闪光层析成像散射修正计算研究

Study on Scattering Corrections in Flash Radiography

利用闪光照相成像系统底片信息,通过直接法对客体线性吸收系数空间分布进行重建,需能精确得到底片直穿量的信息,为解决这一问题必需对散射量进行修正。本文通过解析法推导出精确计算X光正向输运过程中未经碰撞与只经1次碰撞到达探测器处计数的理论公式,同时通过蒙特卡罗计算程序MCNP分析不同照相客体次级散射效应特性,对次级散射量进行数值修正,并由此编制快速光子正向计算程序SAT。与MCNP程序统计结果进行数值校验,结果表明,SAT程序能精确计算X光穿过照相客体到达探测器处的直穿量、散射量及总照射量计数,且计算速度远快于MCNP程序,这为闪光层析成像图像重建迭代扣除散射提供了快速精确的散射修正工具。

In order to reestablish the linear absorbing coefficients of the investigated object using the information of flash radiographic image, some image restoration procedures for a correction of the scattering effect are required. A theoretical model precisely calculating uncollided ray and the once-scattered ray flux of the detectors was established based on analytical method. The coefficients of the secondary scattered ray flux were also corrected by Monte-Carlo simulations of different investigated objects using the MCNP code. According to the above method an efficient analytic photon transport calculation code SAT was developed. Comparing the results of SAT code with that of MCNP code, it shows that the SAT code outperforms the MCNP code in terms of much less computing time with comparable precision. It provides a fast and precise procedure to correct the scattering effect based on iterative reconstruction of flash radiography.