Basic study of a new diagnostic modality by non-invasive measurement of the electrical impedance tomography (EIT) on localized tissues

Information on biological tissues for medical diagnoses can be usually provided by X-ray images, ultrasonic images and MRI, which offer basically the information on mass or proton density distributions. On the other hands, electrical bioimpedances contain different information related to tissue structures and their physiological states and functions. It is well known that the electrical properties of biological tissues differ significantly depending on their structure. This has been reported by investigators studying the application of differences in the electrical properties of tumors to the clinical aspect. Electrical properties of malignant breast tumors have been investigated by Frinke and Morse. They found significantly higher permeability of the tumor tissue at 20 kHz compared to normal or nonmalignant tissues. Similar results have been reported by several other investigations. Our group has measured directly electrical impedances of benign breast tumor and malignant breast tumor by needle electrodes. Our group has developed the non-invasive electrical impedance tomography ( EIT ). The purposes of this study were to estimate the electrical conductivity of localized tissues by non-invasive measurement of the electrical impedance tomography ( EIT ) on localized tissues. This EIT methods has a possibility of early detection of breast cancer and can be used for young women breast cancers which are difficult to be found by mammography because of dense breasts. In this conference, we illustrate our new theory of non-invasive measurement of EIT. Our group ( Department of Surgery of The University of Tokushima and Institute of Technology and Science of The University of Tokushima ) has studied and developed EIT since 1980s and has experimented with non-invasive measurement of EIT since 2000s. A new impedance analytical system was developed, and measurements were performed over a frequency range of 0-100kHz by the four-electrode method. The biological tissue can be regarded electrically as an equivalent consisting of extracellular resistance ( Re ), intracellular resistance ( Ri ), and electrical capacitance of the cell membrane ( Cm ). These three parameter were calculated from the measured values of electrical bio-impedance by the curve-fitting technique using a computer program. It was found that Re and Ri of breast cancers were significantly lower than those of benign tumors, and that Cm of breast cancers was significantly lower than that of benign tumors. Ito Laboratory, Department of Medical System Engineering at Chiba University developed an organism equivalence phantom. Our group used the phantom and made one-layer phantom ( muscle or brain ) and two-layers phantom ( muscle and brain ). Our group measured the electrical conductivity of these one layer and two layers phantoms by our non-invasive measurement of EIT. One-layer phantom was measured by our non-invasive measurement of EIT. The errs of impedance between measured by our new EIT and by ordinary method were whthin 5 %. These results were satisfactorily and proved that one-layer muscle or brain could be measured correctly by our new measurement . But two-layers ( muscle and brain ) phantom was measured by our non-invasive measurement of EIT, the errs of impedance were over 20%. These results were unsatisfactorily. These results suggest that one layer tissues of muscle or brain can be diagnosed by our non-invasive measurement of EIT. Now we are making an improved two layers phantome which are muscle and fat tissue and measure these impedances. If we will be able to a make multi- layers phantom and measure these impedances correctly, our new method will be used by early breast cancer screening.