In vivo EIS characterization of tumour tissue properties is dominated by excess extracellular fluid.

Electrical impedance spectroscopy (EIS) is a non-ionizing, non-invasive technique which can be used to detect the presence of malignant tumours based on their electrical properties. Although it has been suggested that the edema which accompanies tumours strongly influences EIS tumour characterization, such information has not, until now, been documented in the literature. Growing intramuscular rodent tumours were imaged using magnetic resonance imaging (MRI) and EIS at several time points post-tumour implantation. The amount of edema associated with the tumours was calculated from the MRI images. Electrical parameters (resistivity, permittivity, fluid index ratio and peak frequency) were extracted from the EIS spectra. Taken together, the resulting electrical parameters strongly indicate that edema is the dominating pathological feature in EIS characterization and can at times conceal the presence of the tumour. Receiver operating characteristic analysis supports these findings.