Comparisons of Quantitative Parameters of Ga-68-Labelled Fibroblast Activating Protein Inhibitor (FAPI) PET/CT and [ 18 F]F-FDG PET/CT in Patients with Liver Malignancies

Purpose To compare quantitative parameters and tumour detection rates of [ 68 Ga]Ga-FAPI PET/CT with those of dedicated liver PET/MRI and 18 F-FDG PET in patients with liver malignancies. Procedures Twenty-seven patients (29 imaging studies) with diagnosed or suspected liver malignancies who underwent [ 68 Ga]Ga-FAPI-46 PET/CT, liver PET/MRI, and [ 18 F]FDG PET/CT between September 2020 and June 2021 were retrospectively analysed. MRI findings were used as the reference standard for diagnosis. Results The 27 patients had a median age of 68 years (interquartile range: 60–74 years; 21 men). Primary intrahepatic tumours were reported in 13 patients (15 imaging studies) with cholangiocarcinoma (CCA) and in 14 patients with hepatocellular carcinoma (HCC). All intrahepatic lesions detectable on MRI were also detected on [ 68 Ga]Ga-FAPI-46 PET/CT giving a sensitivity of 100% (19/19), whereas the sensitivity of [ 18 F]FDG PET/CT was 58% (11/19). All intrahepatic lesions were detected on [ 68 Ga]Ga-FAPI-46 PET/CT, on which they showed higher activity (median SUVmax: 15.61 vs. 5.17; P < .001) and higher target-to-background ratio (TBR; median, 15.90 vs. 1.69, P < .001) than on [ 18 F]FDG, especially in patients with CCA (median TBR, 21.08 vs. 1.47, respectively; P < .001). The uptake positivity rate in regional node metastasis was 100% (12/12) on [ 68 Ga]Ga-FAPI-46 PET/CT compared with 58% (7/12) on [ 18 F]FDG PET/CT. All patients with distant metastasis (100%, 14/14) were detected on both [ 18 F]FDG and [ 68 Ga]Ga-FAPI-46 PET/CT imaging, although more distant metastatic lesions were detected on [ 68 Ga]Ga-FAPI-46 PET/CT than on [ 18 F]FDG (96% (42/44) vs. 89% (39/44), respectively). Conclusion [ 68 Ga]Ga-FAPI PET/CT with dedicated liver PET/MRI shows potential for superior detection of hepatic malignancy compared with [ 18 F]FDG PET/CT or MRI alone.