| Electrical impedance spectroscopic (EIS) monitoring of photodynamic therapy (PDT) was investigated in rat tumor and liver in vivo, and multicellular spheroids in vitro. Non-invasive impedance monitoring of PDT in a rat muscle/tumor model showed that low-frequency impedance changed by two-fold relative to pre-treatment values. Continuously measured liver impedance altered during and after Photofrin-PDT, with changes in conductivity at ∼10 kHz, and of permittivity at ∼30 kHz and 1 MHz. Edema was related to EIS in both animal models; cell necrosis and vascular disruption in the liver were also related to impedance. Photofrin PDT-treated spheroids experienced dose-dependent drops in permittivity and conductivity at frequencies above 10 and 100 kHz, respectively. EIS distinguished between necrotic, apoptotic, and PDT-induced damage, with histology indicating that cell distribution and membrane integrity are important EIS factors. In conclusion, EIS is sensitive to PDT-induced damage, varies with dose and time, and can be correlated qualitatively to biological changes. |
