Interstitial electrolyte infusion creates a liquid electrode for controlled application of high power radiofrequency energy

Conventional techniques of applying radiofrequency (RF) energy for thermotherapeutic purposes is limited by small lesion size, tissue desiccation and high electrical impedance. A new method has been developed which allows controllable production of small to very large lesions. This technique modifies the electric field within the tissue by interstitially infusing hypertonic saline during the application of RF energy. The present study was conducted to determine the spread of saline in prostate and resultant impedance changes. A 26 gauge needle with 5 mm exposed metal tip was inserted into the prostate of 10 canines. Impedance measurements were made between the two recording electrodes placed 12 mm apart, with the infusion electrode at the center. Hypertonic saline (14.6% NaCl) with a 35% mixture of a radiocontrast agent (Hypaque) was continuously infused at 2 ml/min through the needle electrode into the tissue for 10 minutes. Fluoroscopic images taken concomitantly with impedance measurements, were analyzed for intensity and spread of the saline concentration field. The developed concentration field was seen to modify the impedance characteristics, thereby indicating the creation of the saline-liquid electrode. This research has facilitated the development of RF hyperthermic treatment for benign prostatic hyperplasia in humans.