1
|
Frerichs I, Händel C, Becher T, Schädler D. Sex differences in chest electrical impedance tomography findings. Physiol Meas 2024; 45:075005. [PMID: 38959902 DOI: 10.1088/1361-6579/ad5ef7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Accepted: 07/03/2024] [Indexed: 07/05/2024]
Abstract
Objective.Electrical impedance tomography (EIT) has been used to determine regional lung ventilation distribution in humans for decades, however, the effect of biological sex on the findings has hardly ever been examined. The aim of our study was to determine if the spatial distribution of ventilation assessed by EIT during quiet breathing was influenced by biological sex.Approach.219 adults with no known acute or chronic lung disease were examined in sitting position with the EIT electrodes placed around the lower chest (6th intercostal space). EIT data were recorded at 33 images/s during quiet breathing for 60 s. Regional tidal impedance variation was calculated in all EIT image pixels and the spatial distribution of the values was determined using the established EIT measures of centre of ventilation in ventrodorsal (CoVvd) and right-to-left direction (CoVrl), the dorsal and right fraction of ventilation, and ventilation defect score.Main results.After exclusion of one subject due to insufficient electrode contact, 218 data sets were analysed (120 men, 98 women) (age: 53 ± 18 vs 50 ± 16 yr (p= 0.2607), body mass index: 26.4 ± 4.0 vs 26.4 ± 6.6 kg m-2(p= 0.9158), mean ± SD). Highly significant differences in ventilation distribution were identified between men and women between the right and left chest sides (CoVrl: 47.0 ± 2.9 vs 48.8 ± 3.3% of chest diameter (p< 0.0001), right fraction of ventilation: 0.573 ± 0.067 vs 0.539 ± 0.071 (p= 0.0004)) and less significant in the ventrodorsal direction (CoVvd: 55.6 ± 4.2 vs 54.5 ± 3.6% of chest diameter (p= 0.0364), dorsal fraction of ventilation: 0.650 ± 0.121 vs 0.625 ± 0.104 (p= 0.1155)). Ventilation defect score higher than one was found in 42.5% of men but only in 16.6% of women.Significance.Biological sex needs to be considered when EIT findings acquired in upright subjects in a rather caudal examination plane are interpreted. Sex differences in chest anatomy and thoracoabdominal mechanics may explain the results.
Collapse
Affiliation(s)
- I Frerichs
- Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein, Campus Kiel, Kiel, Germany
| | - C Händel
- Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein, Campus Kiel, Kiel, Germany
| | - T Becher
- Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein, Campus Kiel, Kiel, Germany
| | - D Schädler
- Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein, Campus Kiel, Kiel, Germany
| |
Collapse
|
2
|
Pennati F, Angelucci A, Morelli L, Bardini S, Barzanti E, Cavallini F, Conelli A, Di Federico G, Paganelli C, Aliverti A. Electrical Impedance Tomography: From the Traditional Design to the Novel Frontier of Wearables. SENSORS (BASEL, SWITZERLAND) 2023; 23:1182. [PMID: 36772222 PMCID: PMC9921522 DOI: 10.3390/s23031182] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 01/16/2023] [Accepted: 01/17/2023] [Indexed: 06/18/2023]
Abstract
Electrical impedance tomography (EIT) is a medical imaging technique based on the injection of a current or voltage pattern through electrodes on the skin of the patient, and on the reconstruction of the internal conductivity distribution from the voltages collected by the electrodes. Compared to other imaging techniques, EIT shows significant advantages: it does not use ionizing radiation, is non-invasive and is characterized by high temporal resolution. Moreover, its low cost and high portability make it suitable for real-time, bedside monitoring. However, EIT is also characterized by some technical limitations that cause poor spatial resolution. The possibility to design wearable devices based on EIT has recently given a boost to this technology. In this paper we reviewed EIT physical principles, hardware design and major clinical applications, from the classical to a wearable setup. A wireless and wearable EIT system seems a promising frontier of this technology, as it can both facilitate making clinical measurements and open novel scenarios to EIT systems, such as home monitoring.
