[Experimental analysis of in-depth temperature distribution in echo-guided in-depth irradiation with YAG laser]

In the echo-guided in-depth irradiation using YAG laser, liver cancer is spherically coagulated by the heat effect of YAG laser. To analyse the temperature distribution in the excised bovine and canine livers, the thermometric system was devised. The temperature distribution on the plane of laser fiber was displayed with isothermal lines drawn every 10 degrees C. Vaporized cavity, charcoal zone, and coagulated zone were formed in this order around the laser fiber tip. In charcoal zone, nuclei were pyknotic or disappeared, and cytoplasm became densely eosinophilic. In coagulated zone, hepatocytes were atrophic and degenerated. At the charcoal zone, the temperature was about 200 degrees C and at the outer margin of the coagulated zone, it was about 60 degrees C. Coagulated zone corresponded to the hyperechoic area on echogram. Tissue change was always greater than the hyperechoic area by 2 to 3 mm. Near the laser fiber tip, tissue was vaporized to generate very hot gas. This gas spread along the Glisson's sheath and caused degeneration of vessels and bile ducts. In order to prevent this side effect, gas evacuation system was devised. It was histologically ascertained that this system worked effectively for this purpose. Blood flow carried away heat energy during laser irradiation. In-depth temperature rose more rapidly by Pringle's maneuver. It was speculated Pringle's maneuver could shorten the irradiation time of YAG laser.