Simulated characterization of atherosclerotic lesions in the coronary arteries by measurement of bioimpedance (original) (raw)
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Simulation of electrode impedance and current densities near an atherosclerotic lesion
2nd Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.02EX578)
A four-point electrode measuring impedance in the vicinity of an atherosclerotic lesion was modeled using FEM software. The simulation modeled the electrodes as being attached to an angioplasty balloon in a coronary artery. Impedance was calculated when the "balloon" was uninflated (not in contact with the lesion) and inflated (in contact with the lesion). Additionally, different lesion types (Va and Vb, as defined by the American Heart Association) and the effects of the low-conductivity calcium layer were considered. Results showed that the real component of the impedance was much higher when the electrodes were in contact with lesion. Also, when the electrodes were in direct physical contact with the lesion, the difference between various lesion morphologies could be seen by observing the differences in the imaginary and phase component of the impedance. As a consequence of these simulations, it appears plausible that four-point electrodes mounted to an angioplasty balloon may be useful in determining whether a balloon has made contact with a lesion, and in characterizing that lesion.
Electrochemical impedance spectroscopy to characterize inflammatory atherosclerotic plaques
Biosensors and Bioelectronics, 2011
Despite advances in diagnosis and therapy, atherosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in the Western world. Predicting metabolically active atherosclerotic lesions has remained an unmet clinical need. We hereby developed an electrochemical strategy to characterize the inflammatory states of high-risk atherosclerotic plaques. Using the concentric bipolar microelectrodes, we sought to demonstrate distinct Electrochemical Impedance Spectroscopic (EIS) measurements for unstable atherosclerotic plaques that harbored active lipids and inflammatory cells. Using equivalent circuits to simulate vessel impedance at the electrode-endoluminal tissue interface, we demonstrated specific electric elements to model working and counter electrode interfaces as well as the tissue impedance. Using explants of human coronary, carotid, and femoral arteries at various Stary stages of atherosclerotic lesions (n = 15), we performed endoluminal EIS measurements (n = 147) and validated with histology and immunohistochemistry. We computed the vascular tissue resistance using the equivalent circuit model and normalized the resistance to the lesion-free regions. Tissue resistance was significantly elevated in the oxLDL-rich thin-cap atheromas (1.57±0.40, n = 14, p < 0.001) and fatty streaks (1.36±0.28, n = 33, p < 0.001) as compared with lesion-free region (1.00±0.18, n = 82) or oxLDL-absent fibrous atheromas (0.86±0.30, n = 12). Tissue resistance was also elevated in the calcified core of fibrous atheroma (2.37±0.60, n = 6, p < 0.001). Despite presence of fibrous structures, tissue resistance between ox-LDL-absent fibroatheroma and the lesion-free regions was statistically insignificant (0.86±0.30, n = 12, p > 0.05). Hence, we demonstrate that the application of EIS strategy was sensitive to detect fibrous cap oxLDL-rich lesions and specific to distinguish oxLDL-absent fibroatheroma.
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439)
The complex impedance that would be measured by a fourpoint electrode on the intimal surface of type Va and Vb atherosclerotic lesions was simulated using two different electromagnetic software programs. One program used a nonconformal hexahedral mesh of 2.5 million elements to describe the lesion morphology, whereas the second program used a conformal mesh of 320,000 elements. Even though the nonconformal mesh used more elements, the geometry of the lesion and electrodes was more accurately described by the conformal mesh. The impedance of the lesions was calculated for the frequencies of ½¼ ½¼ ½¼ and ½¼ Hz. The simulated resistance and phase of the lesion for both the nonconformal and conformal mesh were very similar. The small difference in the results can be attributed to the more accurate modeling of the interface between the electrodes and the underlying layer.
Characteristic Impedances Calculations in Arteries with Atherosclerosis Using MAPLE
Abstract—Cardiovascular diseases cause deaths every year. For that reason it is important to model these diseases and the troubles that they can cause into the human body, particularly the arteries, in the cardiovascular field. As an effort for achieving the understanding of the phenomena, an electric analogue representation of the arteries and blood flow has been made, where the key part is the characteristic impedance. We present the calculations made for obtaining the characteristic impedances in different cases.
Procedia Technology, 2013
This paper presents a simulation based study on identification of atherosclerosis in human blood vessels through Electrical Impedance Tomography (EIT) technique. Atherosclerosis is a vital coronary disease in which plaque (a solid substance made of fat, cholesterol, calcium and other substances found in blood) builds up inside the arteries and can lead to serious problems, including heart attack, stroke, or even death. In this work, a non-invasive imaging technique based on the variation of electrical conductivity (and/or relative permittivity) values of the body tissues have been proposed for detection of atherosclerosis. Here, we have modeled the 2D structure of vessels within a closed specified environment. The 2D model is then transformed to 3D platform for analysis. The clots inside the blood vessels have varying electrical conductivities (and/or relative permittivity's) in comparison to that for the blood vessels. Thus, by maintaining a potential difference on the electrodes, which are placed on the body surface, the variation of potential field are obtained along a 2D plane by utilizing the forward solver problem of Electrical Impedance Tomography (EIT). The simulation model and their respective studies are performed in Finite Element Method based Multiphysics Software platform.
