Imaging the Deep Spinal Cord Microvascular Structure and Function with High-Speed NIR-II Fluorescence Microscopy

The spinal cord (SC) is crucial for a myriad of somatosensory, autonomic signal processing, and transductions. Understanding the SC vascular structure and function thus plays an integral part in neuroscience and clinical research. However, the dense layers of myelinated ascending axons on the dorsal side inconveniently grant the SC tissue with high optical scattering property, which significantly hinders the imaging depth of the SC vasculature in vivo. Commonly used antiscattering techniques such as multiphoton fluorescence microscopy have low imaging speed and cannot capture the rapid vascular particle flow without significant motion blur. Here, advantage of the high penetration of near-infrared (NIR)-II fluorescence is taken to demonstrate a deep SC vascular structural image stack up to 350 mu m, comparable to twophoton microscopy. Furthermore, the red blood cells are labelled with the clinically approved NIR dye indocyanine. The combination of a fast N IR camera and indocyanine green-red blood cells (RBCs) makes it possible to attain high-speed 100 frame-per-second NIR-II imaging to identify the corresponding changes in RBC velocity during the external hind leg stimulus. For the first time, it is established that the NIR-II region would be a promising spectral window for SC imaging. NIR-II fluorescence microscopy has excellent potential for clinical and basic science research on SC.

Automated summary

The spinal cord plays a crucial role in somatosensory and autonomic signal processing. However, the high optical scattering property of the spinal cord tissue hinders the imaging depth of its vasculature. In this study, the high penetration of near-infrared fluorescence is used to achieve deep imaging of the spinal cord vasculature. This technique has the potential for clinical and basic science research on the spinal cord.