KR101576171B1 - Mechanical vibration assisted electrical impedance tomography - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical impedance tomography technique of applying physical vibration to an object and measuring a change in conductivity of an object induced by physical vibration.

Description

[0001] Mechanical vibration assisted electrical impedance tomography [0002]

Electrical Impedance Tomography (EIT), which images the bioimpedance representing the electrical characteristics of living tissue, has been an important research subject of many physicists and mathematicians in relation to the electrophysiological study of the medical field. The conductivity and the permittivity of living tissue vary depending on the molecular level components, the concentration and mobility of ions, the amount and condition of the solvent constituting the body fluid, and the values vary greatly depending on the function and metabolism of the biotissue. Therefore, EIT medical imaging techniques provide totally different useful information that can not be obtained by existing technology, and it enables real-time monitoring of physiological phenomenon using image and imaging of function and metabolism as well as internal structure. In addition, EIT medical imaging techniques are relatively low-cost techniques and can be applied to Young Yu, elderly people and pregnant women because they do not harm tissue, and they can also be used as a long-term observation technique of cell culture.

The existing EIT imaging technique measures the phenomenon that the applied physical quantity is modulated by the corresponding physical properties after applying a low-frequency current to the object in order to restore the distribution of the physical property in the internal section to the image , And a method of extracting the physical properties of the inside of the image from the measured data was mainly used. These methods require reference data before any changes occur in the object, and such reference data may not be obtained. For example, image reconstruction using electrical impedance tomography for the detection of breast cancer tissues or other cancer cells in the body is not provided with reference data (measurement data in the absence of lesions acquired at different time points) Therefore, it is impossible to apply a typical electrical impedance tomography method using time difference data. To overcome this problem, the proposed method is multifrequency electrical impedance tomography using measurement data at various frequencies. However, the EIT is inherently insensitive to changes in conductivity and is sensitive to the geometry of the object being measured. Also, when biological tissue has physical properties such that conductivity and permittivity do not change significantly with frequency, it becomes difficult to apply multifrequency electrical impedance tomography.

*references

1. H. Ammari, O. Kwon, J. K. Seo, and E.J. Woo, T-scan electrical impedance imaging system for anomaly detection, SIAM J. Appl. Math., 65 (2004), 252266.

2. The T-scan technology: electrical impedance as a diagnostic tool for breast cancer detection, Physiol. Meas., 22 (2001), 1-8.

3. H. Benjamin, S. Bhansali, S.B. Hoath, W.L. Pickens, and R. Smallwood, A planar micro-sensor for bio-impedance measurements, Sens. Actuators B: Chemical, 111-112 (2005), 430-435

4. A. Hartov, N. Soni, and A. Halter, Breast cancer screening with electrical impedance tomography electrical impedance tomography: methods, History and Applications, (2005) 167-185

5. E. Lee, Ts. Munkh-Erdene, JK Seo, and EJ Woo, Breast EIT using a new projected image reconstruction method with multi-frequency measurements, Physiological Measurement, 33 (2012), 751.

The electrical impedance tomography technique is to apply a low-frequency current to an object such as a human body, measure the voltage induced by the applied current on the surface, and measure the internal impedance or conductivity and permittivity distribution from the measured data, . This includes the forward problem, which corresponds to the mathematical analysis and modeling of the physical phenomena related to the applied current and the electrical characteristics of the living tissue, and the inverse problem, which is the problem of restoring the distribution of the internal physical properties from the data measured from the surface inverse problem) is needed. As for the mathematical theory of this inverse problem, over the past 30 years, there have been many results of the solution by many mathematicians through micro-local analysis, partial differential equations, and complex analytic theory. However, there are problems in that the quality of the image is deteriorated due to many problems such as fundamental technical difficulties caused by nonlinearity and insensitivity, and modeling errors of a forward model.

The mathematical analysis of the differential equations is necessary to strictly quantify the changes in the internal electrical properties from the measured voltage data after injecting the current from the outside, and it is necessary to improve the understanding of the complex water solution through the harmonic analysis approach. In addition, the use of the fundamental solution of the laplace operator should be maximized to clearly express the link between the changes in internal properties and external measurement data in the form of layer potential. In the present invention, the elasticity equations are analyzed in order to utilize the change of the internal properties through the physical vibration which is not used in the conventional electric impedance tomography. In the present invention, a new impedance tomography technique is devised by organizing these methods and adding a method of applying physical vibration thereto. In the new method, external physical vibration is applied to change the internal conductivity and permittivity, and the difference between the data measured before and after the change is imaged to image the internal conductivity and permittivity distribution diagram.