Collapse
Affiliation(s)
| | - Alessandra Angelucci
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, 20133 Milan, Italy
| | | | | | | | | | | | | | | | | |
Collapse
|
3
|
Kozłowska N, Wierzbicka M, Jasiński T, Domino M. Advances in the Diagnosis of Equine Respiratory Diseases: A Review of Novel Imaging and Functional Techniques. Animals (Basel) 2022; 12:381. [PMID: 35158704 PMCID: PMC8833607 DOI: 10.3390/ani12030381] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 02/02/2022] [Accepted: 02/03/2022] [Indexed: 02/04/2023] Open
Abstract
The horse, as a flight animal with a survival strategy involving rapid escape from predators, is a natural-born athlete with enormous functional plasticity of the respiratory system. Any respiratory dysfunction can cause a decline in ventilation and gas exchange. Therefore, respiratory diseases often lead to exercise intolerance and poor performance. This is one of the most frequent problems encountered by equine internists. Routine techniques used to evaluate respiratory tract diseases include clinical examination, endoscopic examination, radiographic and ultrasonographic imaging, cytological evaluation, and bacterial culture of respiratory secretions. New diagnostic challenges and the growing development of equine medicine has led to the implementation of advanced diagnostic techniques successfully used in human medicine. Among them, the use of computed tomography (CT) and magnetic resonance (MR) imaging significantly broadened the possibilities of anatomical imaging, especially in the diagnosis of upper respiratory tract diseases. Moreover, the implementation of spirometry, electrical impedance tomography (EIT), and impulse oscillation system (IOS) sheds new light on functional diagnostics of respiratory tract diseases, especially those affecting the lower part. Therefore, this review aimed to familiarize the clinicians with the advantages and disadvantages of the advanced diagnostic techniques of the equine respiratory tract and introduce their recent clinical applications in equine medicine.
Collapse
Affiliation(s)
| | - Małgorzata Wierzbicka
- Department of Large Animal Diseases and Clinic, Institute of Veterinary Medicine, Warsaw University of Life Sciences, 02-787 Warsaw, Poland; (N.K.); (T.J.)
| | | | - Małgorzata Domino
- Department of Large Animal Diseases and Clinic, Institute of Veterinary Medicine, Warsaw University of Life Sciences, 02-787 Warsaw, Poland; (N.K.); (T.J.)
| |
Collapse
|
4
|
|
5
|
Cambiaghi B, Moerer O, Kunze-Szikszay N, Mauri T, Just A, Dittmar J, Hahn G. A spiky pattern in the course of electrical thoracic impedance as a very early sign of a developing pneumothorax. Clin Physiol Funct Imaging 2016; 38:158-162. [PMID: 27619316 DOI: 10.1111/cpf.12385] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 07/11/2016] [Indexed: 11/29/2022]
Abstract
A pneumothorax (PTX) is a potentially lethal condition in high-risk intensive care patients. Electrical impedance tomography (EIT) has been proven to detect PTX at the bedside. A so far not described pattern in the course of thoracic impedance at an early state of PTX was observed in a pig model of ventilator-induced lung injury (VILI) used for a more extensive study. EIT was performed at a framerate of 50 Hz. Beginning of PTX at normal ventilation, manifestation of PTX at VILI ventilation (plateau pressure 42 cm H2 O) and final pleural drainage were documented. At ventilation with 8·6 ml kg-1 , early PTX findings prior to any clinical deterioration consisted in a spike-like pattern in the time course of impedance (relative impedance change referred to initial end-expiratory level). Spike amplitudes (mean ± SD) were the following: 0·154 ± 0·059 (right lung) and 0·048 ± 0·050 (left lung). At this state, end-expiratory levels (mean ± SD) were still similar, -0·035 ± 0·010 (right) and -0·058 ± 0·022 (left). After application of VILI ventilation (38 ml kg-1 ), a PTX developed slowly, being confirmed by a continuous increase in the end-expiratory level on the right side and diverging levels of +0·320 ± 0·057 (right) and -0·193 ± 0·147 (left) at full manifestation. We assume that spikes reflect a temporary change in the electrical pathway caused by leakage into the pleural cavity. This newly described phenomenon of spikes is considered to be a potentially useful indicator for a very early detection of an evolving PTX in high-risk ICU patients.
