Experimental radiofrequency (RF) coagulation with computer-based on line monitoring of temperature and power

The safety and reliability of radiofrequency coagulative techniques are questioned after each coagulation, especially in functional neurosurgery. In spite of the high level of technical development of modern surgical RF generators there is still uncertainty about the character of the coagulative lesion. For the present study, a 500 kHz RF generator was connected through a module for analog/digital conversion and for regulation to a personal computer provided with a software programme for the graphic display in real time of the RF power and of the temperature/time curves. The effects of thermocoagulation were studied in fresh egg white, and monopolar lesions were made in the subcortical white matter of rabbits with a probe with a 0.5 mm diameter and a bare tip of 3 mm in length. The regularity of thermocoagulation depends on the accurate temperature reading at the tip of the electrode. The ideal course of the temperature is a smoothly ascending curve from the level of 37 degrees C to the level present for coagulation, followed by a straight horizontal line. With too slow a response of the probe to temperature changes there is an inherent danger of overheating in the initial phase of the procedure. Additionally the power level has to be adjusted for each probe. On line monitoring with graphic display of the physical parameters provides a direct control of the course of the coagulation. Regular curves of the physical parameters without temperature overshoot correspond to reproducible lesions in vitro and in vivo.