The ACE1 Electrical Impedance Tomography System for Thoracic Imaging

Abstract

The design and performance of the active complex electrode (ACE1) electrical impedance tomography system for single-ended phasic voltage measurements are presented. The design of the hardware and calibration procedures allows for reconstruction of conductivity and permittivity images. Phase measurement is achieved with the ACE1 active electrode circuit which measures the amplitude and phase of the voltage and the applied current at the location at which current is injected into the body. An evaluation of the system performance under typical operating conditions includes details of demodulation and calibration and an in-depth look at insightful metrics, such as signal-to-noise ratio variations during a single current pattern. Static and dynamic images of conductivity and permittivity are presented from ACE1 data collected on tank phantoms and human subjects to illustrate the system's utility.

Use of an optimized spatial prior in D-bar reconstructions of EIT tank data

“…In Section 5, we demonstrate the method's effectiveness by applying our new techniques to reconstructions of experimental tank data, collected using the ACE1 EIT system at Colorado State University [24]. We examine several agar phantoms representing a human heart and lungs, and we include various simulated pathologies.…”

“…Data was collected on a tank 30 cm in diameter filled with saline, on 32 electrodes, using the ACE1 EIT system at Colorado State University [24], applying adjacent current patterns with current amplitude 3.3 mA at 125 kHz. The effectiveness of the use of a prior to improve spatial resolution was tested on five experimental configurations: (i) agar targets simulating lungs and a heart with conductivities 190 mS/m for the saline, 136 mS/m for the lungs, and 238 mS/m for the heart (ii) the same agar heart and lungs with a copper pipe 1.6 cm in diameter inserted into the lower part of the lung on the right (iii) the same agar heart and lungs with a PVC pipe 2.2 cm in diameter inserted into the lower part of the lung on the right (iv) a second set of agar heart and lungs collected on a different day with conductivities 200 mS/m for the saline, 85 mS/m for the lungs, and 460 mS/m for the heart (v) the same agar heart and lungs used in (iv) with the upper half of the lung on the left removed.…”

A Parametric EIT System Spice Simulation with Phantom Equivalent Circuits

“…Although this method is characterized by critically-low spatial resolution, especially near the center of the examined volume where the field sensitivity is decreased, its temporal resolution can reach exceptional levels, making EIT a great solution for real-time and time variant applications [1,2]. In addition, in the case of medical applications where conventional imaging methods such as CT, MRI and ultrasound cannot be used frequently and repeatedly on a patient (due to radiation, high cost, non-portability etc), EIT is a possible low cost alternative; EIT can serve as a complementary diagnostic and monitoring tool between two examinations from the previous methods.…”

“…Many EIT hardware systems with specific clinical applications have been developed over the last 3 decades, such as the Sheffield MK (v1 1987MK (v1 , v3.5 2001 [3], the Dartmouth breast imaging system (1998,2001,2008) [4][5][6], the ACT 3 and 4 EIT system (1994,2005) [7,8], the Swisstom active electrode system (2012), the KHU Mark 2.5 system (2014) [9] and the ACE1 pulmonary real-time imaging system(2019) [1]. Over the years, many design and configuration improvements have taken place, targeted to the acquired medical images' quality.…”

“…Therefore, apart from the essential mathematical modelling of the problem, the measured data need to be as accurate as possible with the minimum noise level. Intrinsic electrical bio-signals and unwanted motion of the electrodes (e.g., breathing or heartbeat) introduce noise in addition to noise due to electronic hardware [1,12]. Many of these cannot be easily predicted during the hardware design process.…”