【作者】 赵丽英；

【导师】 李刚；

【作者基本信息】 天津大学 ， 生物医学工程， 2010， 硕士

【摘要】 日常生活或临床手术中,金属异物可能进入或滞留体内,对人体产生一定的危害,多数情况下必需取出。体内金属异物的准确定位是其快速取出的首要条件,现有的定位方法中金属探测仪是一种简单便携又无损害的定位方式。此外,金属探测仪可以检测隐藏的金属物体,广泛应用于国防、公安、海关的安全检查以及建筑施工中。但是目前大多数金属探测仪的抗干扰能力差,测量灵敏度较低,不能对探测目标定位。针对这些问题,本文利用各种微弱信号检测方法,探索和设计了一种基于涡流传感原理的具有高灵敏度、高稳定度、实现方法简单方便的体内金属物无创探查系统,也可作为金属探测仪使用。金属探测仪是基于金属导体的涡流效应,应用涡流传感器非接触测量位移的方法来实现的。初步的涡流传感实验说明小金属物的涡流效应很微弱,系统实现的关键是对微弱变化信号的高灵敏度、高分辨率检测,因此,将数字锁相检测技术、过采样技术和系统比例测量方法相结合,根据系统的设计要求制定了实现方案并在此基础上搭建了体内金属物的无创探查系统。设计的体内金属物无创探查系统从激励源、传感器本身、测量电路和信号采集处理多方面进行研究和改良,从而提高检测灵敏度和可靠性。该系统通过控制单元实现信号激励和采集处理同步进行,提高了系统的稳定性;采用自制的检测线圈,并将恒流源电路和谐振电路相结合,简化了测量电路,提高了检测的灵敏度;采用数字锁相检测技术对变化微弱的交流信号进行处理,以滤除待测频率以外的各种噪声,提高信噪比;运用过采样技术进一步提高了ADC的转换精度,降低了系统的本底噪声,提高了检测精度和分辨率;引入系统比例测量方法,减小了激励信号幅值波动及ADC基准电压波动对系统测量精度的影响。由于体内小金属物的涡流效应很微弱,对于测量电路和信号采集处理方法有较高的要求。根据数字锁相检测算法的不同要求,分别搭建了以ADuC841和ADSP-BF506F为控制单元的系统,并对不同金属物进行了位置检测实验。通过对系统灵敏度、稳定性和精度的评估可知,对20mm×15mm×0.8mm的铁块、铜块及一元硬币,在0～60mm范围内,系统能准确探查出金属物的有无,并能检测到金属物的位置,空间分辨率小于5mm,同时系统对不同性质的金属物有一定的定性分辨能力。与现有的金属探测仪相比,该系统简单易用,抗干扰能力强,重复性好,为体内金属异物的快速排查定位提供了一种简便实用手段。更多还原

【Abstract】 In daily life or clinical surgery, metallic foreign body may enter or remain in vivo, causing a lot of harm to human bodies, and most of time it must be removed. The exact location of metallic foreign bodies is the primary condition for fast removing. Among the existing positioning methods, metal detector is a simple, portable and non-invasive way. In addition, the metal detector can detect hidden metal objects, which is widely used not only in safety inspection in national defense, public security, customs, but also in building construction. But most of the metal detectors at present have poor anti-interference ability, low measurement sensitivity, and can not locate the target. To solve these problems, we use a variety of weak signal detection methods to explore and design a non-invasive detection system of metal objects in vivo with high sensitivity, high stability, simple to implement and convenient to employment, which is based on eddy current sensing method. It can also be used as a metal detector instrument.Metal detector is based on the eddy current effect of metal conductor; use the non-contact displacement measurement methods of eddy current sensor to achieve. Preliminary experiments of the eddy current sensor show that the eddy current effect of the little metal objects are very weak, and the key of the system is how to achieve high-resolution and high-sensitivity detection of weak change signal. Therefore, the system was designed combining the digital lock-in detection, over-sampling techniques with systemic scaling method. And the implementation plan was developed according to the design requirements for the system. On this basis, non-invasive detection system of metal in vivo was designed.The non-invasive detection system of metal objects in vivo was improved from many aspects, including the excitation source, the sensor itself, the measurement circuit and the signal acquisition and processing method, to improve the sensitivity and reliability of detection. The system synchronized the excitation with the acquisition and processing of the signal by the control unit to improve the stability; using home-made detection coil and combining constant current source circuit with the resonant circuit to simplify the measurement circuit, and to improve the sensitivity of detection; using digital lock-in detection technique in the processing of weak changes of AC signal to filter out a variety of noise other than the tested frequency, to improve signal to noise ratio; furthermore, using over-sampling technique to improve the conversion accuracy of ADC, reduce the ontology noise of the system and improve the detection accuracy and resolution; using systemic scaling measurement method to reduce the influence on measurement accuracy caused by the fluctuations of the excitation signal amplitude and the ADC reference voltage.As the eddy effect of the metal in vivo was very weak, there were higher requirements for the measurement circuit and signal acquisition and processing methods. According to the different requirements of digital lock-in detection algorithm, systems using ADuC841 and ADSP-BF506F as the control units were built, then the detection experiments on different metal objects were carried out. The assessment of sensitivity, stability, and accuracy of the system show that the detection system had an accuracy of nearly 5mm in the range of 0 ~ 60mm for the iron block, the copper block of 20mm×15mm×0.8mm, and a dollar coin. Compared with the existing metal detectors, this system is simple to use,has a good anti-jamming ability and reproducibility, and provides a convenient and practical means for fast detection and location for metallic foreign bodies in vivo.更多还原