Biomedical subjects

Xiuzhen Dong

Publications and source records attributed to Xiuzhen Dong.

18 recordsLinked to original sources

PubMed2006

Pseudo-polar drive patterns for brain electrical impedance tomography.

Brain electrical impedance tomography (EIT) is a difficult task as brain tissues are enclosed by the skull of high resistance and cerebrospinal fluid (CSF) of low resistance, which makes internal resistivity information more difficult to extract. In order to seek a single source drive pattern that is more suitable for brain EIT, we built a more realistic experimental setting that simulates a head with the resistivity of the scalp, skull, CSF and brain, and compared the performance of adjacent, cross, polar and pseudo-polar drive patterns in terms of the boundary voltage dynamic range, independent measurement number, total boundary voltage changes and anti-noise performance based on it. The results demonstrate that the pseudo-polar drive pattern is optimal in all the aspects except for the dynamic range. The polar and cross drive patterns come next, and the adjacent drive pattern is the worst. Therefore, the pseudo-polar drive pattern should be chosen for brain EIT.

Brain↗

PubMed2006

[Antigen-antibody reaction model of solid-phase surface and active biochip system].

To overcome the present limitations of passive biochip, based on the basic principle of antigen-antibody reaction, we develop an antigen-antibody reaction model of solid-phase surface and design a novel active biochip system according to this model, which introduces the negative pressure and controlling devices to control the immunoreactions on the nitrocellulose (NC) membrane. From the computer simulation results, this is a rapid, stable, robust and practicable system, which can be used to increase the efficiency of immunoreactions and improve the reproducibility and accuracy of biochip analysis.

Antigen-Antibody Reactions↗

PubMed2005

Design and simulation of active biochip system.

To solve the problems existing in passive biochip systems, we designed a novel active biochip system. This system introduces negative pressure and controlling devices to adjust the antigen-antibody reaction on the nitrocellulose membrane. Computational simulation demonstrated that this system is a rapid, stable, robust and practical system that may enhance the efficiency of antigen-antibody reactions and improve the repeatability and accuracy of biochip analysis.

Antigen-Antibody Complex↗

PubMed2005

[A method of building the finite-element model with the contour line of human brain].

The contour line of human brain was simulated by the curve-fitting methods and then the inner area was discretized by advancing-front methods which was improved at last. The curve-fitting result was similar to the CT picture of the human brain and the discrete result of inner area could be completed quickly by improved advanced-front methods. A finite element model with the contour line of human brain was built primarily which will contribute to the next algorithm study of electrical impedance tomography in human brain.

Algorithms↗

PubMed2005

[A data acquisition system for induced current electrical impedance tomography].

Induced current electrical impedance tomography (ICEIT) is a new branch of electrical impedance tomography (EIT). We have designed and set up a high accuracy ICEIT hardware system with 32 electrodes based on physical phantom, and we have brought forward a new method to reduce the additive electromotive force (EMF) in circuit of the electrode leads. By use of the technique of twisted pair wire, the additive EMF in the circuit of the electrode leads has been reduced to 10% of that before use and the precision of the system has been improved. The precision of the final results is better than 0.5% after 1000 measurement data averaged. Applying the reconstructive algorithm, we have obtained preliminary images based on physical phantom.

Algorithms↗

PubMed2005

[A bipolar optocoupler isolation amplifier with high precision and wide bandwidth].

To fit the technological requirements in electrical impedance tomography system, an improved bipolar optocoupler isolation amplifier based on single analog optocoupler was realized. The experimental results illustrates that the full power -3dB bandwidth of this circuit is greater than 800 KHz, the equivalent output noise is lower than 50 uV(RMS), and the linearity at +/- 4 V inputs is lower than 0.01%. In addition to these features, the circuit also have the advantages of simple structure and no distortion caused by mismatch between analog optocouplers.

Amplifiers, Electronic↗

PubMed2005

[Frequency characteristic of diseased breast tissues detected by electrical impedance scanning].

The rules of conductance parameters on diseased breast tissue, which change with the driven frequency, are studied by use of electrical impedance scanning. This work is intended to provide a basis for further examination of breast. We have obtained conductance parameters' frequency characteristic of three kinds of breast diseases, i.e. invasive ductal carcinoma, neoplastic hyperplasia, and mastopathia. And by comparison, we find that the frequency characteristic of the diseased breast tissues is different from that of the peripheral normal tissues, and the frequency characteristic shows differences among the three kinds of diseased breast tissues. So, we are able to identify the kind of breast disease by its frequency characteristic.

