Macroscopic label-free biomedical imaging with shortwave infrared Raman scattering
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Abstract
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.
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fields of view surpassing 50 cm2
This is indeed an impressive field of view, and the apparent SNR is impressive for ~10s exposures. More details on the laser power, diffuser, and detection optics would be appreciated!
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Pixel intensity profile along a line crossing the xiphoid cartilage on the mouse chest
Could you annotate the reference line in the plot to make it more clear where the pixel intensities in (c) are extracted from.
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we acquired SWIR Raman images from intact mice illuminated from 785 nm, a commonly used wavelength in Raman imaging, to 1064 nm, a red-shifted wavelength that extends Raman scattering wavelengths beyond the limits of standard InGaAs-based detectors
Could you provide information on the laser you used for this? It would be great if you could provide a more complete description of your experimental setup in a Methods section.
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the only necessary image processing being dark current correction
It's surprising to me that dark current poses more of a problem than autofluorescence. I'm curious if the dark current is somehow exacerbated when detecting in the SWIR region or if it would be mitigated simply with better detector cooling?
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