The present invention deals with an electrical impedance tomography technique for imaging internal electrical properties using both physical vibration, current injection or voltage application, and devices capable of applying such techniques.

In the conventional electrical impedance tomography, when there is no reference data, the reconstructed conductivity image becomes very inaccurate due to modeling error and measurement error. The present invention artificially generates a change in conductivity distribution on a target object using vibration and acquires a difference voltage image before and after the vibration to improve the accuracy of the impedance image.

As can be seen from the reconstructed image, the present invention is a technique for detecting the distribution of internal conductivity and permittivity, which is used in the prior art, has a relatively high resolution and does not require separate reference data as compared with the time difference electrical impedance tomography techniques. In the frequency difference electrical impedance tomography technique used in the prior art, the internal conductivity must vary greatly according to the frequency, but the method of the present invention does not require such a condition. In addition, the current injection or voltage application electrodes and the voltage measurement electrodes can be completely separated to vary the number of electrodes, and the arrangement of the electrodes can be variously configured. Due to these advantages, the method of the present invention can be applied not only to human body but also to various fields such as lipid surveillance and nondestructive inspection, since it can be applied to various objects having electrical properties as well as human body. It is also possible to apply the method of the present invention to a microstructure by reducing the size of the device.

An electrode panel capable of applying a pair or two or more pairs of linearly independent currents, measuring an induced voltage by an injection current, and a device generating a mechanical vibration in the object
As shown in Figs. 1 and 2, the electrode panel and the vibration device are attached to the surface of the object. A mechanical vibration is generated in a target object, a current in two or more directions is applied, and the voltage distribution induced by the injection current is measured in the electrode panel. At this time, the measured voltage changes as the conductivity distribution changes due to the mechanical vibration. The present invention relates to an electrical impedance tomography technique that applies a physical vibration to change the conductivity distribution inside and implements the change of the conductivity distribution according to the vibration using the difference of the voltage data before and after the vibration. In the present invention, the relationship between the change of the conductivity distribution due to the vibration and the voltage data is specified, and an algorithm for imaging the change of the conductivity distribution according to the vibration is developed. The present invention also includes an electrode array of a novel structure that can effectively apply this technique and extract a relatively high resolution image compared to existing electrical impedance tomography techniques.

A pair or two or more pairs of current injecting or voltage applying electrodes are attached to the surface of an object and constant current or constant voltage of several frequencies is applied through them. In the present invention, mechanical vibration is applied at the same time. Various types of voltage measurement electrodes are arranged to measure the induced voltage. For example, you can attach a planar array electrode as shown in the figure below. Measure the voltage at each voltage measuring electrode and transfer the collected data to the computer. The computer extracts images that provide information about internal conductivity and permittivity distribution through image reconstruction algorithm.

Electrical impedance tomography has the disadvantage that it can be measured in real time at low cost compared with MRI or CT, is non-invasive, has good mobility but has low spatial resolution. The apparatus proposed in the present invention has an advantage in that the number of voltage measurement electrodes is increased to increase the amount of collected data to increase the resolution. Further, since the physical vibration is used, it is possible to apply the present invention to a case where no reference data is required and the electrical properties of the object to be measured do not greatly change according to the frequency.

■ Electrical Impedance Tomography Using Physical Vibration

▷ Principle

라고 두고 그 표면을

라 표기하자. 표면에서

만큼의 전류를 주입했을 때 내부영역

에서의 전압

는 The area of the internal conductivity distribution image to extract

And that surface

Let's say. On the surface

When the current is applied to the inner region

The voltage at

The

로 표시한다. 여기에 물리적 진동 g를 외부에서 가하게 되면 내부영역에서의 변위는 아래의 탄성 방정식을 따른다.≪ / RTI > The conductivity is

. Here, when the physical vibration g is externally applied, the displacement in the inner region follows the following elasticity equation.

는 밀도,

는 진동의 주파수,

와

는

의 물성을 특징지어주는 Lame 변수들이다. 물리적 진동을 가하면 내부 변위에 변화가 생기고 이는 내부 도전율의 분포의 변화(

)를 야기하고 이때 다시 표면에서

만큼의 전류를 주입하면 내부영역

에서의 전압(

) 또한 변하여 다음의 식을 만족한다.here

The density,

The frequency of the vibration,

Wow

The

Are the Lame variables that characterize the properties of. When physical vibration is applied, a change occurs in the internal displacement, which is a change in the distribution of internal conductivity

) And then again on the surface

Lt; RTI ID = 0.0 >

The voltage at

) Also, the following equation is satisfied.

