Macroscopic label-free biomedical imaging with shortwave infrared Raman scattering

Summary Shortwave infrared (SWIR) imaging provides enhanced tissue penetration and reduced autofluorescence in clinical and pre-clinical applications. However, existing applications often lack the ability to probe chemical composition and molecular specificity without the need for contrast agents. Here, we present a SWIR imaging approach that visualizes spontaneous Raman scattering with remarkable chemical contrast deep within tissue across large fields of view. Our results demonstrate that Raman scattering overcomes autofluorescence as the predominant source of endogenous tissue background at illumination wavelengths as short as 892 nm. We highlight the versatility of SWIR Raman imaging through in vivo monitoring of whole-body tissue composition dynamics and non-invasive detection of fatty liver disease in mice, and identification of calcification and lipids in unfixed human atherosclerotic plaques. Moreover, our approach facilitates the visualization of nerves embedded in fatty tissue, a major advancement for surgical applications. With a simple wide-field setup orthogonal to fluorescence, SWIR Raman imaging holds promise for rapid adoption by clinicians and biologists. This technique opens new possibilities for contrast agent-free visualization of pathophysiology in whole animals and intraoperative imaging in humans. Graphical abstract