This chapter delves into the PET/CT imaging technology, highlighting its integration of functional metabolic imaging from PET and anatomical structure imaging from CT. The technology involves injecting a radioactive tracer which usually is 18F-FDG, observing its distribution in the body, and using CT to pinpoint its location, combining the strengths of both imaging modalities for superior diagnostic insights. The section one explains the PET/CT scanner’s structure, including its data processing and image display systems, and discusses the importance of various corrections to raw data for accurate image reconstruction. The text emphasizes PET/CT’s high spatial resolution, sensitivity, and the ability to perform accurate tissue attenuation correction. It underscores the technology’s advantages, such as improved lesion localization, superior diagnostic accuracy over standalone PET or CT, and its value in guiding radiotherapy. The examination method varies, with the text noting the importance of preconditions like fasting and glucose control for hepatobiliary system imaging. The application of PET/CT in hepatobiliary diseases is described in section two, noting its utility in diagnosing liver tumors, differentiating benign from malignant lesions, staging tumors, evaluating treatment efficacy, and monitoring for recurrence. The text provides examples of how PET/CT imaging can assist in identifying primary liver cancer, metastases, and other liver lesions, including the challenges of differentiating physiological from pathological uptake. The chapter concludes by discussing the role of PET/CT in diagnosing cholangiocarcinoma and differentiating between benign and malignant liver lesions, emphasizing the need to combine PET/CT findings with other imaging results for accurate diagnosis. It also mentions the limitations of PET/CT in imaging very small malignant tumors in the bile duct and the importance of distinguishing infective liver lesions from tumors.