Comparison between near-infrared fluorescence imaging with indocyanine green and infrared imaging: on-bench trial for kidney perfusion analysis. A project of the ESUT-YAUWP group.

BACKGROUND: Infrared thermography (IRT) imaging technology is able to measure surface temperatures in real-time. The aim of our study is to understand whether IRT imaging is a reliable technology for the assessment of kidney-parenchyma perfusion with warm fluids.
METHODS: We used three porcine kidneys as a sample. IRT was compared to Near-infrared fluorescence (NIRF) technology with Indocyanine Green (ICG), X-rays with Contrast medium was used as a benchmark. Each kidney, placed inside an incubator, was perfused with contrast medium by a vascular 6-Fr catheter, to preview the perfusable parenchymal area. 100 mL of saline solution at 45 °C was then administered along a five-minutes time, followed by a second administration of 2/10 diluted ICG solution. A FLIR© C2 IR camera was used to acquire thermal data. During ICG administration, image acquisition was obtained with FireFly technology, with a 0° endoscopic camera. Quantitative variables are described using median and quartiles.
RESULTS: Real-time evaluation by IRT showed that, after five minutes of perfusion, it was possible to highlight the same parenchymal areas as visualized by X-ray. The IR images showed that surface temperature rise was directly reflecting local perfusion with heated saline solution. Analysis of NIRF technology and ICG showed an overlap between the two technologies. In addition to the compared technology, IR provided separate temperature measurement for each pixel in real time. Our findings were replicable on all the three kidneys examined. Higher resolution IR-cameras could provide even more detailed information.
CONCLUSIONS: Although NIRF technology with ICG is providing more image detail, we demonstrated that IRT is capable of detecting kidney parenchyma perfusion with warm fluids. Further studies will show its feasibility in graft re-perfusion assessment during kidney transplant or similar applications.