Breast Diseases↗

PubMed2004

[An experimental system of induced-current EIT].

Induced-current electrical impedance tomography (ICEIT) is a newly hot research field in electrical impedance tomography (EIT) because of its advantages of contactless exciting. A preliminary ICEIT system with 3 excitation coils has been accomplished. It includes the constant current source (CCS), power amplifiers, excitation coils,physical phantom, measurement-mode setting circuit, signal measuring block, DAC and digital I/O card. The CCS is accomplished with Direct Digital Synthesis (DDS) technique. Its frequency is 46.875 KHz. Its output current is divided into 16 steps from 0.16 mA to 2.56 mA which can be set by computer. The three driving coils have the same diameter of 50 cm, each coil's inductance is 193.5 microH. The power amplifier can provide 800 mA driving current (f = 46.875 KHz) to the coil under +/- 25 V power supplying. The signal from measurement electrodes is switched to measurement channel which includes IA, BP filter and synchronized demodulator, then the analog signal is converted to digital signal by a 12b A/D Card and the data is acquired by DMA mode. Our experiments show that a distinguish change of signal from the surface electrodes can be acquired by the experimental system when different objects are placed in the physical phantom. And 3 x 31 signals for preliminary imaging have been acquired.

Algorithms↗

PubMed2004

[On excellent education mode of biomedical engineering in USA].

Based on the rankings of the best undergraduate/graduate biomedical engineering programs from the USA News & World Report, we have made a comprehensive analysis on the excellent education mode in USA 2002. It is hoped that the results as reference materials will be useful to our biomedical education at home.

Biomedical Engineering↗

PubMed2004

[The measurement frequency distribution in tissue impedance spectroscopy measurement].

In the research of tissue impedance spectroscopy measurement, the authors constructed a frequency sets that produce angularly equidistant points on the Nyquist loci. The studies of simulation data model demonstrate that, by use of the same quantity of frequency points and in comparison with the frequency sets that are logarithmic and quasi-linear, the angularly equidistant frequency sets can improve the estimate accuracy of tissue electrical model parameters of alpha and fc.

Biomedical Engineering↗

PubMed2003

[In vivo measurement of rabbits brain impedance frequency response and the elementary imaging of EIT].

The in vivo measurements of rabbit brain tissue impedance were taken under both normal and ischemic conditions by using two-electrode measurement method in the frequency range from 0.1 Hz to 1 MHz. The dynamic images about the resistivity of cerebral ischemia were reconstructed based on a 16-electrode system. The results of in vivo measurement showed that the ratio of impedance increased can be as high as 75% at frequencies lower than 10 Hz. In the range from 1 KHz to 1 MHz, the ratio showed a constant value of 15%. The electrical impedance tomography (EIT) images obtained suggested that the regions of impedance changes highly correspond to the position of ischemia. It is confirmed that the brain function changes caused by local deficiency of blood can be detected and imaged by EIT method.

Animals↗

PubMed2003

[The complex impedance frequency response and the equivalent circuit model of human brain].

The complex impedance measurements of human brain tissue in vitro are made by using four-electrode measurement methods in the frequency range from 0.1 Hz to 1 MHz. The Solartron 1255 B frequency response analyzer is used. The frequency response curves of the imaginary part of human brain's complex impedance do not appear as a single peak curve which other bio-tissues show, and the Cole-Cole diagram of human brain is different from the others as well. The construction of the equivalent circuit model obtained is more complex. However, these characteristics of human brain are all the same as rabbit brain's. The equivalent circuit model obtained will be helpful to constructing the equivalent circuit model of human head in the EIT researches.

Adult↗

PubMed2003

[Nonlinear analysis on the EEG information of rat epileptic model].

The aim of this study was to develop a new method of epileptic prediction using nonlinear dynamic theory. When rat was falling sickness, its EEG was researched by using approximate entropy and correlation dimension. The results showed the approximate entropy and correlation dimension during epileptic seizure are obviously lower than those before seizure and after seizure. The span of time before seizure is a special phase. Before the seizure symptom appeared, the complexity of EEG had begun declining. Thus, the outbreak of epilepsy could be predicted in short time using nonlinear dynamic methods.

