【作者】 蔡春鸣；

【导师】 彭承琳；

【作者基本信息】 重庆大学 ， 生物医学电子与信息技术， 2010， 硕士

【摘要】 随着医学与工程学的发展,基于功能性电刺激的人工视觉假体技术的研究及其成果为失明患者带来希望。人工视觉假体技术是将微电极阵列植入视觉通路中的某段神经处,电刺激器把视觉信息转换为电脉冲信号通过微电极阵列刺激相邻的神经节细胞,神经节细胞再将信息传入大脑,使患者感知到图像。各种视觉假体刺激的部位不同,但是基本功能是相同的,都需要将外界的光信号转换为可用的电流脉冲,通过微电极阵列刺激相关部位产生光幻视。电刺激器是视觉假体的关键部分,其功能是连接图像处理系统与刺激电极阵列,将图像信号转变为电流脉冲。本文设计了一款应用于视皮层假体的多通道电刺激器,实现将图像编码信号转换为电流脉冲的功能。采用FPGA作为主控芯片,在FPGA内部设计了刺激脉冲发生器,多路选择器和串并转换器。刺激脉冲发生器通过对FPGA的系统时钟计数,能够产生各种形式的脉冲信号,输入到多路选择器的信号输入端。在74164宏功能函数的基础上增加触发器级数实现了32位的串/并转换功能,通过读取图像处理系统传入的图像编码信号并将其转换为并行信号,同时控制16个多路选择器,从而实现16个通道的信号转换。为了将FPGA输出的电压信号转换为电流信号,设计了外围电压/电流转换电路,外围转换电路由多个压控双向恒流源单元电路构成。经测试,本文所设计的电压/电流转换电路具较好的转换线性和恒流特性。在EP1C6核心板的基础上制作了十六通道电刺激器初级样机,利用十六通道电刺激器初级样机与图像处理系统搭建了视皮层假体系统初级样机,并进行了图像测试。测试结果表明,系统初级样机可以将获取到的图像信息进行相应的处理并转化为相应的电流脉冲,对于变换的图像信息能够作出及时的反应,达到了预期的目标。本文采用多通道刺激器的样机进行了动物验证实验。采用猫作为实验对象,在猫的视皮层硬脑膜外左右两侧植入微电极,左侧接入刺激信号,右侧记录脑电,实验结果显示,视皮层能够响应来自对硬脑膜的电刺激,验证了本文所设计的刺激器是可行的。更多还原

【Abstract】 As the developing of medicine and engineering, artificial vision prosthesis based on functional electrical stimulation brings hopes to the blind. Artificial vision prosthesis technology implants a micro-electrode array in the visual pathway of certain nerve. An electrical stimulator is able to convert visual information into electronic pulses to stimulate the adjacent ganglion cells by micro-electrode array. Ganglion cells then pass the information the brain, so that patients can perceive the image. All visual prostheses have the same function: converting outside optical signal to certain current pulses and stimulating the relevant parts by the micro-electrode array to generated phosphenes. Electrical stimulator is to convert image information to current pulse in the vision prostheses.This paper designed a multi-channel electrical stimulator for the visual cortex prosthesis to convert image information to stimulation current. It uses FPGA as its main control chip. The FPGA comprises a spike generator, a serial-to-parallel converter and some multiplexers. The spike generator can generate various forms of pulse signal by counting the system clock, and put them into the signal input end of all multiplexers. The 32 bits serial-to-parallel converter is realized by increasing the trigger progression of macro function 74164. Serial-to-parallel converter can read the coded image signals and convert them to parallel signals to control 16 multiplexers simultaneously. Then the FPGA converts image signals to electrical pulse. In order to convert the output voltage signals to current signals, we designed peripheral conversion circuit. The peripheral conversion circuit contains some voltage-controlled bidirectional constant current source units. These voltage / current conversion circuits show good linearity and constant-current characteristics of conversion in testing. We made an initial prototype of 16-channel electrical stimulator based on the EP1C6 kernel board. And a system initial prototype of visual cortex prosthesis is made by the initial prototype of 16-channel electrical stimulator and an image process system. Result of testing shows that the system initial prototype can process image information correspondingly and convert image information to corresponding current pulse. And the prototype can make timely responses to the transformation of the image information. We performed the experimental evaluation by the initial prototype of 16-channel electrical stimulator. Put two electrode chips out of the left and right dura of cortex of a cat. Electrical stimulation was connected to the left one. Record the visual electrically evoked potential (EEP) by the right one. The results of experiment on cat’s cortex show that the cortex can respond to the current stimulation, and the initial prototype is feasible.更多还原