A new device for inducing deep localized vaporization in liver with the Nd-YAG laser

A new device, composed of a hand-piece (250 mm in length, and 5 mm in diameter) connected to a cooling circulation, has been developed for the purpose of inducing focal coagulation deep in the liver, using a high-power Nd-YAG laser. The device, guiding and protecting the optical fibre, withstands a power-setting of 100 W and allows means transmission of 80% during intrahepatic application with an average power density of 10 200 W/cm2. Thirty-six lesions of 12–18 mm in diameter were made in 11 pigs under ultrasound control with laser shorts of 80 W mean power output for 10s duration. Intrahepatic thermocouples showed a high rise in temperature in the core of the lesion, inducing vaporization, while moderate hyperthermia (54.4%C/60s on average), high enough for tumour cell kill, was observed 1 cm from the laser source. Immediately after irradiation ultrasound revealed a central echo-free lesion, well defined on day 3 by a hyperechoic border and invaded from day 20 by internal hyperechoic enhancement. Anatomical examination demonstrated, on day 0, an excavated site of vaporization which was surround, from day 3 on wards, by an increasing ring of connective tissue, and which was covered, from day 30 onwards, by a fibrotic network gaining ground towards the centre of the lesion. Good healing free of complications, was observed after four months' follow-up. The technique is proposed for photocoagulation of deep metastases.