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Electrical impedance tomography images of some of the key hardware system monitoring technology research

Author: MaJieShi
Tutor: DongXiuZhen；ShiXueTao
School: Fourth Military Medical University
Course: Biomedical Engineering
Keywords: Electrical impedance tomography Data Acquisition System Drivers and measurement USB data transfer DC power supply
CLC: TH772
Type: Master's thesis
Year: 2010
Downloads: 93
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Abstract

Electrical impedance tomography (Electrical Impedance Tomography, EIT) is a kind of the resistivity distribution within the body of the new imaging technique for imaging. It on biological tissue noninvasive, continuous, functional imaging, medical imaging is a very promising imaging technique. According EIT technical characteristics, Fourth Military Medical University research group presented the world's first electrical impedance image monitoring this new concept, and in 2006 developed the first set of EIT image monitoring system, expand the clinical image monitoring tests. In clinical trials, the system can change the body's resistance to effectively reflect, showing tantalizing prospect for clinical application. Clinical trials also study in-depth monitoring EIT hardware system for higher performance requirements, and thus some of the key technical requirements proposed improvements. EIT hardware system key technologies including power technology, excitation, signal detection technology, data acquisition technology, interface technology and drive - measurement and control technology. In order to make the EIT image monitoring system can better clinical application, it is necessary to research group existing EIT hardware system, based on some of its key issues: Drive - measurement control mode and data interface for further study in order to further improve the EIT Hardware system performance. In addition, in order to expand the EIT image monitoring system monitoring applications and reduce the volume and weight of the hardware system, this paper also three power supply EIT monitoring system performance of a comparative study, as follows: 1) Pre-grade drivers - Measurement Improved control mode to reduce the precision of the leads of the system, the hardware system program generation EIT excitation and measuring the electrical impedance of the front portion and separated from the host system, the nearest to the electrode system connected to conductor pattern to reduce as much as possible parameters on the measurement accuracy. Accordingly, the driving electrode and the measuring electrode also will forward selection control section. In this arrangement, the pre-stage and the system control line between the main control system than the existing line to be long, existing direct control methods are no longer applicable. To take into account the number and data communications data bus speed requirements, the maximum transfer speeds of up to 5Mbps high-speed serial peripheral interface (Serial Peripheral Interface, SPI) bus, based on improved data exchange protocol, the introduction of answering with a handshake signal, to achieve a new, more stable and reliable synchronous serial data interface bus, the front module can be a master device with the EIT for fast, interactive data exchange, thus ensuring the accuracy of data transmission. Based on the improved synchronous serial interface bus, this study adopts complex programmable logic device (Complex Programmable Logic Device, CPLD) as the front module control unit, and the use of ultra-high-speed integrated circuit hardware description language (Very high speed intergrated circuit Hardware Description Language, VHDL) on which the critical data transmission procedures for the preparation, realization of the control signal transmission, a new generation of EIT system pre-driver - measured control foundation. 2) suitable for EIT system USB data transmission module design in order to obtain more clinical application of a new generation of EIT imaging system must have a faster pace, requiring its data transfer interface with faster transfer speeds. Based on the interface, performance considerations, EIT image monitoring system chosen excellent performance of the USB interface. The interface in the EIT hardware system is mainly responsible for the hardware of the measured data upload and computer commands issued. The former involves the EIT image reconstruction, is the need to improve data transfer speed key. The current system in the measurement data upload USB chip only supports 8-bit data bus width, affecting the transmission speed. In order to expand a transfer of data, increase the transmission rate, this study used a 16-bit data bus width having a USB interface chip. USB interface in the current system control commands issued in batch transmission mode, there is a certain delay. In order to control commands transmitted with minimal delay EIT hardware system, interrupt transfer mode to complete the transfer. Based on the above considerations, the existing protocols based on USB1.1 USB interface, based on the design of a protocol based on USB2.0 data transmission module to complete the EIT system USB interface tasks. In this part of the work, based on the USB interface chip microcontroller with 16 dedicated DMA bus connection, the development of a USB data transmission module hardware board, the preparation of the microcontroller firmware, USB drivers, and test applications. Experimental results showed that: the module along with the control transfer, interrupt output transmission and batch input transfer function, can make the computer capable of USB data to initialize and read the USB device descriptor, making EIT software can be controlled with minimal delay EIT hardware system information to the measurement system and the system such that EIT measurement data can be quickly passed by DMA USB interface chip, and then passed to the computer. Maximum data transfer speeds of up to 675.2Kb / s, to meet two / second imaging speed data upload requirements. So as to establish a new generation of EIT system laid the foundation. 3) Power supply for the EIT system performance studies to meet the requirements of high-precision measurement of the current EIT image monitoring system used linear power supply. In order to make the EIT monitoring system for the field or in the future be able to transport equipment and other emergency situations without external power supply, this study considered the battery as the system power options; Meanwhile, in order to explore further reduce the EIT hardware system size and weight, further consideration the possibility of switching power supply. Therefore, for the above-mentioned three power performance of a comparative study: the use of spectrum analyzer were used to measure three kinds of DC power output spectrum and the corresponding excitation spectrum of the signal; DC power supply of the three conditions for data acquisition precision analysis; and three kinds of DC power supply conditions were EIT imaging results were compared. The results showed that: (1) battery power than linear power spurious, while the latter below the switching power supply; respectively in the three power supply, the excitation signal interference power is also above the size of the relationship with. (2), respectively, in the three power supply, the use of electrical impedance imaging system calibration data acquisition board test results showed that: a full-band excitation frequency battery power data acquisition accuracy than linear power supplies, and the latter is higher switching power supply; at low frequencies, three kinds of power supply under the data collection accuracy according to the above relationship, but little difference; at high frequency, battery-powered data acquisition accuracy slightly lower linear power supplies, which supply the data acquisition accuracy much higher switching power supply. Thus verifying the DC power supply for the EIT hardware system data acquisition accuracy influential. (3), respectively, of the three DC power supply, respectively, selection of 20kHz, 50kHz and 150kHz as low, medium, and high frequency excitation frequency, a scaling circuit board changes in resistance tests show EIT imaging battery power better image quality than linear power supply, which is better than the switching power supply. At low frequencies, the switching power supply when the image quality of power supply with the other two when the difference is minimal. According to the above test results, can be considered: the battery output spurious frequency points less, low power, can be used for EIT image monitoring system; while switching power supply, the excitation frequency of the low frequency band, EIT system performance and the other two power supply the case when the difference is small, which can use the excitation band for the EIT image monitoring system. Through the above three aspects of EIT hardware system key technologies, is expected to improve EIT image monitoring system performance, expand the image guardianship of the occasion, and to develop a new generation EIT system and lay a foundation for the EIT image monitoring to provide more effective technical support.

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