Low power interstitial Nd-YAG laser photocoagulation in normal rabbit brain

The safe, effective, clinical application of interstitial laser irradiation to destroy brain tumour tissue requires a knowledge of the relation of the extent of laser-induced (thermal) necrosis to the delivered laser power and total energy, and to time post-irradiation. We have conducted experiments to determine these relationships in normal rabbit brain. Irradiation by a Nd-YAG laser (1064 nm), at powers of 0.5–3.0 W and exposures of 200–1333 s produced well-defined necrotic lesions whose size increased with both the power and the total energy delivered. Lesions of 6 mm diameter made by 0.75 W for 1000s were well tolerated by animals allowed to recover from anaesthesia following irradiation. The diameter of the lesion was greatest at 48 h after irradiation. Following evolution of a characteristic healing response to necrosis in brain, the residual damage at 4 weeks was no greater in volume than that of the acute lesion. The results suggest that low power interstitial Nd-YAG laser photocoagulation in brain can be reliably and safely effected.