In Situ Monitoring of Electric Field Distribution in Mouse Tumor during Electroporation

Published Online:Aug 19 2014https://doi.org/10.1148/radiol.14140311

Abstract

MR electric impedance tomography enables reconstruction of electric field distribution by allowing measurement of the electric current density distribution and electric conductivity of the treated subject during application of electric pulses by using MR imaging and numeric algorithms.

Purpose

To investigate the feasibility of magnetic resonance (MR) electric impedance tomography (EIT) technique for in situ monitoring of electric field distribution during in vivo electroporation of mouse tumors to predict reversibly electroporated tumor areas.

Materials and Methods

All experiments received institutional animal care and use committee approval. Group 1 consisted of eight tumors that were used for determination of predicted area of reversibly electroporated tumor cells with MR EIT by using a 2.35-T MR imager. In addition, T1-weighted images of tumors were acquired to determine entrapment of contrast agent within the reversibly electroporated area. A correlation between predicted reversible electroporated tumor areas as determined with MR EIT and areas of entrapped MR contrast agent was evaluated to verify the accuracy of the prediction. Group 2 consisted of seven tumors that were used for validation of radiologic imaging with histopathologic staining. Histologic analysis results were then compared with predicted reversible electroporated tumor areas from group 1. Results were analyzed with Pearson correlation analysis and one-way analysis of variance.

Results

Mean coverage ± standard deviation of tumors with electric field that leads to reversible electroporation of tumor cells obtained with MR EIT (38% ± 9) and mean fraction of tumors with entrapped MR contrast agent (41% ± 13) were correlated (Pearson analysis, r = 0.956, P = .005) and were not statistically different (analysis of variance, P = .11) from mean fraction of tumors from group 2 with entrapped fluorescent dye (39% ± 12).

Conclusion

MR EIT can be used for determining electric field distribution in situ during electroporation of tissue. Implementation of MR EIT in electroporation-based applications, such as electrochemotherapy and irreversible electroporation tissue ablation, would enable corrective interventions before the end of the procedure and would additionally improve the treatment outcome.

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Article History

Received February 6, 2014; revision requested April 17; revision received May 26; accepted June 9; final version accepted June 18.
Published online: Aug 19 2014
Published in print: Jan 2015

Vol. 274, No. 1

Funding/Support

Supported by the Slovenian Research Agency (ARRS) and conducted within the scope of the Electroporation in Biology and Medicine European Associated Laboratory (LEA-EBAM).

Abbreviations

Abbreviations:
C_MREIT	coverage of tumors with electric field that leads to reversible electroporation of tumor cells obtained with MR EIT
EIT	electric impedance tomography
F_Gd-DOTA	tumor fraction with entrapped Gd-DOTA
F_LYint	tumor fraction with LY-positive fluorescence
Gd-DOTA	gadolinium tetraazacyclododecane tetraacetic acid meglumine
LY	Lucifer yellow

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