Indocyanine Green and Lymphatic Imaging: Current Problems

Background: Near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) has recently been presented as a comparatively easy and informative technique to image lymphatic channels in vivo. However, no data or references have been provided concerning the impact of ICG application on normal lymphatic contractility and lymph transport. Thus, the imaging agent and/or the method of administration may introduce a significant artifact. Methods and Results: Standard pharmacological tests were performed to investigate the influence of ICG on the spontaneous contractility of isolated, cannulated, and pressurized rat mesenteric lymphatic vessels. The data demonstrate that non-irradiated ICG dramatically and dynamically influences the contractility of rat lymphatic vessels in both a dose- and diluent-dependent manner with low ICG concentrations principally altering contractile frequency and higher ICG concentrations completely blocking lymphatic contractility. Conclusions: Currently, both researchers and doctors should exercise caution in extrapolating the data obtained with ICG imaging to normal lymphatic function regardless of whether it was obtained in mice, pigs, or humans. Careful and extended pharmacological tests must be performed to evaluate the mechanism of action of ICG on the contractility and physiology of lymphatic vessels with consideration of dose, diluent, and duration of irradiation.