A multifrequency time-difference electrical impedance tomography algorithm using spectral constraints / 生物医学工程学杂志

This study aims to propose a multifrequency time-difference algorithm using spectral constraints. Based on the knowledge of tissue spectrum in the imaging domain, the fraction model was used in conjunction with the finite element method (FEM) to approximate a conductivity distribution. Then a frequency independent parameter (volume or area fraction change) was reconstructed which made it possible to simultaneously employ multifrequency time-difference boundary voltage data and then reduce the degrees of freedom of the reconstruction problem. Furthermore, this will alleviate the illness of the EIT inverse problem and lead to a better reconstruction result. The numerical validation results suggested that the proposed time-difference fraction reconstruction algorithm behaved better than traditional damped least squares algorithm (DLS) especially in the noise suppression capability. Moreover, under the condition of low signal-to-noise ratio, the proposed algorithm had a more obvious advantage in reconstructions of targets shape and position. This algorithm provides an efficient way to simultaneously utilize multifrequency measurement data for time-difference EIT, and leads to a more accurate reconstruction result. It may show us a new direction for the development of time-difference EIT algorithms in the case that the tissue spectrums are known.

Individualized teaching mode in course of Digital Signal Processing / 医疗卫生装备

The communication between the students and the teacher was introduced from three aspects of foregone course, communication channel as well as homework and experiment. The individualized teaching mode was described involving expounding common difficulty, assigning and reading over the homework, individualized tutoring after school, on-line responding to the student's question, prompting the student to complete programming and answering questions in evening classes. It's pointed out that the individualized teaching has to take both common knowledge and student difference into considerations. Individulized mode enhances the teaching efficacy greatly.

Improvement in EIS diagnosis accuracy using a multi-frequency parameter analysis method: preliminary results.

In this work we assessed the validity of the multi-frequency parameter (MFP) analysis method in distinguishing EIS false positive results. We chose 15 subjects with invasive duct carcinoma as the control group in which EIS results were all positive. In the experiment, three test groups-the Contact, the Skin and the Horm groups-were set to correspond to three common types of EIS false results. In the Contact group, false positive results were induced by poor contact of the measuring probe. In the Skin group, false positive results were induced by skin ridges. In the Horm group, false positive results were induced by a high hormone level. Based on the MFP analysis method, we obtained the Cole-Cole parameters of each subject in the control group and the test groups. Statistical analyses showed there was a significant difference in G(0N), G(infinity)N) or alpha(N) between the control group and the Contact or the Skin group. A significant difference between the control group and the Horm group existed only in alpha(N). These results suggested that by means of the MFP analysis method it was possible to distinguish between a false positive result and a positive result caused by breast cancer. In conclusion, the MFP analysis method appears to be a feasible means to improve the diagnosis accuracy of EIS for breast cancer detection.

Image monitoring for an intraperitoneal bleeding model of pigs using electrical impedance tomography.

Current medical imaging techniques are not effective for timely detection of internal hemorrhage when the bleeding is slow and in small quantities. In this study, electrical impedance tomography (EIT) was applied to monitor the intraperitoneal bleeding of an animal model. Five healthy pigs three months old were used. The process of intraperitoneal bleeding was simulated with the injection of anticoagulated blood which was controlled by an electronic syringe pump. The injected rate was no more than 100 ml h(-1) and the total injection volumes ranged from 300 ml to 500 ml. Sixteen electrodes were attached to the abdomen and used for electrical current excitation and surface voltage measurement. Dynamic changes in impedance distribution within the abdomen were calculated by the back-projection algorithm and a series of EIT images were displayed in a unified range. The monitoring was performed with EIT at a rate of one frame per second and continued for at least 4 h. Intraperitoneal blood volume changes could be identified by inspection of consecutive EIT images during the progression of blood injection. 30 ml of blood in the peritoneum could be detected. EIT was shown to be a promising technique for continuous monitoring of intraperitoneal bleeding over periods of time.

An image monitoring system for intraperitoneal bleeding using electrical impedance tomography and its preliminary results in vivo.

An image monitoring system using electrical impedance tomography (EIT) for intraperitoneal bleeding was designed (FMMU V3.5). It consists of a constant current driving source with frequency of 50 KHz, a high accuracy measurement module, a driving and measuring mode program-controlled circuits, a data acquisition card, an optoelectronic isolated digital I/O board, and a custom-specified linear power supply units. The system applied equal-potential back projection algorithm to reconstruct dynamic images. The relative accuracy of the system is 0.1%, the RTI noise is 11.1 mu V (bandwidth 100 Hz). Based on physical phantom, images reconstructed by the system showed that it can image dynamically to the infused saline solution, and by infusing more solution the gray changed area of the image also enlarged accordingly. For stomach filling model in vivo, the dynamic imaging processes showed that the system can clearly and sensitively monitoring the saline solution drinking into the stomach for 50 ml each time, and by drinking more saline solution the conductivity changed area of the dynamic image also enlarged accordingly.

