First experience imaging short-wave infrared fluorescence in a large animal: indocyanine green angiography of a pig brain.

The potential to image subsurface fluorescent contrast agents at high spatial resolution has facilitated growing interest in short-wave infrared (SWIR) imaging for biomedical applications. The early but growing literature showing improvements in resolution in small animal models suggests this is indeed the case, yet to date, images from larger animal models that more closely recapitulate humans have not been reported. We report the first imaging of SWIR fluorescence in a large animal model. Specifically, we imaged the vascular kinetics of an indocyanine green (ICG) bolus injection during open craniotomy of a mini-pig using a custom SWIR imaging instrument and a clinical-grade surgical microscope that images ICG in the near-infrared-I (NIR-I) window. Fluorescence images in the SWIR were observed to have higher spatial and contrast resolutions throughout the dynamic sequence, particularly in the smallest vessels. Additionally, vessels beneath a surface pool of blood were readily visualized in the SWIR images yet were obscured in the NIR-I channel. These first-in-large-animal observations represent an important translational step and suggest that SWIR imaging may provide higher spatial and contrast resolution images that are robust to the influence of blood.