Background: Whereas functional lymph imaging in rodents is imperative for drug discovery of lymph therapeutics, noninvasive imaging of propulsive lymph function in rodents has not been reported previously. Herein, we present a noninvasive and rapid approach to measure lymphatic function in a rodent model using a near-infrared (NIR) dye to minimize background autofluorescence and maximize tissue penetration.
Methods and results: Mice were dynamically imaged following intradermal (i.d.) injection of 2 to 10 microL of 1.3 mM of indocyanine green (IC-Green) into the tail and the limb. Our results demonstrate the ability to image the IC-Green trafficking from the lymph plexus, through lymph vessels and lymphangions, to the ischial nodes in the tail, and to the axillary nodes in the limb. Our results show that lymph flow velocity from the propelled IC-Green "packet" in the lymph vessels in the tail ranged from 1.3 to 3.9 mm/s and the fluorescence intensity peaks repeated on an average of every 51.3 +/- 17.4 seconds in five animals. While pulsatile lymph flow was detected in the deep lymph vessels, lymph propulsion was not visualized in the superficial lymphatic network in the tail. In axillary lymphatic imaging, propulsive lymph flow was also detected. The intensity profile shows that the lymph flow velocity ranged from 0.28 to 1.35 mm/s at a frequency ranging from 0.72 to 11.1 pulses per minute in five animals.
Conclusions: Our study demonstrates the ability to noninvasively and quantitatively image propulsive lymph flow, which could provide a new method to investigate lymph function and its change in response to potential therapeutics.