The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz

Abstract

Frequency-difference electrical impedance tomography (fdEIT) reconstructs frequency-dependent changes of a complex impedance distribution. It has a potential application in acute stroke detection because there are significant differences in impedance spectra between stroke lesions and normal brain tissues. However, fdEIT suffers from the influences of electrode-skin contact impedance since contact impedance varies greatly with frequency. When using fdEIT to detect stroke, it is critical to know the degree of measurement errors or image artifacts caused by contact impedance. To our knowledge, no study has systematically investigated the frequency spectral properties of electrode-skin contact impedance on human head and its frequency-dependent effects on fdEIT used in stroke detection within a wide frequency band (10 Hz-1 MHz). In this study, we first measured and analyzed the frequency spectral properties of electrode-skin contact impedance on 47 human subjects’ heads within 10 Hz-1 MHz. Then, we quantified the frequency-dependent effects of contact impedance on fdEIT in stroke detection in terms of the current distribution beneath the electrodes and the contact impedance imbalance between two measuring electrodes. The results showed that the contact impedance at high frequencies (>100 kHz) significantly changed the current distribution beneath the electrode, leading to nonnegligible errors in boundary voltages and artifacts in reconstructed images. The contact impedance imbalance at low frequencies (<1 kHz) also caused significant measurement errors. We conclude that the contact impedance has critical frequency-dependent influences on fdEIT and further studies on reducing such influences are necessary to improve the application of fdEIT in stroke detection.

Impedance Study of Dopamine Effects after Application on 2D and 3D Neuroblastoma Cell Cultures Developed on a 3D-Printed Well

“…Due to a sinusoidal dependence of the external voltage on time, researchers have defined the impedance of a cell filled with KCl solution and investigated the frequency dependence of its real and imaginary parts. In general, a wide frequency range is preferred in order to improve the efficiency in impedance measurements [42]. The impedance interface of the metal-electrolyte plays a fundamental role in the low frequencies (<100 Hz) [43].…”

Real-Time Detection of Hemothorax and Monitoring its Progression in a Piglet Model by Electrical Impedance Tomography: A Feasibility Study

“…v i,j is the boundary voltage of the measurement electrode pair j when the current is excited through the electrode pair i. In practice, the voltage difference caused by electrode-skin contact impedance is much larger than that resulted from the impedance of internal body tissue [39]. Moreover, the contact impedance often changes with time due to various inevitable factors such as perspiration, temperature change, patient movement, and manipulations by clinical staff [40].…”

Efficient Multitask Structure-Aware Sparse Bayesian Learning for Frequency-Difference Electrical Impedance Tomography

“…While the overwhelming majority of EIT clinical images have been produced using time-difference data, frequencydifference EIT (fdEIT) has received fewer attention in the literature and is at an earlier stage of development [6]- [10]. fdEIT uses voltage data sets with multiple excitation frequencies to calculate an image of the corresponding changes of conductivity.…”

“…As such, not only is it capable of effectively eliminating common boundary geometry errors as in timedifference EIT (tdEIT) [11], it also allows for removing body movement induced artifacts provided data collection is fast. In addition, fdEIT is more suitable for breast tumor or stroke type classification, where time reference data are not available, and frequency-dependent conductivity spectra of specific tissues are able to provide additional diagnostic information to current EIT systems [10]- [12]. However, as changes of conductivity with frequency are generally insignificant compared with conductivity changes during a moderate time interval in tdEIT, the measurements in fdEIT are very sensitive to noise [13].…”