates high sensitivity for PLC, particularly for non-HCC subtypes and larger lesions. While smaller HCCs show reduced detection, cirrhosis doesn't significantly impair diagnostic performance, supporting its clinical utility in cirrhotic populations.