Imaging the lymphatic system

Abstract

Visualization of the lymphatic system is clinically necessary during diagnosis or treatment of many conditions and diseases; it is used for identifying and monitoring lymphedema, for detecting metastatic lesions during cancer staging and for locating lymphatic structures so they can be spared during surgical procedures. Imaging lymphatic anatomy and function also plays an important role in experimental studies of lymphatic development and function, where spatial resolution and accessibility are better. Here, we review technologies for visualizing and imaging the lymphatic system for clinical applications. We then describe the use of lymphatic imaging in experimental systems as well as some of the emerging technologies for improving these methodologies.

Keywords: Clinical; Fluorescence; Imaging; Lymph node; Lymphatic function; Lymphatic metastasis; Lymphatic vessels; Lymphography; Models; Technologies.

Fig. 1

Imaging lymphatic vessels and lymph nodes in the clinic. (A) Lymphogram of a patient with lymphovenous shunt after surgery for right-sided inguinocrural hernia showing lack of lymph flow in the inguinocrural region (arrowheads) (Guermazi et al., 2003, reproduced with permission). (B) Lymphoscintigraphy of bilateral limb swelling. Lymph rerouting through the skin of right lower limb (solid arrowhead) and the deep lymphatics is apparent. Several popliteal nodes (open arrowhead) are visible. The left limb appears normal in this lymphoscintigraph (Burnand et al., 2011, reproduced with permission). (C) Coronal 3D MR lymphography image of the lower extremities obtained after subcutaneous injection of contrast material. Abnormal, dilated lymphatic vessels extend from the left calf to the inner thigh (small arrows). Some lymphatic vessels in the contralateral normal limb appear discontinuous (small arrows). Veins appear as linear structures with lower intensity (large arrows) (Lu et al., 2012). (D–F) PET-CT after radical prostatectomy. CT images are in (D), PET images 60 min after the administration of ¹⁸F-choline are in (E) and merged PET-CT images are in (F). The high intensity spot in the PET scan is a small right inguinal lymph node with likely metastasis (F: transverse plane; L: saggital plane; A: coronal plane) (Fortuin et al., 2013). (G–J) Near infrared imaging of healthy lymphatics in normal subjects. Lymphatic vessels in (G) hand, (H) arm, (I) foot, ankle, and leg, and (J) lower legs. Black spots are covered injection sites (Rasmussen et al., 2009, reproduced with permission).

Fig. 2

Lymphatic imaging in animal models. (A–C) Confocal microscopy of lymphatic development in the zebrafish. GFP signal comes from vessels in the Fli1:eGFPy1 embryo. Yellow arrowheads indicate normal thoracic duct in control embryos (A), which is absent in Dll4KD (B) and Notch-1bKD (C) embryos (Geudens et al., 2010, reproduced with permission). (D and E) Lymphatic vessels in a mouse tail imaged by fluorescence microscopy of FITC-dextran injected at the tip of the tail. Normal vasculature (D) is disrupted when a sarcoma is grown in the tail (E) (Leu et al., 2000, reproduced with permission). (F–H) Contraction of a collecting lymphatic vessel afferent to the popliteal lymph node in a mouse. A single pumping cycle lasting ~1.3 s is shown. The vessel was visualized by fluorescence microscopy of FITC-dextran injected in the footpad (Liao et al., 2011, reproduced with permission). (I and J) Lymphatic valve structures imaged using multiphoton microscopy identifies normal (I) and abnormal valves (J). Valve abnormalities are common around tumors (Hoshida et al., 2006). (K and L) Visualization of lymph flow redirection due to tumor growth in the hindlimb of a mouse using NIR imaging. (K) Normal uptake by collecting vessels and collateral flow (arrows). (L) Flow redirected through collecting vessel network (yellow arrows) toward the inguinal lymph node. Scale bar: 2 mm (Proulx et al., 2013a, reproduced with permission).

Fig. 3

Emerging technologies for lymphatic imaging. (A–C) Optical frequency domain imaging of blood and lymphatic vessels. Lymphatic vessels appear as dark features with resolution comparable to traditional optical microscopy, but no contrast agent is required; thus, more vessels are detected by OFDI (A) than traditional lymphangiography (B). Blood vessels (yellow) and lymphatic vessels (blue) can be visualized in the same tissue with appropriate processing (C) (Vakoc et al., 2009). (D–G) Wound healing visualized by OCT imaging. Lymphatic vessels (green) and blood vessels at day 1 (D), day 8 (E), day 15 (F) and day 22 (G) after excision with a biopsy punch. (Yousefi et al., 2013, reproduced with permission).