Functional lymphatics are essential for removal and transport of cellular waste and excess fluid from regional tissues and are dependent upon contractile lymphangion activity for proximal drainage into the venous blood stream. Lymphatic insufficiency in patients with cancer-acquired lymphedema is manifested by progressive dermal backflow, or retrograde flow of lymph into dermal lymphatic capillaries. Prior studies using near-infrared fluorescence (NIRF) lymphatic imaging with ICG as a contrast agent, found that dermal backflow provides early indication of lymphedema onset which, when untreated, persists over months and years, but, with two weeks of physiotherapy, dermal backflow could be resolved or reduced in early head and neck cancer survivorship. Thus, the extent or area of dermal backflow may provide an accurate, longitudinal measure of progressing/improving lymphatic dysfunction. In this work, we develop hardware and software solutions to automate determination of dermal backflow area on 3-dimensional tissue surface profiles for entry into the medical record. Specifically, we incorporate a stereo depth module into our custom NIRF lymphatic imaging system for simultaneous acquisition of depth, color, and NIRF images. Using camera calibration techniques, NIRF images are mapped onto point clouds derived from depth images. Algorithms for image segmentation of dermal backflow and stitching of multiple point clouds for more complete representation of dermal backflow across complex 3-dimensional tissue surfaces are described. Non-clinical testing demonstrates ±3% errors in dermal backflow area determination, with clinical testing on head and neck cancer survivors underway to assess efficacy of physiotherapies provided early after cancer treatment.
KEYWORDS: Lymphatic system, Luminescence, Brain, Imaging systems, In vivo imaging, Near infrared, Medicine, Health sciences, Indocyanine green, Fluid dynamics
Cerebrospinal fluid (CSF) is known to be reabsorbed by the lymphatic vessels and drain into the lymph nodes (LNs) through peripheral lymphatic vessels. In the peripheral lymphatics, the contractile pumping action of lymphangions mediates lymph drainage; yet it is unknown whether lymphatic vessels draining cranial and spinal CSF show similar function. Herein, we used non-invasive near-infrared fluorescence imaging (NIRFI) to image (i) indocyanine green (ICG) distribution along the neuraxis and (ii) routes of ICG-laden CSF outflow into the lymphatics following intrathecal lumbar administration. For intrathecal injection, a 31-gauge needle was inserted between L5 and L6 vertebrae and a tail flick response was referenced as indication of correct position of the needle into the intradural space. Imaging agents were injected immediately after a tail flick. A volume of 10 to 30μl of 645μΜ of ICG was injected. We demonstrate lymphatic contractile function in peripheral lymphatics draining from the nasal lymphatics to the mandibular LNs. In addition, we observed afferent sciatic lymphatic vessels, which also show contractile activity and transport spinal CSF into the sciatic LNs. NIRFI could be used as a tool to probe CSF pathology including neurological disorders by imaging CSF outflow dynamics to lymphatics.
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