Performance Evaluation of Five Types of Ag/AgCl Bio-Electrodes for Cerebral Electrical Impedance Tomography

Abstract

Electrical impedance tomography (EIT) is an emerging medical imaging technique, which has already been investigated in several clinical applications due to its low-cost, non-invasiveness, non-radioactivity, high temporal resolution, and great sensitivity to impedance changes. One potential use of EIT is to perform long-term continuous imaging monitoring of brain for patients who suffer from severe cerebral diseases. However, this application requires a demanding performance of electrodes because of the characteristics of cerebral EIT measurements. Although Ag/AgCl bio-electrodes are widely used for clinical practices or EIT research at the moment, influences of different types of Ag/AgCl electrodes on cerebral EIT measurements have not been investigated. In this study, five common types of Ag/AgCl bio-electrodes were put into comparison by measuring the forearm and the brain of 10 healthy adult volunteers and evaluating those data in frequency or time domain in terms of contact impedance, uniformity, signal-to-noise ratio, and stability. Results show that Ag/AgCl powder electrode has an overall best performance with as low contact impedance as commercial ECG electrodes (p > 0.05), high SNR (60.3 ± 4.5 dB), better uniformity (coefficient of correlation 0.95 ± 0.03), and greater stability (slope 0.68 ± 0.03). After further improvement in design and instrumentation, Ag/AgCl powder electrode is likely to become the optimal choice for cerebral EIT measurements and provide feasible technical support for further research or application in cerebral EIT.

A Versatile and Reproducible Multi-Frequency Electrical Impedance Tomography System

“…The SNR in the scalp recordings was decreased further in some recordings by artefacts resulting from subject or electrode movement. Between patients the SNR ranged from 41.6 to 56.0 dB, equivalent to 0.18% to 0.94%, which was less than the 2% observed by Romsauerova et al [20] using a similar current amplitude and frequency, and within the 37.9 to 62.8 dB range observed by Xu et al [41] using an order of magnitude greater amplitude at 50 kHz. Thus the ScouseTom system offers comparable or greater performance to existing systems, but with increased versatility in experimental settings.…”

Fabrication of Micro-Needle Electrodes for Bio-Signal Recording by a Magnetization-Induced Self-Assembly Method

“…In order to better understand the effect of insertion force on EII recording, the EII recording properties of the ME during the insertion process were tested. The left inner forearm was chosen as the measurement site due to its features of less hair and thinner stratum corneum [ 10 , 26 ]. The speed of the linear motor was 0.5 mm/s; the injection voltage of the LCR meter was 1 V; and its frequency was 50 Hz.…”

In Vivo Imaging of Twist Drill Drainage for Subdural Hematoma: A Clinical Feasibility Study on Electrical Impedance Tomography for Measuring Intracranial Bleeding in Humans

“…Meanwhile, it must be realized that the detection of intracranial bleedings by EIT may still be challenging due to the existence of the skull [34]. The signals of intracranial resistivity changes may be attenuated by the resisting effect of the skull because it has an extremely higher resistivity as compared to brain parenchyma and shows resistivity inhomogeneity with different parts [31].…”