Real-Time Electrical Bioimpedance Characterization of Neointimal Tissue for Stent Applications
Sensors (Basel, Switzerland), 2017
To follow up the restenosis in arteries stented during an angioplasty is an important current clinical problem. A new approach to monitor the growth of neointimal tissue inside the stent is proposed on the basis of electrical impedance spectroscopy (EIS) sensors and the oscillation-based test (OBT) circuit technique. A mathematical model was developed to analytically describe the histological composition of the neointima, employing its conductivity and permittivity data. The bioimpedance model was validated against a finite element analysis (FEA) using COMSOL Multiphysics software. A satisfactory correlation between the analytical model and FEA simulation was achieved in most cases, detecting some deviations introduced by the thin "double layer" that separates the neointima and the blood. It is hereby shown how to apply conformal transformations to obtain bioimpedance electrical models for stack-layered tissues over coplanar electrodes. Particularly, this can be applied to...
IEEE Transactions on Biomedical Engineering, 2004
Electrical properties of myocardial tissue are anisotropic due to the complex structure of the myocardial fiber orientation and the distribution of gap junctions. For this reason, measured myocardial impedance may differ depending on the current distribution and direction with respect to myocardial fiber orientation and, consequently, according to the measurement method. The objective of this study is to compare the specific impedance spectra of the myocardium measured using two different methods. One method consisted of transmural measurements using an intracavitary catheter and the other method consisted of nontransmural measurements using a four-needle probe inserted into the epicardium. Using both methods, we provide the in situ specific impedance spectrum (magnitude and phase angle) of normal, ischemic, and infarcted pig myocardium tissue from 1 kHz to 1 MHz. Magnitude spectra showed no significant differences between the measurement techniques. However, the phase angle spectra showed significant differences for normal and ischemic tissues according to the measurement technique. The main difference is encountered after 60 min of acute ischemia in the phase angle spectrum. Healed myocardial tissue showed a small and flat phase angle spectrum in both methods due to the low content of cells in the transmural infarct scar. In conclusion, both transmural and nontransmural measurements of phase angle spectrum allow the differentiation among normal, ischemic, and infarcted tissue.
Myocardial electrical impedance mapping of ischemic sheep hearts and healing aneurysms
Circulation, 1993
BACKGROUND This study was designed to examine the bulk electrical properties of myocardium and their variation with the evolution of infarction after coronary occlusion. These properties may be useful in distinguishing between normal, ischemic, and infarcted tissue on the basis of electrophysiological parameters. METHODS AND RESULTS The electrical impedance of myocardial tissue was studied in a sheep model of infarction. The animal model involved a one-stage ligation of the left anterior descending and second diagonal arteries at a point 40% of the distance from the apex to the base. By use of a four-electrode probe, an epicardial mapping system was developed that allowed for cardiac cycle gated and signal-averaged measurements. Subthreshold current (15 microA) was injected through two of the electrodes at frequencies of 1, 5, and 15 kHz and the induced potential measured with the other two electrodes. Epicardial maps of the left ventricle were obtained during acute infarction and a...
A Quadruple-Sweep Bioimpedance Sensing Method for Arterial Stenosis Detection
IEEE Access, 2023
Current carotid atherosclerosis diagnostic protocols do not feature techniques that would allow for early or frequent medical examinations, leaving a significant number of asymptomatic carotid stenosis cases undetected and often leading to strokes. The key challenge is that current diagnostics are highly operator-dependent. In this work we used idealised biological models to demonstrate a new rapid, potentially inexpensive and operator-independent diagnostic method, aimed at detecting whether a stenosis exists, rather than seeking to be accurately quantifying or localising it. An array of electrodes was used to obtain sequential bioimpedance values over the skin, through a novel scanning technique, covering an area over the artery of interest. FEM simulations, verified through in-vitro experiments on gelatine phantoms, were used to validate the method. The final results, obtained through image processing algorithms, were in the form of planar bio-impedance maps and were successful both in identifying arterial features and detecting the presence of stenoses of different sizes. The results could also be used to indicate the artery's relative orientation to the sensor, eliminating the need for manual alignment by a specialist operator. Therefore, this method shows promise for routine medical examination, either in primary care, or even at home, to indicate whether a patient would require further, more detailed examinations at a specialist clinic.