A Parametric EIT System Spice Simulation with Phantom Equivalent Circuits

Abstract

In this paper a number of LT Spice simulations have been carried out on an Electrical Impedance Tomography (EIT) system, which includes the whole analog and digital circuitry as well as the subject to be examined (phantom model). The aim of this study is to show how the analog and digital parts, the electrodes and the subject’s physical properties may impact the measurements and the quality of the reconstructed image. This could provide a useful tool for designing an EIT system. Special attention has been given to the current source’s output impedance and swing, to the noise produced by the circuits and to the Analog to Digital Converters (ADCs) resolution and sampling rate. Furthermore, some 3D phantom subjects have been modeled and simulated as equivalent circuits, merged with the EIT simulated hardware, in order to observe how changes on their properties interact with the whole circuitry and affect the final result. Observations show that mirrored current sources with z o u t > 350 k Ω and sufficiently high ADC acquisition sampling rate ( f s a m p l e ≥ 16 f i n ) can result to accurate impedance measurements and therefore quality image reconstruction within a frequency span of at least 10 to 100 kHz. Moreover, possible hardware failures (electrode disconnections and imbalanced contact impedances) can be detected with a simple examination of the first extracted image and measurement set, so that by direct modification of the reconstruction process, a corrected result can be obtained.

Analog Realization of Fractional-Order Skin-Electrode Model for Tetrapolar Bio-Impedance Measurements

“…R b is the resistance to be measured in each case. Finally, two 20 pF parasitic capacitors are included for both voltage output traces to include any possible stray capacitive effects [21,22]. Figure 27.…”

“…Proper modelling of the tissues under test electrical characteristics is a crucial step during the design process of bio-impedance measurement systems. To this end, designers simulate and employ equivalent circuits of the SUT [21][22][23][24], usually implemented using lumped passive elements (capacitors and resistors). By utilizing different values of resistors and capacitors, they can simulate different measurement scenarios and setups in order to both determine the measurement system's specifications and simulate its performance.…”

Analysis, Simulation, and Development of a Low-Cost Fully Active-Electrode Bioimpedance Measurement Module

“…Furthermore, a THS413 fullydifferential voltage amplifier is used to drive two 180-degrees phase shifted sinusoidal input voltage signals to two selected active electrode modules. This activates the corresponding HCPs to function in mirrored topology mode, which theoretically doubles the VCCS' output impedance [18,49]. The THS413 is built on an individual PCB board (not on the active electrode modules), which is connected to the active electrode modules via equallength SMA cables.…”

Evaluation of Thoracic Equivalent Multiport Circuits Using an Electrical Impedance Tomography Hardware Simulation Interface

“…mesh circuit equivalents to basic EIT circuitry for SPICE simulation and image reconstruction was presented in [27], where the impact of electrode short-circuit or disconnection was simulated. This approach was extended in [28] where simulations on 3D saline tank equivalents were performed under single ended and mirrored Howland current pumps. The DAC and ADC functions were also simulated in MATLAB, and results were acquired and compared for 2 current signal frequencies and 2 ADC sampling rates.…”

“…In this paper, the SPICE-MATLAB EIT simulation interface described in [28,29] is applied to three-dimensional thoracic structures. In specific, two fine F.E.…”