Mechanism of dynamic near-infrared fluorescence cholangiography of extrahepatic bile ducts and applications in detecting bile duct injuries using indocyanine green in animal models

Fluorescence intraoperative cholangiography (IOC) is a potential alternative for identifying anatomical variation and preventing iatrogenic bile duct injuries by using the near-infrared probe indocyanine green (ICG). However, the dynamic process and mechanism of fluorescence IOC have not been elucidated in previous publications. Herein, the optical properties of the complex of ICG and bile, dynamic fluorescence cholangiography and iatrogenic bile duct injuries were investigated. The emission spectrum of ICG in bile peaked at 844 nm and ICG had higher tissue penetration. Extrahepatic bile ducts could fluoresce 2 min after intravenous injection, and the fluorescence intensity reached a peak at 8 min. In addition, biliary dynamics were observed owing to ICG excretion from the bile ducts into the duodenum. Quantitative analysis indicated that ICG-guided fluorescence IOC possessed a high signal to noise ratio compared to the surrounding peripheral tissue and the portal vein. Fluorescence IOC was based on rapid uptake of circulating ICG in plasma by hepatic cells, excretion of ICG into the bile and then its interaction with protein molecules in the bile. Moreover, fluorescence IOC was sensitive to detect bile duct ligation and acute bile duct perforation using ICG in rat models. All of the results indicated that fluorescence IOC using ICG is a valid alternative for the cholangiography of extrahepatic bile ducts and has potential for measurement of biliary dynamics.