Algorithms↗

PubMed2002

The number of electrodes and basis functions in EIT image reconstruction.

In electrical impedance tomography, many factors affect the image reconstruction results. Among them are the number of electrodes (NOE) and the number of conductivity basis functions (NOCBF) for image reconstruction. The NOCBF generally reflects the density of the mesh with which images are reconstructed. How and to what extent do these factors affect the image reconstruction and corresponding images? In this area detailed analysis is still lacking. This study aims to address the above question. In this study, image reconstruction and its ill-posed condition were analysed by singular value decomposition (SVD) and spectral expansion theory with different configurations of NOE and NOCBF. The results in this study indicate that for a circular 2D plane object with electrodes evenly located around the boundary: (1) Under certain conditions, increasing the NOE enables us to improve the ill-posed condition in image reconstruction and hence improve the image quality. Generally more improvement is expected near the image periphery than in the image centre. (2) Increasing the NOCBF generally worsens the ill-posed condition. But it enables the solution to be sought in a finer subspace and may be able to improve the image quality on the periphery, while generally the result in image centre depends more on the prior information incorporated in the regularization.

Algorithms↗

PubMed2002

Effects of incompatible boundary information in EIT on the convergence behavior of an iterative algorithm.

In electrical impedance tomography, currents are applied to the body through electrodes that are attached to the surface and the corresponding surface voltages are measured. Based on these boundary measurements, the internal admittivity distribution of the body can be reconstructed. In order to improve the image quality it is necessary and useful to apply physiologically meaningful prior information into the image reconstruction. Such prior information usually can be obtained from other sources. For example, information on the object's boundary shape and internal structure can be obtained from computed tomography and magnetic resonance imaging scan. However, this type of prior information may change from time to time and from person to person. As these changes are limited anatomically and physiologically, the prior information including the possible changes can be presented in a number of variational forms. The aim of this paper is to find which form of prior information is more compatible for a specific imaged object at the time of imaging. This paper proposes a new method for selecting the most appropriate form of prior information, through the procedure of iterative image reconstruction by using the information obtained from boundary measurements. The method is based on the principle that incompatible prior information causes errors which are able to affect the image reconstruction's convergence behavior. In this method, according to the various forms of prior information available, several image reconstruction configurations are designed. Then, through monitoring the convergence behavior in an iterative image reconstruction, the configuration with compatible prior information can be found among those different configurations. As an example, the prior information regarding the imaged object's boundary shape and internal structure was studied by computer simulation. Results were shown and discussed.

Algorithms↗

PubMed2002

[Simulation study of Kubicek formula for cardiac stroke volume calculation by 3-dimensional finite element method].

This paper deals with the clinical application value of Kubicek formula for cardiac stroke volume calculation from the angle of Kubicek model simulation by 3-dimensional finite element method. In the process of computer simulation, we have made a comparison between the result of model simulation, the specific value of Kubicek formula for cardiac stroke volume calculation, and the theoretical value of the prescribed model. The simulation results showed that an approximately linear relationship exists between the impedance change and the blood volume change of the aorta in the model, which has proved that Kubicek formula for cardiac stroke volume calculation has great clinical application value. On the other hand, the new method has opened up a path for studying the basic theory of impedance cardiography.

Algorithms↗

PubMed2002

[Simulation study of the reconstruction algorithm for electrical impedance tomography based on the sensitivity theorem].

It is the intent of this paper to develop better reconstruction algorithm for electrical impedance tomography (EIT). Simulation study of the reconstruction algorithm based on the sensitivity theorem is made and the reconstruction algorithm is compared with other normal algorithms. The results indicate that sensitivity method as a kind of static reconstruction algorithm has higher accuracy and speed of iteration, so it is worth researching for laboratory modality work.

Algorithms↗

PubMed2002

[The impedance frequency response of the human skull].

The human skull impedance was quantitatively measured by means of Frequency Response Analyzer and its software. The impedance-frequency response curves of human skull were obtained. By analyzing the curves, we found that the characteristic frequency of human skull should be around 10 KHz.

Adult↗