Simultaneous Near-Infrared Fluorescence Imaging of the Bile Duct and Hepatic Arterial Anatomy for Image-Guided Surgery

Abstract

Two independent wavelengths of a near-infrared (NIR) fluorescent light probe are currently available in the clinical setting. These enable us to simultaneously see two different anatomies and/or functions. Many reports are available showing that NIR fluorescence imaging and merged imaging of normal light and NIR light are useful for intraoperative image guidance. Dual-channel NIR fluorescence imaging has already been reported. It has potential to provide easy-to-understand, real-time, intraoperative imaging in more detail than single-channel NIR fluorescence imaging. Indocyanine green (ICG), of which the fluorescence wavelength is about 800 nm, and methylene blue (MB), of which the fluorescence wavelength is about 700 nm, can be used for the probe of NIR fluorescence imaging with the use of an appropriate NIR camera. The FLARE (Fluorescence-Assisted Resection and Exploration) system provides simultaneous dual-channel fluorescence imaging. The results of the initial preclinical trial of dual-channel NIR imaging for a cardiac application have been published as well as the simultaneous visualization of bile ducts and hepatic arteries in the preclinical setting. Both ICG and MB eliminate into bile after intravenous injection. The nonmetabolized elimination of both ICG and MB can detect fluorescence out of the bile. Intravenous injection of ICG, MB, and their combination can visualize the hepatic arteries and bile ducts in a different phase. MB has a lower extinction coefficient than ICG, i.e. ICG is a brighter fluorescence material than MB. However, ICG has poor liver-bile duct signal contrast because ICG accumulates in the liver rapidly and persistently. Furthermore, MB can visualize the bile duct more rapidly after intravenous injection than ICG because MB shows faster elimination into bile after intravenous injection. This technology has potential to provide appropriate intraoperative image guidance that can enable us to perform surgery more safely and precisely in a clinical situation.