Collapse
Affiliation(s)
- B Cambiaghi
- Dipartimento di Medicina e Chirurgia, Università Degli Studi Milano-Bicocca, Monza (MB), Italy
| | - O Moerer
- Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany
| | - N Kunze-Szikszay
- Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany
| | - T Mauri
- Department of Anesthesiology, Intensive Care and Emergency Medicine IRCCS Ca' Granda Foundation, Hospital Maggiore Policlinico di Milano, Milan, Italy
| | - A Just
- Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany
| | - J Dittmar
- Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany
| | - G Hahn
- Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany
| |
Collapse
|
6
|
Li N, Xu H, Zhou Z, Xin J, Sun Z, Xu X. Reconfigurable bioimpedance emulation system for electrical impedance tomography system validation. IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS 2013; 7:460-468. [PMID: 23893205 DOI: 10.1109/tbcas.2012.2224110] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This paper presents a novel bioimpedance emulation method designed for electrical impedance tomography system validation. The proposed method can emulate the impedance frequency characteristics of various biological samples from user configurations. The bioimpedance emulation system is realized in a hardware prototype comprising current sensing circuitry, voltage generating circuitry, a USB controller and a field-programmable gate array (FPGA) for reconfigurable digital control of emulated impedance. Experimental validation shows that the emulation system exhibits good accuracy ( > 97% at 1 kOhm magnitude) in the frequency range 1 kHz to 1 MHz. The digitally configurability offers advantages in flexibility, repeatability, and cost-efficient compared to more traditional approaches, simplifying the validation process of electrical impedance tomography systems.
Collapse
Affiliation(s)
- Nan Li
- College of Electronic Science and Engineering, National University of Defense Technology, 410073 Changsha, China.
| | | | | | | | | | | |
Collapse
|
7
|
Hashemzadeh P, Kantartzis P, Zifan A, Liatsis P, Nordebo S, Bayford R. A fisher information matrix interpretation of the NOSER algorithm in electrical impedance tomography. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2010; 2010:5000-5. [PMID: 21096682 DOI: 10.1109/iembs.2010.5627208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In this paper, we employ the concept of the Fisher information matrix (FIM) to reformulate and improve on the "Newton's One-Step Error Reconstructor" (NOSER) algorithm. FIM is a systematic approach for incorporating statistical properties of noise, modeling errors and multi-frequency data. The method is discussed in a maximum likelihood estimator (MLE) setting. The ill-posedness of the inverse problem is mitigated by means of a nonlinear regularization strategy. It is shown that the overall approach reduces to the maximum a posteriori estimator (MAP) with the prior (conductivity vector) described by a multivariate normal distribution. The covariance matrix of the prior is a diagonal matrix and is computed directly from the Fisher information matrix. An eigenvalue analysis is presented, revealing the advantages of using this prior to a Gaussian smoothness prior (Laplace). Reconstructions are shown using measured data obtained from a shallow breathing of an adult human subject. The reconstructions show that the FIM approach clearly improves on the original NOSER algorithm.
Collapse
Affiliation(s)
- Parham Hashemzadeh
- Department of Health and Social Sciences, Middlesex University, London NW44BT, United Kingdom.
| | | | | | | | | | | |
Collapse
|
8
|
Dai T, Gómez-Laberge C, Adler A. Reconstruction of conductivity changes and electrode movements based on EIT temporal sequences. Physiol Meas 2008; 29:S77-88. [PMID: 18544802 DOI: 10.1088/0967-3334/29/6/s07] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Electrical impedance tomography (EIT) reconstructs a conductivity change image within a body from electrical measurements on the body surface; while it has relatively low spatial resolution, it has a high temporal resolution. One key difficulty with EIT measurements is due to the movement and position uncertainty of the electrodes, especially due to breathing and posture change. In this paper, we develop an approach to reconstruct both the conductivity change image and the electrode movements from the temporal sequence of EIT measurements. Since both the conductivity change and electrode movement are slow with respect to the data frame rate, there are significant temporal correlations which we formulate as priors for the regularized image reconstruction model. Image reconstruction is posed in terms of a regularization matrix and a Jacobian matrix which are augmented for the conductivity change and electrode movement, and then further augmented to concatenate the d previous and future frames. Results are shown for simulation, phantom and human data, and show that the proposed algorithm yields improved resolution and noise performance in comparison to a conventional one-step reconstruction method.
