The lymphatic system, the body's second largest circulatory network, plays a crucial role in maintaining fluid balance and immune function. Despite its importance, studying lymphatic vessel function has been challenging due to limited imaging techniques.
One of the main challenges in studying the lymphatic system is the high variability in the structure and arrangement of its vessels. Unlike blood vessels, lymphatic vessels do not have consistent locations and branching patterns, making them hard to locate and analyze. Their small size adds to the difficulty. Previous imaging methods like X-ray, fluorescence lymphangiography, lymphoscintigraphy, and photoacoustic imaging can show the structure and function of lymphatic vessels but struggle to measure lymph transport accurately over time. Recent advancements in shortwave-infrared (SWIR) imaging offer a promising solution, providing clearer and more detailed images of lymphatic circulation compared to traditional near-infrared (NIR) imaging.
As reported in Journal of Biomedical Optics (JBO), researchers recently used SWIR fluorescence imaging to investigate the structure and function of lymphatic vessels in vivo. By comparing two imaging modalities-;near-infrared first window (NIR-I, 700 to 900 nm) and SWIR (900 to 1800 nm)-;and two fluorescent probes-;indocyanine green (ICG) and silver sulfide quantum dots (QDs)-;they aimed to determine the effectiveness of SWIR imaging in providing detailed lymphatic images in an animal model.
The results demonstrated that SWIR imaging significantly reduces scattering and autofluorescence background, resulting in clearer images. Specifically, SWIR imaging with ICG offered 1.7 times better resolution and sensitivity than NIR-I, while SWIR imaging with QDs nearly doubled the resolution and sensitivity, enhancing the distinguishability of lymphatic vessels. This improvement allows for more accurate estimation of vessel size in vivo compared to conventional NIR-I imaging.
The study concluded that SWIR imaging, particularly with silver sulfide QDs, provides superior image resolution, outperforming traditional NIR-I imaging techniques. This advancement in imaging technology holds great potential for improving our understanding of the lymphatic system and its functions.
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