는

이며 이는

와 같이 근사된다. 따라서 전압측정 전극에서 수집한 전압 데이터인

와

의 차이를 이용해 내부에서의 도전율 분포를 추출하는 영상을 만들게 된다.Over

The

And

. Therefore, the voltage data collected from the voltage measuring electrode

Wow

The image of the inside conductivity distribution is extracted.

▷ Algorithm

,

을 통하여 전류를 주입하면 서로 독립적인 두 개의 전압이 발생한다. 진동을 가하기 전의 전압들은 (

,

)이고, 진동을 가한 후의 전압들은 (

,

)로 표기한다.- two pairs of current injection electrodes

,

When the current is injected through the electrodes, two independent voltages are generated. The voltages before applying the vibration are (

,

), And the voltages after applying the vibration are (

,

).

Using the relationship

These voltage data satisfy the following equation.

)에서의 전압 데이터를

로 두면 측정 영역으로 투영된

의 값은 간단한 다음의 방정식의 해로 얻어진다.Measuring electrode (

The voltage data

If projected into the measurement area,

Is obtained by the solution of the following simple equation.

, 진동을 가한 후 전압 데이터

를 이용해 우변을 계산하고 아래의 Poisson 방정식을 풀면 투영된 u

의 값을 근사하는

를 얻게 된다.In summary, the voltage data collected before applying the vibration

, Voltage data after applying vibration

The use of calculating the right side and projected by solving the Poisson equation below u

Approximate the value of

.

■ Device structure

This device can reduce the complexity of the device by increasing the number of voltage measurement electrodes by increasing the resolution of the restored image by separating the electrode for applying the current or voltage and the electrode for measuring the voltage. Electrodes for applying linearly independent currents of one pair or more than two pairs are arranged and tens or hundreds of voltage measurement electrodes are disposed therebetween.

■ Numerical Simulation 1

의 투영 이미지를 복원하였다. 아래의 그림은 첫 번째 시뮬레이션에서 사용한 측정방법의 개요와 내부의 도전율 분포이다. In the first numerical simulations, current-fed electrodes were placed at both corners. Using a voltage difference between the time each was applied to physical vibration as above from the left and front side of the inside using the algorithm proposed in this invention u

The projected image of The figure below shows an overview of the measurement method used in the first simulation and the internal conductivity distribution.

When the image restoration algorithm of the present invention is applied to the numerical simulation data, it is possible to restore the following conductivity image. It can be seen that the method of applying vibration affects the quality of the reconstructed image.

■ Numerical Simulation 2

의 투영 이미지를 복원하였다. 아래의 그림은 두 번째 시뮬레이션에서 사용한 측정방법의 개요이다. In the second simulation, the current application electrodes were arranged at four corners. Similarly, by using the voltage difference when each was applied to physical vibration as above from the left and front side of the inside using the algorithm proposed in this invention u

The projected image of The following figure is an overview of the measurement method used in the second simulation.

The reconstructed image below shows that the quality of the reconstructed image is greatly improved by increasing the applied current from one to two.

Ω: object space
λ, μ: Lame variable in the elasticity equation that tells the properties of the object
σ: conductivity distribution
v: voltage
u : position change due to physical vibration

Claims (3)

A voltage is applied to the inside and the surface of the object by applying a current or by applying a voltage to the object while applying physical vibrations that change the conductivity distribution inside the object to various types and sizes of objects having electrical properties including the human body And measuring the induced voltage, and outputting the change of the conductivity distribution according to the vibration inside the object in the form of an image or a signal, using the electrical impedance tomography technique.
It is preferable that a current is injected into the object before or during the application of the physical vibration that changes the conductivity distribution inside the object to various types and sizes of objects having electrical properties including the human body, An electrical impedance tomography technique using vibration to measure a voltage induced on a surface and output a change of a conductivity distribution according to a vibration inside the object in the form of an image or a signal using a difference between the measured induced voltages.
Physical vibration and current injection or the like are applied to the object to measure changes in the conductivity distribution inside the object while applying physical vibrations that change the conductivity distribution inside the object to various types and sizes of objects having electrical properties including the human body Electrical Impedance Tomography Technique Using Vibration Using Simultaneous Physical Vibration and Voltage Application.

Images