BACKGROUND:The electrical impedance tomography (EIT) is a kind of examination that is used to non-invasively measure the change and distribution of electrical bio-impedance by reconstructing the frequency response obtained by electrical stimuli applied onto the human body. The characteristics of impedance of any tissues are of great importance to the imaging of EIT and locating and monitoring the lesion focus.OBJECTIVE: To measure the human brain impedance in the frequency range from 0.1 Hz to 1 MHz and to compare these with those of other human tissues and the rabbit brain tissues.DESIGN: An observational experiment.SETTING:The Department of Medical Electric Engineering of the Biomedical Engineering College of the Fourth Military Medical University of Chinese PLA.MATERIALS:The experiment was conducted at the Otolaryngology Laboratory, Department of Medical Electric Engineering of Biomedical Engineering College, Fourth Military Medical University of Chinese PLA from April, 2000 to June, 2000. Two brains were harvested from two cadavers of adult men who died in less than 12 hours before the brains were taken.INTERVENTIONS :The brains were divided into 15 samples and the Solartron 1255B frequency resoonse analyzer was used to measure the complex impedance of human brain in vitro with four-electrode measurement method in the frequency range from 0.1 Hz to 1 MHz.There were also impedance interface (1294)and self-made experimental measurement box.MAIN OUTCOME MEASURES:The resistivity frequency response,curves of real part and imaginary part of complex impedance as well as the equivalent circuit model of the complex impedance.RESULTS:The resistivity of human brain tissues was about 1 200 Ω·cm in the frequency range of 0.1-100 Hz.But it decreased to 650 Ω·cm in the frequency range of 100-1×106 Hz. The real part of complex impedance remained steady in the frequency range of 0.1-100 Hz and it decreased along with the increase of frequency in the range of 100-1×106 Hz. The absolute value of frequency response curves of the imaginary part of human brain's complex impedance presented a tendency of monotonic increase.CONCLUSION: The resistivity and the real part of complex impedance curve of human brain were in accordance with those of other tissues such as muscles, the liver, kidney and lungs. The frequency response curve of the imaginary part of human brain's complex impedance was different from that of other animal tissues (such as muscles, the liver and kidney) but was in accordance with that of rabbit brain tissues in vitro. The construction of the equivalent circuit model obtained was more complex than other models known.

BACKGROUND: Electrical impedance tomography (EIT) uses non-invasive signals to probe the human body and then detect the responses on the boundary of the body in order to reconstruct an impedance distribution inside the body. Compared to CT and MRI, EIT takes the advantages of realtime technique, lower cost and easiness for both continuous monitoring and functional imaging.OBJECTIVE: This study was designed to perform the in vivo measurement of the rabbit brain impedance frequency response before and after ischemia. And it was to verify the feasibility of EIT in brain functional imaging by ischemia brain functional imaging using EIT.DESIGN: It was a single-sample experiment.SETTING: It was conducted at the Department of Medical Electronic Engineering, Faculty of Biomedical Engineering, Fourth Military Medical University of Chinese PLA.MATERIALS: This study was conducted at the Department of Medical Electronic Engineering, Faculty of Biomedical Engineering, Fourth Military Medical University of Chinese PLA from August to September 2001 and 10 healthy rabbits were selected.METHODS: Cerebral ischemia animal model was made using carotid artery ligation. Then the in vivo measurement of the rabbit brain impedance frequency response before and after ischemia was performed.Dynamic unilateral brain blood supply was recorded using EIT imaging.curves were plot before and after ischemia in the frequency range from 0.1 Hz EIT imagingRESULTS: Nine rabbits entered the statistical analysis and one was omitimpedance increased significantly. The ratio of increasing impedance can be up to 75% at frequencies lower than 10 Hz. And in the range from 1 kHz namic imaging showed that the changes in unilateral brain blood supply is accordant with the corresponding regions having a changing impedance.CONCLUSION: The changes in brain tissue impedance before and after ischemia can be imaged and it could be used as a variable for EIT imaging.

In recent years,the research of non-contact biomedical monitoring has continuous development and progress.This review gives an overview of the research status of heart,lung and brain non-contact monitoring methods.The correlation techniques of capacitance electrocardiogram,magnetic induction,radar non-contact monitoring of heart and lung,and non-contact monitoring of brain are analyzed comprehensively.Capacitance electrocardiogram monitors the heart and lung activities useing effect of change in capacitance between the electrodes.Magnetic induction monitors the heart and lung activities useing the Maxwell principle,while radar monitoring the heart and lung activities uses the Doppler effects.Non-contact monitoring of brain adopts the magnetic induction tomography imaging technology.Then elaborate related research at home and abroad,and summarize the advantages and disadvantages of these monitoring methods on the basis of the analysis of monitoring principles.Finally foreground that may dominate this area of new equipment for heart,lung and brain non-contact monitoring in the future is expected.

