Raman microspectroscopic detection of thermal denaturation associated with irreversible electroporation

Irreversible electroporation (IRE) is a less-invasive treatment for ablating tumors. It delivers a train of electric pulses to the cells deep inside the tissue via puncturable electrodes and yields fatal breakdown of the cell membrane around the electrodes. Thermal damage associated with the pulse application is avoidable insofar as the optimal pulse conditions are selected to minimize Joule heating. However, the application of long, intense, and repetitive pulses comes with the risk of a temperature rise around the electrodes. Therefore, the aim of this study was to provide a quantitative evaluation of IRE-induced thermal denaturation at the level of the molecular structure. A tissue phantom containing albumin was observed with a confocal Raman microscope after an IRE protocol. The Raman imaging and subsequent analysis successfully indicated albumin denaturation around the electrodes. The extent of denaturation correlated well with the temperature rise in the tissue that was detected using temperature-sensitive ink. The maximal temperature rise in the experiment also agreed well with that estimated using finite element analysis. Another important finding was that the temperature rise and the consequent denaturation were more significant at the cathode than at the anode, despite the symmetric distribution of the electric field around the electrodes. This implies the occurrence of an unexpected side effect of the IRE.