Development And Study Of The Measurement System For Open Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) is an effective noninvasive imaging technique following the techniques of shape imaging and structure imaging, and is developed recently 30-years. Closed Electrical Impedance Tomography (CEIT) mainly centered on a circular 2-dimensional field, the electrode uniformly distributed in the measured object , around the electrode surrounded the entire cross-section as the imaging region, but encountered a CEIT, such as low resolution, the electrode position uncertainty calculate the market domain model and application of inconsistent field shape, skin contact impedance problem. Closed in order to overcome the electrical impedance tomography uncertain issues such as electrode location, open electrical impedance tomography (OEIT) using row electrode arrays, referenced from ultrasound scanning working mechanism, through row electrodes scanning the measured body, imaging goal is only the shallow area under the electrodes. By repeatedly moving row electrodes, get conductivity distribution for the whole measured body. Develop an effective solution to inconvenient placement of electrodes.The thesis based on Open Electric Impedance Imaging technology, carry out basic application research for OEIT , achieve to design a practicably, rapid, high resolution, high-precision measuring automatic instrument which provide high precise measurement data for image reconstruction software. After studying and analyzing the international design and methodology of Electrical Impedance Tomography instrument , developed CQU2 instrument for Open Electric Impedance Imaging. CQU2 using Direct Digital Synthesis (DDS) method to generate sinusoidal signal inject to the electrode, the sinusoidal current has a a range of 1-5mA, frequency at 10KHz-1MHz, the constant current source circuit used a negative capacitance compensation circuit and calibration network to improve the output impedance of current source. And also applicated Digital Phase-Sensitive Detection(DPSD) technology to obtain accurate amplitude and phase information between electrodes .The measurement Signal-to-Noise Ratioobtained up to 80dB , at the same time in order to obtain a fast measurement response time , design a high-speed data collector: up to 40MHz sampling rate of ADC(AD9228), using high speed FPGA (EP2C20F256C8) and Digital Dignal Processors(TMS320F2812), Voltage control variable gain amplifier used in the board to implement automatic measurement , and DSP processor control the gain for VGA under different measured objects . Experimental shows that range of the current source output impedance at 10KHz-1MHz is 6M-500KΩ.A large number of experiments show that CQU2 can work well with OEIT image software algorithms , and accurately locate eyewinker in the sink and agar model. Better distinguish low difference conductivity of the Organization. Also carry out a preliminary clinical experimentation for breast cancer patient , get valuable clinical data. It's be true that Open Electric Impedance technology will tend toward to clinical application in the future.