Measurements of lymph flow

Abstract

The lymphatic vasculature is present in nearly every tissue of the body to serve essential functions in fluid homeostasis, immune cell trafficking, and lipid transport, and it has been implicated in the progression of several diseases. This is achieved through the intrinsic contractility of the pumping collecting lymphatics returning fluid up a pressure gradient from the interstitium to the venous circulation. Despite the critical roles that this system performs, very little is known about the lymphatic vasculature in comparison to the blood vasculature, which can be attributed, in part, to the difficulty associated with imaging lymphatic vessels. With the growing interest in studying lymphatic vessels, new techniques are being developed to improve the spatial resolution to visualize small initial lymphatics and increase temporal resolution to capture the dynamic lymphatic pump function responsible for fluid propulsion. In this chapter, we summarize imaging techniques currently used to study lymphatics in vivo, including the two gold standards of lymphatic imaging, lymphoscintigraphy and MRI, as well as PET and CT scanning, ultrasound, and optical imaging techniques. We detail the advantages and limitations of each technique in the context of visualizing lymphatic vessel geometries, quantifying dynamic lymph transport, and identifying sentinel lymph nodes. We also discuss emerging imaging technologies as potential techniques for the future of lymphatic imaging.