Collapse
Affiliation(s)
- Tao Dai
- Systems and Computer Engineering, Carleton University, Ottawa, Canada
| | | | | |
Collapse
|
9
|
Baker AB, McLeod CN, Roxburgh AJ, Bannister P. Descending Aortic Flow Contribution to Intrathoracic Impedance—Development and Preliminary Testing of a Dual Impedance Model. J Clin Monit Comput 2008; 22:11-22. [DOI: 10.1007/s10877-007-9102-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2007] [Accepted: 10/22/2007] [Indexed: 11/27/2022]
|
10
|
Assessment of electrical impedance endotomography for hardware specification. Biomed Imaging Interv J 2006; 2:e24. [PMID: 21614229 PMCID: PMC3097623 DOI: 10.2349/biij.2.2.e24] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Revised: 01/13/2006] [Accepted: 03/28/2006] [Indexed: 11/17/2022] Open
Abstract
PURPOSE The purpose of the study is the quantitative assessment of Electrical Impedance Endotomography (EIE) for the specification of hardware systems. EIE is a modality of Electrical Impedance Tomography (EIT) where the electrodes are located on a probe placed in the middle of the region of interest. The absence of material boundary to the explored volume and the decrease in sensitivity away from the probe requires specific study. MATERIAL AND METHODS The method is the derivation of the equation linking explored medium's conductivity, the sensitivity distribution of the electrode patterns used for data collection and measuring system's noise and bandwidth. The assessment of EIE was achieved by means of simulations based on realistic data of conductivity and noise level. RESULTS The derived equation enabled the estimation of the current needed under realistic operating conditions corresponding to prostate imaging. The generalisation to other organs is straightforward. The image reconstructed from the simulated data and from bench experiments were in agreement and showed that the two selected drive patterns, fan3 and adjacent, gave images of similar quality in absence of noise and that adjacent drive requires significantly higher measurement current. CONCLUSION The study confirmed the feasibility of EIE with achievable hardware specifications. The derived equation enabled the determination of design parameters for the specification of hardware systems corresponding to any given application. The study also showed that EIE is more appropriate for tissue characterisation than for high speed imaging.
Collapse
|
11
|
Fournier-Desseux A, Jossinet J. Assessment of 1-lead and 2-lead electrode patterns in electrical impedance endotomography. Physiol Meas 2005; 26:337-49. [PMID: 15886430 DOI: 10.1088/0967-3334/26/4/001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Electrical impedance endotomography (EIE) is a modality of impedance imaging where the electrodes are located on an insulating core placed at the centre of the region of interest. The absence of a physical limit to the medium surrounding the probe enables the use of remote electrodes. The present study compares the features of 2-lead measurements, where the two pairs of electrodes are located on the probe, to 1-lead measurements, where one of the two injection electrodes and one of the two sensing electrodes are located at a distance far away from the probe. The methodology was the characterization of the sensitivity matrix under the influence of electrode pattern, reconstruction radius and mesh construction. Three mesh constructions, three values of the reconstruction radius and five electrode patterns were compared. The study was carried out in 2D using calculated data. Measurement noise was simulated by an addition of 5% Gaussian white noise. The images were reconstructed using the Tikhonov method and L-curve technique. The results show that the reconstruction mesh and the radius of the reconstruction domain have less influence on the conditioning of the sensitivity matrix than the electrode pattern. Both 1-lead and 2-lead configurations enabled the reconstruction of images of relatively similar quality. Additional selection criteria are expected from hardware considerations.
Collapse
Affiliation(s)
- Anne Fournier-Desseux
- Research Laboratory U556, National Institute of Health and Medical Research, INSERM, 151 Cours Albert Thomas, 69424 Lyon Cedex 03, France.
| | | |
Collapse
|
12
|
Victorino JA, Borges JB, Okamoto VN, Matos GFJ, Tucci MR, Caramez MPR, Tanaka H, Sipmann FS, Santos DCB, Barbas CSV, Carvalho CRR, Amato MBP. Imbalances in Regional Lung Ventilation. Am J Respir Crit Care Med 2004; 169:791-800. [PMID: 14693669 DOI: 10.1164/rccm.200301-133oc] [Citation(s) in RCA: 347] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Imbalances in regional lung ventilation, with gravity-dependent collapse and overdistention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation. Multiple scans with both devices were collected during slow-inflation breaths. Six repeated breaths were monitored by impedance tomography, showing acceptable reproducibility. We observed acceptable agreement between both technologies in detecting right-left ventilation imbalances (bias = 0% and limits of agreement = -10 to +10%). Relative distribution of ventilation into regions or layers representing one-fourth of the thoracic section could also be assessed with good precision. Depending on electrode positioning, impedance tomography slightly overestimated ventilation imbalances along gravitational axis. Ventilation was gravitationally dependent in all patients, with some transient blockages in dependent regions synchronously detected by both scanning techniques. Among variables derived from computerized tomography, changes in absolute air content best explained the integral of impedance changes inside regions of interest (r(2) > or = 0.92). Impedance tomography can reliably assess ventilation distribution during mechanical ventilation.
