Real time imaging and quantitative evaluation of the emphysematous lung by infrared thoracoscopy in experimental dogs

To accurately excise emphysematous lung tissue in volume reduction surgery, we projected a digitally analyzed excision line on the real time image obtained by infrared thoracoscopy (IRT) with indocyanine green (ICG) intravenous injection. Emphysema was created in the canine lung by intrabronchial injection of elastase. We examined the emphysematous lung by IRT after intravenous injection of ICG. A digitized static image was obtained and analyzed in real time during the surgery. The color densities on the image were measured and the color density ratios (CDRs) calculated. We resected lung areas where the CDR was 1.0 or less. Resected and residual lung areas were examined microscopically. Microscopically, areas displayed as white by IRT with intravenous injection of ICG were emphysematous, and areas displayed as blue were normal. Areas with a CDR of 1.0 or less were emphysematous, and we were able to determine an appropriate excision line by connecting sample points with a CDR of 1.0. Use of digital image analysis combined with IRT after ICG injection enabled us to remove emphysematous regions accurately.