SIR 2024
Interventional Oncology
Nooshin Zeinali, MS
PhD Candidate
Kansas State University
Financial relationships: Full list of relationships is listed on the CME information page.
Jan sebek, PhD
Research Assistant Professor
Kansas State University
Disclosure information not submitted.
Austin Pfannenstiel, MBA, MS, PhD
President
Precision Microwave
Disclosure information not submitted.
To assess the technical feasibility of predicting the extent of tissue ablation between a pair of microwave ablation (MWA) applicators.
Materials and Methods:
When delivering MWA with the use of multiple applicators, there exists the opportunity to monitor power propagation between each applicator pair, i.e., measure complex transmission coefficients (CTCs), the fraction of power transmitted by an antenna and received by the other. The CTC is dependent on applicator spacing and highly variable temperature-dependent dielectric properties of the signal propagation path (tissue being ablated). To gather CTCs, MWAs were performed in ex vivo bovine liver using a pair of custom-built 2.45 GHz water-cooled applicators and a spacer for applicator distance of 3 cm. We applied power of 30 W to each applicator over durations of 46 s, 184 s, and 460 s (n = 3 repetitions for each time point). For each experiment, CTC was acquired at 0 s and then every 46 s until the end of the respective MWA duration. To show the feasibility of ablation extents prediction, we developed a linear regression model for relation between gathered CTCs and the ground truth ablation zones, as observed by the extent of visibly discolored tissue from cross-section of the ablated tissue sample. The transient changes of both CTCs as well as ground truth ablation extents over the course of the ablation were approximated using an exponential function and normalized for the purpose of comparison.
Results:
The normalized average transmission coefficient initially experienced a swift decline over 70 s [46 - 92 s], with an inflection point followed by a rapid ascent, before gradually nearing a steady state. By leveraging the linear regression mapping between the two datasets, we were able to estimate the ablation extent using the processed microwave transmission coefficient data. When comparing the transmission coefficient data to the reference standard, the prediction error regarding the completion time for ablation was approximately 1.07%. Analysis of these datasets indicated complete ablation between the two antennas is likely to have occurred between 250 and 350s.
Conclusion:
We have illustrated the potential of employing microwave transmission coefficient measurements as a tool to monitor the dynamic progression of thermal ablation zones in ex vivo tissue samples. This approach offers an avenue for real-time tracking of thermal ablation that may inform the time at which ablations should be terminated and post-treatment images acquired.