A fundamental study on parameter estimation of layerd local tissue impedance for EIT.

Electrical Impedance Tomography (hereinafter referred to as EIT) is 2-D or 3-D image of electrical impedance distribution in a living tissue. Unlike usual imaging methods, i.e., Xray-CT, MRI and US Imagings, EIT is used for imaging the information of tissue structure and functions. This paper provides a new estimation method as a fundamental study to realize a EIT for local biological tissue. Up until now we has proposed a new configuration of the electrodes, called divided electrode, for a high-speed measurement of bio-impedance in a cross section of a local tissue. The cross section of the tissue was represented by space distributed equivalent circuits of tissue structure known, and their parameters were estimated by inverse algorithm. In this paper, we try to estimate the parameter value of a layered structural model, the thickness of the layer, and the boundary without using US-imaging by using the divided electrode. Its capability is examined by computer simulations, where a distributed equivalent circuit is used as a model of the tissue. Estimation of impedance parameter is carried out by use of the Gauss-Newton method. Usefulness of the proposed method is confirmed by computer simulations using a typical layered tissue model.