Collapse
Affiliation(s)
- Josué A Victorino
- Respiratory ICU, Hospital das Clinicas, Pulmonary Department, Univerisity of São Paulo, São Paulo, Brazil
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
West RM, Aykroyd RG, Meng S, Williams RA. Markov chain Monte Carlo techniques and spatial–temporal modelling for medical EIT. Physiol Meas 2004; 25:181-94. [PMID: 15005315 DOI: 10.1088/0967-3334/25/1/025] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Many imaging problems such as imaging with electrical impedance tomography (EIT) can be shown to be inverse problems: that is either there is no unique solution or the solution does not depend continuously on the data. As a consequence solution of inverse problems based on measured data alone is unstable, particularly if the mapping between the solution distribution and the measurements is also nonlinear as in EIT. To deliver a practical stable solution, it is necessary to make considerable use of prior information or regularization techniques. The role of a Bayesian approach is therefore of fundamental importance, especially when coupled with Markov chain Monte Carlo (MCMC) sampling to provide information about solution behaviour. Spatial smoothing is a commonly used approach to regularization. In the human thorax EIT example considered here nonlinearity increases the difficulty of imaging, using only boundary data, leading to reconstructions which are often rather too smooth. In particular, in medical imaging the resistivity distribution usually contains substantial jumps at the boundaries of different anatomical regions. With spatial smoothing these boundaries can be masked by blurring. This paper focuses on the medical application of EIT to monitor lung and cardiac function and uses explicit geometric information regarding anatomical structure and incorporates temporal correlation. Some simple properties are assumed known, or at least reliably estimated from separate studies, whereas others are estimated from the voltage measurements. This structural formulation will also allow direct estimation of clinically important quantities, such as ejection fraction and residual capacity, along with assessment of precision.
Collapse
Affiliation(s)
- Robert M West
- Nuffield Institute for Health, University of Leeds, Leeds LS2 9PL, UK
| | | | | | | |
Collapse
|
14
|
Vauhkonen PJ, Vauhkonen M, Kaipio JP. Errors due to the truncation of the computational domain in static three-dimensional electrical impedance tomography. Physiol Meas 2000; 21:125-35. [PMID: 10720008 DOI: 10.1088/0967-3334/21/1/316] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In electrical impedance tomography (EIT), an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. The currents spread out in three dimensions and therefore off-plane structures have a significant effect on the reconstructed images. A question arises: how far from the current carrying electrodes should the discretized model of the object be extended? If the model is truncated too near the electrodes, errors are produced in the reconstructed images. On the other hand if the model is extended very far from the electrodes the computational time may become too long in practice. In this paper the model truncation problem is studied with the extended finite element method. Forward solutions obtained using so-called infinite elements, long finite elements and separable long finite elements are compared to the correct solution. The effects of the truncation of the computational domain on the reconstructed images are also discussed and results from the three-dimensional (3D) sensitivity analysis are given. We show that if the finite element method with ordinary elements is used in static 3D EIT, the dimension of the problem can become fairly large if the errors associated with the domain truncation are to be avoided.
Collapse
Affiliation(s)
- P J Vauhkonen
- Department of Applied Physics, University of Kuopio, Finland
| | | | | |
Collapse
|
15
|
Abstract
Pathophysiological events in biological tissue are characterized by a shift in electrical impedance spectra of the tissue under study. In this paper, techniques based on electrical impedance are reviewed with emphasis on their possible role in evaluating the skin reactivity of an individual, including results from impedance measurement studies on patients with allergic contact reactions, wheals, tuberculin tests, and irritant contact reactions and on an appropriate number of controls. The results show that, compared to relevant controls, at different types of experimental cutaneous reactions, both of allergic and irritant type, statistically significant changes of the impedance parameters have been detected. Each reaction type had a specific impedance index pattern. Data up to now indicate that the improved impedance technique offers not only a noninvasive alternative for characterization and perhaps differentiation between the skin responses induced by either an allergen or an irritant, but also a capability to distinguish responses induced by chemically different irritants.
