应用于高能伽马射线源图像诊断的厚针孔设计

摘要

在伽马射线辐射源图像诊断中,一般使用厚针孔将辐射源产生的伽马射线图像成像在射线图像探测器上.由于射线具有较强的穿透效应,针孔具有较厚的厚度,厚针孔成像系统的空间分辨、能通量、有效视场等测试要求相互制约,必须给出最优的厚针孔结构设计.根据厚针孔成像系统的特点,模拟计算厚针孔成像系统的基本过程.计算结果表明,在最优厚针孔结构中,缩短直孔段长度,能够扩大成像系统的有效视场,其有效视场能够接近系统的极限视场,随直孔段长度的缩短,有效孔径相对增大,当直孔段长度约为一个自由程时,有效孔径增加约28%,但对系统的空间分辨影响较小,系统的空间分辨主要由孔径决定,提高成像系统的放大倍数能提高系统的空间分辨.最后,简要分析了厚针孔准直后冷心位置的各种变化.%Thick pinhole is used to project γ -ray image from the radioactive source to image detectors in γ-ray source radiographic diagnostics. The γ - ray has strong penetrating effect and the pinhole has certain thick.Thus the measuring requirements such as the spatial resolution, intensity, and effect field of view( FOV), must be restricted by one another. And the optimized design of the thick pinhole must be determined at the same time. Simulation and calculation of the thick pinhole imaging system based on its characteristics is performed.The results indicate that the effect field of view can be increased by shortening the straight hole length, and the effect aperture can be increased either ( the effect aperture would increase about 28％ while the straight hole length is about one free path) and it has little influence to the system spatial resolution. The system spatial resolution was determined mainly by the pinhole aperture and increasing the imaging system magnification factor.Moreover, the change of the cold heart position after thick pinhole collimating is analyzed .