INVIVO AND INVITRO STUDY OF THE LESIONS PRODUCED WITH A COMPUTERIZED RADIOFREQUENCY SYSTEM

For many years, radiofrequency-generated lesions have been used for the treatment of pain and abnormal movements. However, the reliability of this method has been questioned because of the variation in the size of lesions produced by the electrode at different times and temperatures. A 500-kHz radiofrequency generator with different electrodes was used to determine the size of lesions, using different time and temperature exposures. A computerized feedback mechanism kept the tip temperature constant during the production of the lesion, regardless of varying tissue impedance. Eight electrodes of different size and tip characteristics were evaluated at different temperatures and time settings, both in vitro and in vivo. Graphic display of the curves in time were obtained at 65, 70, 75, 80, 85 and 90-degrees-C. The effects of thermocoagulation were studied in vitro in fresh egg whites, using time intervals of 20, 40, 60, 80 and 100 s, and in vivo, in the subcortical white matter of 20 adult New Zealand white rabbits. Animals were sacrificed after 7 days. Lesions were photographed and measured under magnification. In all cases, the coagulated masses were ellipsoid, with regular, well-demarcated borders. A two-way statistical analysis of variance was done. The coagulum size increased with higher temperatures and with larger probes. The increase was significant in both diameter and length (p = 0.001). In contrast, the use of different times at the same level of temperature showed no significant increase in most of the electrodes. There were two statistical significant time effects, for both diameter and length, with the monopolar 2-mm electrode. The use of real-time monitoring with graphic display and the feedback information provided for the computerized control of power and current allows high precision of the temperature at the electrode tip during the production of the lesion.