In the magnetic induction tomography(MIT) system,the electrical conductivity of biological tissue is direct proportion to the phase difference between the excitation signal and the detection signal.To obtain the image of the contribution of tissue's electrical conductivity,the system must have the function of phase detection with high accuracy.The paper focuses on the means of digital phase detection,including FFT method,the correlation method and the classic method,which are ultimately compared with analogue phase detection method.The experimental results show that FFT method and the correlation method,with low error level and high linearity,can better detect the phase difference with the level of 0.1?.The digital phase difference detection provides a kind of effective method for MIT system.

In recent years,with the increasement of intracranial pressure detection accuracy,the use of intracranial pressure detection in clinic become more common.Various of technologies are used in clinic that can be divided into invasive methods,such as epidural catheter,subarachnoid bolt,intraventricular catheter,fiberoptic catheter and micro-sensors transducer,and non-invasive methods,such as evoked otoacoustic emissions,transocular method,transcranial doppler,imaging method and magnetic induction method.This paper reviews the physiological basis of intracranial pressure detection and common intracranial pressure detection techniques,especially on noninvasive intracranial pressure detection methods.Advantages and disadvantages of different intracranial pressure detection methods are listed,and an outlook of the development of non-invasive intracranial pressure detection technology are made.

The real-time monitoring of cerebral hemorrhage can reduce its disability and fatality rates greatly. On the basis of magnetic induction phase shift, we in this study used filter and amplifier hardware module, NI-PXI data-acquisition system and LabVIEW software to set up an experiment system. We used Band-pass sample method and correlation phase demodulation algorithm in the system. In order to test and evaluate the performance of the system, we carried out saline simulation experiments of brain hemorrhage. We also carried out rabbit cerebral hemorrhage experiments. The results of both saline simulation and animal experiments suggested that our monitoring system had a high phase detection precision, and it needed only about 0.030 4s to finish a single phase shift measurement, and the change of phase shift was directly proportional to the volume of saline or blood. The experimental results were consistent with theory. As a result, this system has the ability of real-time monitoring the progression of cerebral hemorrhage precisely, with many distinguished features, such as low cost, high phase detection precision, high sensitivity of response so that it has showed a good application prospect.
Algorithms ; Animals ; Cerebral Hemorrhage ; diagnosis ; Computer Systems ; Magnetics ; Rabbits ; Software

This study was aimed to improve the sensitivity of magnetic induction phase shift detection system for cerebral hemorrhage. In the study, a cerebral hemorrhage model with 13 rabbits was established by injection of autologous blood and the cerebral hemorrhage was detected by utilizing magnetic induction phase shift spectroscopy (MIPSS) detection method under the feature band. Sixty five groups of phase shift spectroscopy data were obtained. According to the characteristics of cerebral hemorrhage phase shift spectroscopy under the feature hand, an effective method, B-F distribution, to diagnose the severity of cerebral hemorrhage was designed. The results showed that using MIPSS detection method under feature band, the phase shift obviously growed with increase of injection volume of autologous blood, and the phase shift induced by a 3-mL injection reached -7.750 3 degrees ± 1.420 4 degrees. B-F distribution could effectively diagnose the severity of cerebral hemorrhage. It can be concluded that the sensitivity of the cerebral hemorrhage magnetic induction detection system is improved by one order of magnitude with the MIPSS detection method under the feature band.
Animals ; Cerebral Hemorrhage ; diagnosis ; Magnetic Phenomena ; Magnetics ; Rabbits ; Spectrum Analysis ; methods

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 ; Computer Simulation ; Electric Impedance ; Tomography ; methods

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 ; Amplifiers, Electronic ; Electric Impedance ; Electrodes ; Electromagnetic Fields ; Electromagnetic Phenomena ; instrumentation ; Humans ; Image Processing, Computer-Assisted ; Phantoms, Imaging ; Tomography ; instrumentation ; methods

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 ; Brain ; physiology ; Electric Impedance ; Electrodes ; Humans ; In Vitro Techniques ; Male ; Models, Biological