Concentration of Indocyanine Green Does Not Significantly Influence Lymphatic Function as Assessed by Near-Infrared Imaging

Background: Absorbance of near-infrared (600-800 nm) light by the tissue components water, melanin, and hemoglobin is minimal. This property allows the use of near-infrared-emitting fluorophores for noninvasive, in vivo, real-time imaging of tissue, without the interference of autofluorescence experienced with imaging in other wavelength ranges. Near-infrared (NIR) fluorescence imaging has been used to noninvasively image lymphatic architecture and pumping function in animals, as well as in humans. The effects of different doses of a NIR dye, indocyanine green (ICG), on lymphatic function have been questioned. This study aims to address these concerns in the context of a mouse inguinal-to-axillary lymphatic imaging model. Methods and Results: We measured lymph propulsive velocity and frequency using an imaging system composed of a laser diode for excitation of the dye, an image intensifier, and an intensified charge-coupled device (ICCD) camera to capture real-time images. At 0.32, 0.645, and 1.3 mM ICG, no significant differences in lymphatic propulsive velocity or frequency were observed. Additionally, the use of other NIR imaging agents did not result in significant differences. Conclusions: The use of different concentrations of ICG and the use of other near-infrared fluorophores for optical imaging of lymphatics does not significantly affect lymphatic propulsive velocity or frequency.