In situ measurement of tissue temperature and bio-impedance during thermal ablation

Abstract

Thermal ablation has been an effective treatment for in situ tumor killing. It is a minimal invasive technique which can offer a fast recovery time compared with chemotherapy and radiation. The monitoring of the thermal dose applied to the targeted site is currently achieved by inserting an additional thermocouple near the target site or by measuring the large area impedance change across two ablation catheters. Precisely measuring local ablation temperature is beneficial to optimize the treatment outcome. However, it is difficult to measure both temperature and impedance in a localized area without sacrificing the invasiveness. In this thesis, impedance sensor and thermal-resistive sensor are fabricated on the surface of a glass capillary tube with 1mm outer diameter. The thermal-resistive sensors were calibrated to have an average temperature of coefficient of resistance (TCR) of 0.00161±5.9% °C -1 with an accuracy of ±0.7 °C. For the impedance sensor, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was electro-polymerized on the 300 μm diameter gold disc electrodes. The electrode interface impedance was reduced from 408 kΩ to 3.7 kΩ at a frequency of 100 Hz. Fittings from the Randles equivalent circuit model shows a two-order improvement in the electrode capacitance from 7.29 nF to 753 nF. The device had successfully demonstrated a real-time in situ measurement of both tissue temperature and tissue impedance during laser thermal ablation. The ex-vivo porcine liver laser ablation test, the device-recorded temperature had reached over 70 °C in less than 5 minutes and the tissue impedance dropped by 50%. This device integrated two measurement functions onto one thermal ablation probe without increasing the invasiveness which promotes the laser ablation technique to smaller scale for more precise therapeutics.