Electric and Thermal Field Effects in Tissue Around Radiofrequency Electrodes

TLDR

The study investigates the spatial and temporal distribution of electric and thermal fields around an RF electrode used for pain therapy. Finite‑element modeling of electric and thermal fields around the RF electrode was performed and validated against ex vivo liver and egg‑white tissue measurements, including continuous and pulsed RF scenarios with sensor‑equipped cannulae. Measured rapid temperature spikes and high electric fields during pulsed RF matched finite‑element predictions, confirming that pulsed RF can produce destructive heat lesions and membrane disruption while continuous RF causes heat‑mediated neuronal destruction.

Abstract

A study is carried out of the spatial distribution and time dependence of electric and thermal fields in the tissue around a radiofrequency (RF) electrode used in pain therapy. Finite-element calculation of the fields is performed, and results are compared with ex vivo tissue data. Field predictions are made for continuous and for pulsed RF applications.A special RF cannula electrode is constructed with both macro and micro thermocouple sensors to measure both average and rapid, transitory temperature effects. Temperatures and impedances are recorded in liver and egg-white models using signal outputs from a commercially available RF lesion generator. These data are compared with the results of finite-element calculations using electric field equations and the bio-heat equation.Average and pulsatory temperatures at the RF electrode are measured. Rapid temperature spikes during pulsed RF bursts are observed. These data compared well with theoretical calculations using known electrical and thermal tissue parameters.Continuous RF lesioning causes heat destruction of neurons. Pulsed RF lesioning (PRFL) produces heat bursts with temperatures in the range associated with destructive heat lesions. PRFL also produces very high electric fields that may be capable of disrupting neuronal membranes and function. Finite-element calculations agree substantially with the measured data, giving confidence to their predictions of fields around the RF electrode.