Real‐time conductivity imaging of temperature and tissue property changes during radiofrequency ablation: An ex vivo model using weighted frequency difference

Abstract

We demonstrated the feasibility of time difference and weighted frequency difference conductivity imaging for real-time monitoring of temperature distribution and ablation region estimation during radiofrequency (RF) ablation. The electrical conductivity spectrum of biological tissue reflects mobility of ions in intra- and extra-cellular fluids and changes in cellular morphology induced by heating. The time series conductivity spectra were measured in an ex vivo bovine liver by a high-speed electrical impedance tomography (EIT) system. The EIT system was protected by filters to suppress RF energy and allow interleaved real-time imaging. We recorded time and weighted frequency-difference conductivity images and direct temperature variations at the ablation region and control region during 8 min ablation and for the following 66 min of cooling. Conductivity variation in regions of interest was compared with temperature recordings. Contours of conductivity change were visualized and compared to estimate the ablation area. EIT images confirmed increase of conductivity at all frequencies and loss of frequency conductivity change associated with loss of cellular structure. Time difference conductivity images showed changes due to both heating during ablation and heat dissipation following ablation together with tissue property changes. Weighted frequency-difference images presented persistent changes following heating due to the morphological change in the ablation zone.

Real-time monitoring radiofrequency ablation using tree-based ensemble learning models

“…RFA treatment can start to create some physiological problems if applied without a proper monitoring mechanism due to the uncontrollable nature of thermal ablation [8]. The main aspect to be monitored is the extent of the ablation zone as the AC is applied.…”

“…Electrical impedance tomography (EIT), one of the methods that utilize the measured electrical impedance for monitoring RFA, uses electrodes surrounding the targeted tissue to measure impedance paths [16]. The data collected in EIT are then reconstructed into tissue electrical conductivity and temperature to provide lesion depth images [17][18][19]. The principle that allows for electrical impedance to be utilized is the temperature dependence of the electrical conductivity of biological tissue [20].…”

Real-time estimation of lesion depth and control of radiofrequency ablation within ex vivo animal tissues using a neural network

“…Radiofrequency ablation (RFA) is commonly used to destroy liver, kidney, lung and bone tumours and other potentially cancerous tissues. RFA heats tissue with electrodes that supply alternating electric current, which causes ionic agitation and joule heating [1][2][3][4]. When cells are exposed to the temperatures shown in Figure 1, they undergo coagulative necrosis (i.e.…”

“…Point temperature probes are included in many RFA devices, but do not provide three-dimensional lesion depths [1,2]. Feedback control requires monitoring of RFA lesion progress as tissue left unablated could locally recur (underablation); likewise, without knowledge of lesion depth, critical structures deeper within tissue could be damaged (overablation) [3][4][5].…”

“…These techniques utilise changes in tissue properties undergoing thermal ablation, including electrical, acoustic and optical behaviours. Electrical impedance tomography uses surface electrodes surrounding the tissue under evaluation to measure impedance paths that are reconstructed into tissue electrical conductivity to provide lesion depth images that can be 90%þ accurate [4,[6][7][8]. While data collection is quick, reconstruction is complex due to the requirement of solving the ill-posed three-dimensional inverse problem [6][7][8].…”