In vivo electrical impedance measurements during and after electroporation of rat liver.

Electroporation is used for in vivo gene therapy, drug therapy and minimally invasive tissue ablation. Applying electrical pulses across cells can have a variety of outcomes; from no effect to reversible electroporation to irreversible electroporation. Recently, it has been proposed that measuring the passive electrical properties of electroporated tissues could provide real time feedback on the outcome of the treatment. Here we describe the results from the impedance characterization (single dispersion Cole model) for up to 30 min of the electroporation process in in vivo rat livers (n=8). The electroporation sequence consisted of 8 pulses of 100 micros with a period of 100 ms. Half of the animals were subjected to field magnitudes considered to have reversible effects (R group, E=450 V/cm) whereas for the other half irreversible field amplitudes were applied (I group, E=1500 V/cm). As expected, there was an immediate increase of conductivity (R group Deltasigma/sigma(t=0)=9+/-3%; I group Deltasigma/sigma(t=0)=43+/-1%). However, the overall long term pattern of change in conductivity after electroporation is complex and different between reversible and irreversible groups. This suggests the superposition of different phenomena which together affect the electrical properties.