Collapse
Affiliation(s)
- M Nyrén
- Department of Dermatology and Venereology, Karolinska Institute, Huddinge University Hospital, Sweden
| | | | | |
Collapse
|
16
|
Brown BH, Flewelling R, Griffiths H, Harris ND, Leathard AD, Lu L, Morice AH, Neufeld GR, Nopp P, Wang W. EITS changes following oleic acid induced lung water. Physiol Meas 1996; 17 Suppl 4A:A117-30. [PMID: 9001610 DOI: 10.1088/0967-3334/17/4a/016] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We present the results of using electrical impedance tomographic spectroscopy (EITS) to follow the changes in lung water induced by oleic acid. Measurements were made on three goats before and after the injection of oleic acid. In addition to the EITs measurements, lung water was also measured using a double-indicator technique. Large falls in lung electrical impedance were seen as a result of the increase in lung water but the size of the fall was a function of the frequency at which the measurements were made. These changes have been modelled using the Cole equation. Four-electrode measurements were also made on two extracted porcine lungs and Cole equation modelling carried out following the introduction of saline into the lungs. Results were similar in the two sets of animal experiments.
Collapse
Affiliation(s)
- B H Brown
- Department of Medical Physics, Royal Hallamshire Hospital, Sheffield, UK
| | | | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Metherall P, Barber DC, Smallwood RH, Brown BH. Three-dimensional electrical impedance tomography. Nature 1996; 380:509-12. [PMID: 8606768 DOI: 10.1038/380509a0] [Citation(s) in RCA: 203] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The electrical resistivity of mammalian tissues varies widely and is correlated with physiological function. Electrical impedance tomography (EIT) can be used to probe such variations in vivo, and offers a non-invasive means of imaging the internal conductivity distribution of the human body. But the computational complexity of EIT has severe practical limitations, and previous work has been restricted to considering image reconstruction as an essentially two-dimensional problem. This simplification can limit significantly the imaging capabilities of EIT, as the electric currents used to determine the conductivity variations will not in general be confined to a two-dimensional plane. A few studies have attempted three-dimensional EIT image reconstruction, but have not yet succeeded in generating images of a quality suitable for clinical applications. Here we report the development of a three-dimensional EIT system with greatly improved imaging capabilities, which combines our 64-electrode data-collection apparatus with customized matrix inversion techniques. Our results demonstrate the practical potential of EIT for clinical applications, such as lung or brain imaging and diagnostic screening.
Collapse
Affiliation(s)
- P Metherall
- Department of Medical Physics and Clinical Engineering, University of Sheffield, UK
| | | | | | | |
Collapse
|
18
|
Meeson S, Killingback AL, Blott BH. The dependence of EIT images on the assumed initial conductivity distribution: a study of pelvic imaging. Phys Med Biol 1995; 40:643-57. [PMID: 7610119 DOI: 10.1088/0031-9155/40/4/010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
EIT measurements on humans are often made in regions of the body where the conductivity distribution is far from uniform. This paper addresses the problem of deriving accurate quantitative data in one such region: the conductivity changes associated with the accumulation of blood in the pelvic bowl. A computer map of the bone in the pelvic region was constructed, from which an appropriate reconstruction matrix was generated. Both computer simulations and tank tests were performed to assess whether this bone reconstruction matrix produced impedance images with closer fidelity to the measured object than images produced using a reconstruction based on a uniform conductivity distribution. As expected, images produced by the computer simulation indicated that the bone reconstruction matrix produced images of better fidelity than did the uniform reconstruction matrix. However, in the case of the tank data only a moderate improvement was achieved. The reconstruction matrix based on a uniform conductivity distribution was found to produce satisfactory images for both bone and near-uniform objects, but for regions further into the pelvic bowl, where the signal was lower, the uniform reconstruction matrix was less satisfactory.
Collapse
Affiliation(s)
- S Meeson
- Department of Physics, University of Southampton, UK
| | | | | |
Collapse
|