Figure 1.

Lymphatic imaging and flow measurement using Doppler OCT. (a) Anatomy of initial and collecting lymphatic vessels and valve function. Initial lymphatic vessels on the left collect interstitial fluid to create lymph, which is carried to a lymph node by a collecting lymphatic vessel. Lymphatic muscle cells can contract to drive flow, while intraluminal valves can close to prevent net backflow. The vessel segment between two valves is called a lymphangion. The figure is adapted with permission from Padera et al. [1]. (b) Schematic of the imaging setup. The light path is displayed in red. A portion of the collimated light is reflected to a mirror providing a reference signal for phase instabilities correction. A 2-axis galvanometer-based optical scanner is used to steer the beam. The beam shift (Δy) provides the Doppler angle α. The mouse is positioned with the lymphatic vessel along the y axis on a tilted platform with an angle of 15 degrees to provide a gravity induced opposing pressure gradient to lymph flow. The optical system has similar tilt to the tilted platform. (c) A cross-sectional image along the lymphatic vessel extracted from the volume data and used to calculate the Doppler angle at each flow location. Arrowheads point to intraluminal valves. Dashed region shows a close-up of a valve. Depending on their angular orientation within the vessel, the valves are better visualized in the cross-section or in the en face plane (Fig. 4b). Scale bars denote 130 μm.