Ex-Vivo Characterization of Bioimpedance Spectroscopy of Normal, Ischemic and Hemorrhagic Rabbit Brain Tissue at Frequencies from 10 Hz to 1 MHz

Abstract

Stroke is a severe cerebrovascular disease and is the second greatest cause of death worldwide. Because diagnostic tools (CT and MRI) to detect acute stroke cannot be used until the patient reaches the hospital setting, a portable diagnostic tool is urgently needed. Because biological tissues have different impedance spectra under normal physiological conditions and different pathological states, multi-frequency electrical impedance tomography (MFEIT) can potentially detect stroke. Accurate impedance spectra of normal brain tissue (gray and white matter) and stroke lesions (ischemic and hemorrhagic tissue) are important elements when studying stroke detection with MFEIT. To our knowledge, no study has comprehensively measured the impedance spectra of normal brain tissue and stroke lesions for the whole frequency range of 1 MHz within as short as possible an ex vivo time and using the same animal model. In this study, we established intracerebral hemorrhage and ischemic models in rabbits, then measured and analyzed the impedance spectra of normal brain tissue and stroke lesions ex vivo within 15 min after animal death at 10 Hz to 1 MHz. The results showed that the impedance spectra of stroke lesions significantly differed from those of normal brain tissue; the ratio of change in impedance of ischemic and hemorrhagic tissue with regard to frequency was distinct; and tissue type could be discriminated according to its impedance spectra. These findings further confirm the feasibility of detecting stroke with MFEIT and provide data supporting further study of MFEIT to detect stroke.

EIT Imaging of Intracranial Hemorrhage in Rabbit Models Is Influenced by the Intactness of Cranium

“…Intuitively, as blood impedance ( 1.4 Ω ·m ) is much smaller than the impedance of cerebral parenchyma ( 8.5 Ω ·m ) [14], it appears that the whole brain impedance should decline when blood is injected under both open and closed cranium conditions. Nevertheless, by comparing and analyzing the differences between open and closed cranium conditions, it is reasonable to speculate that the ICH model established under two different conditions might be physiologically distinct.…”

“…Electrical impedance tomography (EIT) is a real-time, portable, noninvasive, functional imaging technique, which aims to reconstruct the electrical impedance distribution (or the change in electrical impedance) inside the human body by safely injecting a set of currents into the body via surface electrodes and measuring the resulting voltages from different types of tissues [12]. Because there are significant differences in impedance between blood (hematoma) and normal brain tissue [13, 14], EIT can potentially be used to detect and monitor ICH at bedside.…”

Electrical Impedance Changes at Different Phases of Cerebral Edema in Rats with Ischemic Brain Injury

“…In our study, we established the impedance measurement system by employing a 1260 Impedance/Gain-Phase Analyzer (Solartron Analytical, Farnborough, UK) with a 1294A interface, controlled by the Zplot software (Scribner Associates Inc., Southern Pines, NC, USA), as shown in Figure 3 . Additionally, the four-electrode method was adopted to measure the brain tissue impedance spectra because this strategy can significantly reduce the impact of electrode-tissue contact impedance [ 12 ]. Accordingly, a measurement box developed by our group was used to load the brain tissue for impedance measurement.…”

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

“…Lately, fdEIT, which recovers the frequency-dependent impedance changes by employing the differential results of boundary voltages simultaneously measured at different frequencies, was suggested to detect stroke because the impedances of stroke lesions and normal tissues exhibit distinct frequency-dependent properties [12, 13]. Although considerable advancements in fdEIT used for stroke detection have been made over recent years [5, 6], the effect of electrode-skin contact impedance on the boundary voltage measurement of fdEIT is still a challenging problem.…”