小型静态CT用多焦点X射线源电子束偏转系统研究

第5代全静态电子束CT（EBCT）能在被检测物体、射线源和探测器均处于静止状态下完成CT扫描成像。这种EBCT成像方式既可应用于粉体材料、生物活体样品等易形变物体的CT检测，又可应用于物流包裹、在役管线等的快速CT检测。高精度的电子束偏转系统是静态CT成像多焦点射线源的关键技术之一。本文基于麦克斯韦电磁场相互作用理论，探讨了电子束在均匀磁场、小偏转角、近轴区域内的散焦、畸变及灵敏度特性，研究了影响电子束扫描系统焦点位置重复精度的物理参数及电子束在靶平面上的扫描偏转量与偏转线圈电流的线性关系。并设计、加工制作了一种小型高精度多焦点X射线的电子束偏转扫描系统，实验采用直径0.1 mm标准针规电子束扫描DR投影图像序列，验证了电子束偏转系统有良好的偏转线性，偏转量正比于O点的磁场强度，而与电子束的位置等初始条件无关。实验通过电子束偏转系统控制电子束偏转扫描，获得了熔断式保险管（Ø100 μm）的250个 X 射线视角投影，完成了第5代全静态三维CT重建图像。

Research on Electron Beam Deflection System of Multi-focus X-ray Source for Small-size Stationary CT

The fifth-generation stationary electron beam computed tomography (EBCT) can obtain CT imaging in the static state of the detected object, X-ray source and detector. This EBCT imaging method can be applied to the CT detection of deformable objects such as powder materials and living biological samples, as well as the rapid CT detection of logistics packages and pipelines in service. High-precision electron beam deflection system is one of the key technologies for miniaturizing low-cost multi-focus X-ray source for a stationary CT system. Based on Maxwell’s theory of electromagnetic field interaction, the defocusing, distortion and sensitivity characteristics of electron beam in small deflection angle, paraxial region and mean magnetic field were studied theoretically. The physical parameters affecting the repetition accuracy of focal position of electron beam scanning system and the scanning deflection of electron beam on target plane were discussed, and the linear relationship between the transfer distance and the deflection coil current was also studied. A small high-precision electron beam deflection scanning system for multi-focus X-ray source system was designed and fabricated. The DR projection image sequences of a 0.1 mm diameter standard needle gauge were acquired by electron beam scanning method. Our experimental results show that the electron beam deflection system has good deflection linearity and the transfer distance is proportional to magnetic field intensity of origin, rather than the initial condition of the electron beam. The beam deflection system controls the electron beam deflection scanning, and 250 X-ray projections of a fused fuse (Ø100 μm) were obtained. The fifth-generation stationary three dimensional CT images were reconstructed.