Dynamic electrical impedance imaging with the interacting multiple model scheme

Frequency-division multiplexing for electrical impedance tomography in biomedical applications

Electrical impedance tomography (EIT) produces an image of the electrical impedance distribution of tissues in the body, using electrodes that are placed on the periphery of the imaged area. These electrodes inject currents and measure voltages and from these data, the impedance can be computed. Traditional EIT systems usually inject current patterns in a serial manner which means that the impedance is computed from data collected at slightly different times. It is usually also a time-consuming process. In this paper, we propose a method for collecting data concurrently from all of the current patterns in biomedical applications of EIT. This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once. The signals from various current injecting electrodes are separated by injecting different frequencies through each electrode. This is called frequency-division multiplexing (FDM). At the voltage measurement electrodes, the voltage related to each current injecting electrode is isolated by using Fourier decomposition. In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency. Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast. This method allows simultaneous measurements of all the current patterns, which may be important in applications where the tissue changes occur in the same time scale as the measurement. We discuss the FDM EIT method from the biomedical point of view and show results obtained with a simple experimental system.

Methods of optimization of electrical impedance tomography for imaging tissue electroporation

Tissue electroporation is a medical technique in which electrical pulses of microsecond to millisecond length are applied to a tissue in order to permeabilize the membrane of targeted cells, either temporarily or permanently, for the purpose of drug delivery and gene therapy or tissue ablation, respectively. Electrical impedance tomography (EIT) has been suggested as an effective means of imaging the treated area and thereby providing control of electroporation. In this simulation based study we introduce methods for optimizing the use of EIT under the special conditions of electroporation. First, we address the issue of the rapid changes in tissue conductivity, during and after the application of pulses. We propose a solution through a method of simultaneously collecting data from all the electrodes, essentially capturing the state of the tissue at a single instant. This method, which employs several distinct frequencies, one for each electrode, allows a speedy and continuous collection of data, a vital part of real-time electroporation monitoring. The second issue is taking advantage of the presence of electroporation electrodes for the EIT process. We show how the electroporation electrodes that are normally found inside the tissue may help improve the reconstruction compared to data collected only from the body's boundary. This mathematical study employs recently collected in vivo data of rat liver electroporation to obtain a model which represents, as closely as possible, the reality of electroporation procedures.