Background <p>[¹⁸F]AlF-FAPI-74 is a fibroblast activation protein inhibitor labeled with ¹⁸F. However, [¹⁸F]AlF-FAPI-74 PET displays bile excretion, which may be a interfering factor in interpreting images of pancreatic and biliary related cancers. The aim of this study is to evaluate the differences in physiological uptake of [¹⁸F]AlF-FAPI-74 and [⁶⁸Ga]Ga-FAPI-04 in the biliary system, as well as the biliary excretion pattern of [¹⁸F]AlF-FAPI-74, and to investigate how to eliminate this high physiological uptake in the biliary system.</p> Patients and methods <p>This prospective study recruited 20 patients who underwent [¹⁸F]AlF-FAPI-74 PET/CT and 10 patients who underwent [⁶⁸Ga]Ga-FAPI-04 PET/CT examination. Compare the PET parameters of five key anatomical sections and two image acquisition time points in the biliary system among different groups of patients, including SUV_max, SUV_mean, and tumor to background ratio (TBR) from intrahepatic bile duct to duodenum, using Mann Whitney U test.</p> Results <p>Compared with [⁶⁸Ga]Ga-FAPI-04, [¹⁸F]AlF-FAPI-74 demonstrated significantly higher physiological uptake in the hepatobiliary system (SUV_max/SUV_mean/TBR: all <i>P</i> &lt; 0.001). In the ¹⁸F-FAPI group, comparison between 120&#xa0;min and 60&#xa0;min post-injection revealed a statistically significant decrease only in intrahepatic bile duct uptake (SUV_max/SUV_mean/TBR: all <i>P</i> &lt; 0.05), indicating that [¹⁸F]AlF-FAPI-74 persisted in bile retention. The fatty meal intervention in the ¹⁸F-FAPI (FM) group effectively reduced biliary radioactivity to levels comparable to [⁶⁸Ga]Ga-FAPI-04 (TBR: <i>P</i> &gt; 0.05).</p> Conclusions <p>[¹⁸F]AlF-FAPI-74 exhibits significant and sustained physiological uptake in the biliary system, which may limit its assessment of biliary pancreatic cancer. Instructing patients to consume a fatty meal before imaging can effectively eliminate this intake and achieve a background level comparable to [⁶⁸Ga]Ga-FAPI-04.</p>