Tetrapolar measurement of cervical tissue structure using impedance spectroscopy

The aim was to see if cervical tissues could be differentiated in terms of their impedance spectra. Transfer impedance data over the frequency range 9.6-1200 kHz were collected from the cervix in 44 women. A tetrapolar surface electrode probe was used with an electrode separation such that the volume of sensitivity extends to a depth of approximately 400 /spl mu/m in the tissue. Published microscopy data showing the cell structures associated with normal squamous epithelium, columnar tissue and various pre-malignant stages was used to set up 3200 node electrical mesh models including the cell membranes and cell arrangements. These models showed that differences in transfer impedance spectra could be expected from the different tissue structures. Predicted spectra for normal and premalignant tissues have been tested against measured data from patients. Confirmation of tissue type was by biopsy and observation during colposcopy. Impedance spectra have been fitted to a Cole type equation in the impedance plane and very significant differences have been found between columnar and normal squamous epithelial tissues. There is good agreement between the model predictions and the measured impedance spectra. It is shown that data collected from high grade cancer-in-situ tissues are well separated from normal squamous epithelial tissues.