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

Abstract

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.

Keywords: fluorescence-guided surgery; indocyanine green angiography; medical imaging; near-infrared-II window; short-wave infrared.

Fig. 1

(a) Relative time intervals between craniotomy and the two ICG injections for imaging ICG in the NIR-I and SWIR regimes. (b) Schematic diagram and (c) photograph of the SWIR imaging system used to collect SWIR fluorescence images during open pig craniotomy.

Fig. 2

(a) White-light image taken prior to ICG-bolus injections and (b)–(f) representative frames of the time-lapsed video showing the dynamic uptake of ICG bolus in pig brain using NIR-I (left) and SWIR (right) fluorescence from before injection to 5 min after administration (Video 1, MOV, 697 KB [URL: https://doi.org/10.1117/1.JBO.24.8.080501.1]).

Fig. 3

(a) Locations of profile lines numbered and shown overlaid on white-light, NIR-I, and SWIR images. (b)–(e) Corresponding NIR-I and SWIR intensity profile curves plotted as a function of position.

Fig. 4

(a–d) Dynamic VTR values plotted as a function of time with corresponding vessel and tissue ROIs outlined above each respective vessel-to-tissue contrast plot.