High precision Multifrequency Electrical Impedance Tomography System and Preliminary imaging results on saline tank.

To establish a high precision data acquisition system for multi-frequency electrical impedance tomography (EIT), a series of methods were introduced. Those methods include building a driving signal with up to four frequency components to diminish the effect of the dynamic change of tissues resistivity, extracting the impedance information by a digital demodulator that can improve the SNR by 8 times. The system that established can work at a wide range from 1.6kHz to 380kHz. Its CMRR is 74dB at 100kHz. The output impedance of current source is 2MΩ at that frequency. And measurement precision on a 100ohm resistor is better than -80dB in full bandwidth. Both the quasi-static and the dynamic imaging results based on a saline tank can reflect the resistivity changes inside the phantom clearly. Therefore, the system was competent in multifrequency EIT research work.

The influence of position to phase and magnitude detecting in medical magnetic induction imaging.

A 16-channel magnetic induction imaging system is introduced briefly. Highly precise phase and magnitude detecting method is applied to the information acquisition. The resolution of phase detecting is 0.003deg. The results of magnitude detecting also provide us with useful information. The characteristic curves are smoother than that of our previous system. One dimension results in different positions of the measurement region demonstrate the trend of variation of the detected signals. The positions of the object affect the results greatly and the trend of variation is regular.

Quasi-polar drive pattern for brain electrical impedance tomography.

To seek a single source drive pattern that is more suitable for brain electrical impedance tomography (EIT), a comparison between adjacent, cross, polar and newly proposed quasi-polar drive patterns was made in aspects of boundary voltages dynamic range, independent measurement number, Total boundary voltage changes and anti-noise performance based on an equivalent circuit of the brain resistivity distribution consisting of 7300-odd resistors. The results demonstrate that quasi-polar drive pattern is optimal in all the aspects except dynamic range. Polar and cross drive patterns come next, and adjacent drive pattern is the worst. Therefore, the quasi-polar drive pattern should be chosen for brain EIT.

Study of influencing factors on Electrical Impedance Scanning Imaging.

Electrical impedance scanning (EIS) is a new adjunctive diagnostic method for women breast cancer examination. In clinic research, we found some influencing factors which can induce a bad EIS imaging results. In order to analyze the influencing factors on EIS imaging and find the solutions, we set up an EIS workbench which can simulate the influencing factors that may happen in a clinic. We studied the influencing factors from size, depth of the target; the influence from the poor contact; the influence from the unparallel current field. The experiment results show that the detectability of EIS system is a function of the depth, the size and the area of electrodes; a good contact between the probe and the skin can decrease the artificial imaging; using the imaging algorithm can calibrate the imaging induced by unparallel current field.

A data acquisition system for induced current electrical impedance tomography / 生物医学工程学杂志

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.

A bipolar optocoupler isolation amplifier with high precision and wide bandwidth / 生物医学工程学杂志

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.

Frequency characteristic of diseased breast tissues detected by electrical impedance scanning / 生物医学工程学杂志

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.

A method of building the finite-element model with the contour line of human brain / 生物医学工程学杂志

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.

An experimental system of induced-current EIT / 生物医学工程学杂志

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.

Post-processing algorithm on images of electrical impedance tomography / 医疗卫生装备

Objective To study the image processing methods of electrical impedance tomography(EIT) in order to improve the display quality.Methods Evaluate the conductivity of the nodes using the conductivity of the adjacent triangle elements.The conductivity of any point in one triangle element was calculated according to the conductivity of 3 vertexes of the element by 2D linear interpolation method.Results The original blocky images of electrical impedance tomography by the triangle elements can be transformed into smoothing images.Conclusion The visual quality of the images is improved greatly.The image processing method is adaptive to all kinds of images of electrical impedance tomography based on triangle element.

The complex impedance frequency response and the equivalent circuit model of human brain / 生物医学工程学杂志

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.

In vivo measurement of rabbits brain impedance frequency response and the elementary imaging of EIT / 生物医学工程学杂志

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.

The impedance frequency response of the human skull / 生物医学工程学杂志

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.

Simulation study of the reconstruction algorithm for electrical impedance tomography based on the sensitivity theorem / 生物医学工程学杂志

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.