EVALUATION OF THE SENSITIVITY OF THE MEASURING CHANNEL OF THE DEVICE FOR THE COLLECTION AND DATA TRANSFER FOR ELECTRIC IMPEDANCE TOMOGRAPHY

Abstract

Electrical impedance tomography is a promising method of medical imaging that allows re-constructing the conduction field inside the object (or changing it) based on electrical measurements on the surface of a conductive object. To do this, a low-frequency high-frequency electric current of small amplitude is passed through the object under study and potentials on the surface of the object under study are simultaneously recorded. The sensitivity of the method is determined by the sensitivi-ty of the measuring channel of the device for collecting and transmitting data for electrical imped-ance tomography. The paper presents a study of the sensitivity of the measuring channel of a data acquisition and transmission device for electrical impedance tomography. The work presents a de-vice for collecting and transmitting data for electrical impedance tomography, built on the basis of the input / output board L-CARD E502, as well as the measuring channel of this device. The measur-ing channel consists of a pair of measuring multiplexers, a programmable differential amplifier and an analog-to-digital converter. The effect of the multiplexer resistance on the result of measuring potential differences is estimated. The theoretical sensitivity limit of the device is estimated based on the bit depth of the analog-to-digital converter and the maximum gain of the programmable differen-tial amplifier. The theoretical limit of sensitivity of the measuring channel as part of a data acquisi-tion and transmission device for electrical impedance tomography was 1.22 mOhm. The reasons for the impossibility of reaching the theoretical limit of sensitivity are described using the test load as an example. As a test load, a ring of resistors is considered, as well as a ring of resistors with an addi-tional node in the center connecting nodes on the periphery through the resistor. Based on the circuit simulation of the test load in the MicroCAP circuit simulation environment, an estimate of the real sensitivity limit of the device, which amounted to 35 mOhm, is given. In the course of the experiment, a change was made in the resistor in the potential registration region, followed by an assessment of the voltage change in the potential registration region. Increasing the sensitivity is possible in two ways: by increasing the bit depth of the analog-to-digital converter or by increasing the gain of the measuring channel by introducing additional amplification stages.