Sensor Optimization And System Design Of EIT Based On Ultrasonic Modulation

Electrical impedance is an inherent electrical property of organism,which contains rich information such as the pathological and physiological activities.The detection of biological electrical impedance information has an important significance in the diagnosis of disease and health assessment.Electrical impedance tomography(EIT)is a new generation of noninvasive imaging method after the morphology and structure imaging and is one of the important research subjects of the modern biomedical engineering medical imaging technology.However,the relatively low spatial resolution of the EIT restricts its practical application.Hybrid imaging techniques utilize couplings of physical modalities to image,which would improve the spatial resolution.As a new type of hybrid imaging method,ultrasound modulated EIT is expected to improve the spatial resolution of EIT by coupling the electric field and the acoustic field to increase effective information.The topic was mainly based on the background of ultrasound modulated electrical impedance tomography and aimed to improve the spatial resolution of EIT.Based on the optimization design of the sensor,the hardware platform for the detection of acousto-electric signals was set up.The main results and conclusions are as following:(1)The parameter optimization of electrical sensors was carried out aimed at ultrasound modulated EIT.The quality of the reconstructed image and the magnitude of the average acousto-electric signals were selected as the optimization indexes.The number and length of the electrodes as well as the location of electrodes and the slot size were considered.The laws of influence of structure parameters on the measurement and imaging results can be obtained by comparing the quality of the reconstructed image and the magnitude of the average acousto-electric signals.A group of optimized structure parameters of electrode array were summarized which can promote the application of ultrasound modulated EIT.(2)The detecting system of ultrasound modulated EIT was built which included the module of sinusoidal current source drive,the module of ultrasonic transmission circuit,the module of ultrasonic echo signal detection circuit,the module of acousto-electric signal detection circuit and the module of USB communication.(3)According to the requirements of function realization and logic design,the VHDL language was used to write the internal control procedures of FPGA.The exciting part includes sinusoidal current source and square wave ultrasonic excitation generated by FPGA-controlled DDS which motivates the ultrasonic transducer to emit ultrasonic.The ultrasonic must generate at the peaks and troughs of sinusoidal current source excitation to guarantee the relatively larger acousto-electric signal.Measurement part includes the gain amplification,AD digital sampling and USB data transfer controlled by FPGA.(4)The detecting system was debugged based on the completed hardware and the FPGA-controlled program.Then the corresponding experimental data was collected and analyzed.Finally,main research works and conclusions were summarized.