MICROMEGAS探测器用于低剂量X射线成像的研究

Gaseous detector has been used for direct digital x-ray medical imaging, and proved that can be improved the imaging quality and decreased the patient's dose, thus help for health. MICROMEGAS, is one of good property novel gaseous detectors, has excellent position resolution (<100μm). It was employed as an X-ray imaging detector will improve the imaging quality, under the condition of keeping a low radiation dose. But a collection of most of the avalanche charge within the width of a single anode and loss of the position resolution, when anode wider than 400μm. The narrow anode will cost a lot of electronics. In order to solve this problem a thin polyethylene film and a thin film with high surface resistance is glued on the separate readout anode in turn. The resistive anode film forms a 2D RC network with respect to the anode. The charge arrived at the anode surface will be dispersed with RC time constant so as to fire the adjacent anode, that the center of gravity method can be utilized to improve the position resolution. Applied this technique to build one dimension position sensitive MICROMEGAS detector with 1mm anode strip pitches and reach 100μm accuracy approximately. We will be utilized with this detector to build a direct digital X-ray scanning imaging system and plan to obtain the imaging of the object which a width less than 10cm.

核辐射气体探测器应用于直接数字化X射线医学成像，在保证成像质量的基础上大大降低了患者接受的辐射剂量，对人们的健康有益。MICROMEGAS是一种高性能的新型气体探测器，具有优异的位置分辨（<100μm）能力。将它作为X射线成像的图像探测器能够在低辐射剂量条件下显著提高成像的质量。但是由于其阳极表面上感应电荷分布宽度小，在宽阳极上同一个触发事件不能引起相邻电极点火，导致重心法不能运用。针对这一问题，阳极上依次覆上聚酯薄膜和电阻性薄膜构成RC网络，阳极收集的电荷在RC网络中迅速传播增加了电荷的分布宽度，使得触发事件在较宽的阳极上引起点火的多重数增加，从而利用重心法提高探测器的位置分辨能力。将这一方法应用在一维位置灵敏的MICROMEGAS探测器上，实现在1mm宽度的阳极上位置分辨达到100μm。并将其作为图形探测器搭建一台直接数字化X射线扫描成像系统，对宽度小于10cm的物体实现扫描成像。

低剂量X射线数字化扫描成像对医学诊断和人体健康有着重要的意义。本项目利用Micromegas探测器通过逐事件记录入射的X射线，实现数字化扫描成像。在项目执行期间研制了一台灵敏面积10cm×15cm的Micromegas探测器。该探测器的阳极上敷贴了一层绝缘膜和1.5MΩ/□的电阻性介质，与阳极构成RC网络实现了电荷扩散读出。经测试在1mm周期的1维阳极上探测器的位置分辨达到46微米（σ）。搭建了一套由计算机控制步进电机，从而带动导丝杆移动的扫描位移平台，平台的位移精度好于20微米。探测器与扫描位移平台组合构成了扫描成像系统。对刻字的小样品实现了扫描成像。圆满的完成了项目内容。