A Simple instrumentation calibration technique for Electrical Impedance Tomography (EIT) using a 16-electrode phantom.
ABSTRACT A simple analog instrumentation for electrical impedance tomography is developed and calibrated using the practical phantoms. A constant current injector consisting of a modified Howland voltage controlled current source fed by a voltage controlled oscillator is developed to inject a constant current to the phantom boundary. An instrumentation amplifier, 50 Hz notch filter and a narrow band pass filter are developed and used for signal conditioning. Practical biological phantoms are developed and the forward problem is studied to calibrate the EIT-instrumentation. An array of sixteen stainless steel electrodes is developed and placed inside the phantom tank filled with KCl solution. 1 mA, 50 kHz sinusoidal current is injected at the phantom boundary using adjacent current injection protocol. The differential potentials developed at the voltage electrodes are measured for sixteen current injections. Differential voltage signal is passed through an instrumentation amplifier and a filtering block and measured by a digital multimeter. A forward solver is developed using finite element method in MATLAB 7.0 for solving the EIT governing equation. Differential potentials are numerically calculated using the forward solver with a simulated current and bathing solution conductivity. Measured potential data is compared with the differential potentials calculated for calibrating the instrumentation to acquire the voltage data suitable for better image reconstruction.
- SourceAvailable from: Tushar Kanti BeraJournal of Electrical Bioimpedance. 03/2011; 2:2-12.
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ABSTRACT: Surface electrodes are essentially required to be switched by analogue multiplexers operating with a set of parallel digital data for boundary data collection in electrical impedance tomography EIT. A 16 electrode EIT system needs 16-bit parallel digital data to operate the multiplexers. More electrodes in an EIT system require more digital data bits. In this paper, a common ground current injection method is proposed for a 16 electrodes EIT system to switch the electrodes with reduced number of digital data. Common ground method needs only two 16:1 multiplexers operating with only 8-bit parallel digital data. Boundary data are collected from practical phantoms by injecting a constant current using common ground method. Resistivity images are reconstructed in EIDORS and the results are compared with the images obtained in opposite current pattern. Reconstructed images obtained with common ground method are found similar to the images obtained with the conventional opposite current pattern.International Journal of Communication Networks and Distributed Systems 11/2014; 12(1):47-68.
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ABSTRACT: Multifrequency Electrical Impedance Tomography (EIT) is preferred for imaging of biomedical objects to study their wide range of tissue conductivity profiles among different type of subjects under test. In this direction, a multifrequency EIT system is developed for biomedical imaging and the resistivity imaging of a practical phantom is studied at different frequencies. Practical biological phantoms are developed with NaCl solution as the bathing medium and vegetable tissue cylinders as the inhomogeneity. A sinusoidal constant current is injected to the boundary of the practical phantoms at different frequency levels and the surface potentials are measured. Resistivity images are reconstructed from the boundary potential data using EIDORS and images are analyzed with image contrast parameters. Results show that the instrumentation part of the developed EIT system injects constant current at different frequency levels and measures the boundary potential data. Boundary data are successfully generated for all the frequencies and found suitable for image reconstruction. CNR, PCR and COC of the resistivity images show that the resistivity images are efficiently reconstructed from the boundary data acquired from the multifrequency EIT system.IEEE International Conference on Signal Processing and Communications (SPCOM 2012), Bangalore, India; 01/2012