Open Electrical Impedance Tomography Research Articles

Sodium concentration imaging in dermis layer by square-wave open electrical impedance tomography (SW-oEIT) with spatial voltage thresholding (SVT)

In this study, sodium concentration in the dermis layer is imaged by the square wave open electrical impedance tomography (SW-oEIT) with spatial voltage thresholding (SVT). The SW-oEIT with SVT consists of three steps which are (1) voltage measurement, (2) spatial voltage thresholding, and (3) sodium concentration imaging. In the 1st step, the root mean square voltage is calculated based on the measured voltage under the square wave current through the planar electrodes on the skin domain Ω. In the 2nd step, the m-th measured voltage is converted to a compensated voltage v * based on the voltage electrodes distance and threshold distance in order to highlight the region of interest of the dermis layer In the 3rd step, sodium concentration is imaged by the Gauss-Newton reconstruction method. The SW-oEIT with SVT was applied to multi-layer skin simulation and ex-vivo experiments under various dermis sodium concentrations c in the range of 5–50 mM. As an image evaluation result, the spatial mean conductivity distribution in is successfully determined as increasing c on both simulations and experiments. The relationship between and c was evaluated by the determination coefficient R 2 and the normalized sensitivity The optimized with the highest evaluation values of 0.84 and 0.83 is under the condition of = 2 mm. Based on the signal evaluation, the SW-oEIT with SVT has a 15.32% higher correlation coefficient CC compared to the conventional oEIT based on sinewave injection.

Focusing Sensor Design for Open Electrical Impedance Tomography Based on Shape Conformal Transformation.

Electrical Impedance Tomography (EIT) is a non-invasive detection method to image the conductivity changes inside an observation region by using the electrical measurements at the boundary of this region. In some applications of EIT, the observation domain is infinite and is only accessible from one side, which leads to the so-called open EIT (OEIT) problem. Compared with conventional EIT problems, the observation region in OEIT can only be measured from limited projection directions, which makes high resolution imaging much more challenging. To improve the imaging quality of OEIT, a focusing sensor design strategy is proposed based on shape conformal theory. The conformal bijection is used to map a standard EIT sensor defined at a unit circle to a focusing OEIT sensor defined at an upper half plane. A series of numerical and experimental testes are conducted. Compared with the traditional sensor structure, the proposed focusing sensor has higher spatial resolution at the near-electrode region and is good at distinguishing multi-inclusions which are close to each other.

A Transformation-Domain Image Reconstruction Method for Open Electrical Impedance Tomography Based on Conformal Mapping

Open electrical impedance tomography (OEIT) is a nondestructive testing technique imaging the objects within the infinite observation domain through the electrodes fixed at one side of this domain. A novel image reconstruction method is proposed based on the conformal transformation method. The proposed method solves the EIT problems, including both the forward and inverse problems, in the conformal transform domain, instead of original Euclidean domain. The numerical and experimental results show that the proposed method is with higher computational accuracy for the forward and inverse problems comparing with the traditional methods of truncating the infinite domain to a small closed region. The quantitative analyses show that the proposed method can improve the reconstructed accuracy of OEIT, especially for the conductivity changes far from the electrodes.

Evaluation of measurement and stimulation patterns in open electrical impedance tomography with scanning electrode.

The reconstruction quality in electrical impedance tomography is limited by the current injection amplitude, the injection and measurement patterns, and the measurement accuracy as well as the number and placement of electrodes. This paper dedicates to increase the number of independent voltage measurements by scanning electrode (SE), and design an optimal measurement and stimulation pattern for open electrical impedance tomography (OEIT). Firstly, several measurement patterns are, performed in OEIT, aiming to evaluate the right number of the measurement points for the imaged target in a certain depth. The results indicate that the image quality gets higher with the number of measurement point increased to some extent. Thus, it can guide the optimum design for the electrode system in OEIT. Secondly, through the numerical calculation and salt water tank experiment, in contrast to adjacent current injection pattern, cross-current-injection pattern achieves better reconstruction with higher imaging quality and penetration depth, and is more robust against data noise in deep domain. Lastly, the experiments also indicate that the electrode contact area affects the reconstruction quality and investigation depth. Therefore, OEIT with SE can improve the application in clinic, such as the detection and monitoring of vascular, breast, and pulmonary diseases.

A novel combined regularization algorithm of total variation and Tikhonov regularization for open electrical impedance tomography

A Tikhonov regularization method in the inverse problem of electrical impedance tomography (EIT) often results in a smooth distribution reconstruction, with which we can barely make a clear separation between the inclusions and background. The recently popular total variation (TV) regularization method including the lagged diffusivity (LD) method can sharpen the edges, and is robust to noise in a small convergence region. Therefore, in this paper, we propose a novel regularization method combining the Tikhonov and LD regularization methods. Firstly, we clarify the implementation details of the Tikhonov, LD and combined methods in two-dimensional open EIT by performing the current injection and voltage measurement on one boundary of the imaging object. Next, we introduce a weighted parameter to the Tikhonov regularization method aiming to explore the effect of the weighted parameter on the resolution and quality of reconstruction images with the inclusion at different depths. Then, we analyze the performance of these algorithms with noisy data. Finally, we evaluate the effect of the current injection pattern on reconstruction quality and propose a modified current injection pattern. The results indicate that the combined regularization algorithm with stable convergence is able to improve the reconstruction quality with sharp contrast and more robust to noise in comparison to the Tikhonov and LD regularization methods solely. In addition, the results show that the current injection pattern with a bigger driver angle leads to a better reconstruction quality.

Modeling and simulation of open electrical impedance tomography

In order to reduce the error in image reconstruction caused by changeable positions of the electrodes in Closed Electrical Impedance Tomography (CEIT), an Open EIT (OEIT) model was proposed using fixed electrode array. The problem is assumed to be a virtual field by defining certain local sensitive area instead of solving the boundary problem in the whole electromagnetic field strictly. Modeling and simulation of OEIT have been conducted to determine reasonable boundary parameters and electrode array structure. The image was reconstructed by iterative Newton-Raphson algorithm with Tikhonov and Variation regularization. The experiment results showed that OEIT achieved good resolution and positioning accuracy, and can be applied to distinguish small difference in conductivity of the biological tissues.