碘化汞材料固有空间分辨的蒙特卡罗模拟研究

采用蒙特卡罗方法模拟了直接转换X射线探测材料HgI2在医用X射线范围的固有空间分辨性能,模拟基于最新版本的EGSnrc模拟软件的用户代码DOSRZnrc,模拟了HgI2材料对无限小锥束入射X射线的调制传递函数(MTF)。考虑到荧光光子和散射光子重吸收,高速电子射程扩展以及离轴X射线入射对空间分辨力的影响,把模拟结果和文献解析方法获得的结果做了对比,两者符合较好。模拟结果表明,初级高速电子射程和入射角度对材料固有空间分辨力影响很大,材料分辨对入射X光子能量很敏感,高能时分辨力特性急剧变差,而对材料厚度很不敏感。相对于非晶硒(α-Se),HgI2材料具有更好的固有空间分辨力,尤其在50 keV能量以上时。在fMTF=0.5时,能量为20 keV,50 keV和100 keV的X射线入射,HgI2和非晶Se固有空间分辨力分别为390 lp/mm,170lp/mm,52 lp/mm和390 lp/mm,80 lp/mm,22 lp/mm。

Inherent Spatial Resolution of Mercuric Iodide by Monte Carlo Simulation

Mercuric iodide(HgI2),as a semiconductor detecting material directly absorbing X-ray,its inherent spatial resolution has been investigated for the medical diagnosis X-ray energy.The Monte-Carlo simulation is performed with an infinitesimal pencil-beam of X-ray incident on the HgI2 slab to determine its modulation transfer function(MTF).The simulation is based on the user code DOSRZnrc of the latest version of the EGSnrc,and these effects on HgI2 spatial resolution by the reabsorptions of fluorescence and scattered photons,expanded ranges of fast photoelectrons and off-axis incident angle,are considered and the simulated results accord with the literature analytic results well.The simulation results show that the ranges of primary fast photoelectrons and off-axis incident angle can affect the spatial resolution of the material greatly and the spatial resolution is sensitive to the incident X-ray energy since the modulation transfer function(MTF) decreases greatly with the increasing of X-ray energy,which however depends hardly on the thickness of the film.Compared with amorphous Se,HgI2 has a higher inherent spatial resolution,especially for above 50 keV X-ray energy.When fMTF=0.5,for X-ray photon energy of 20 keV,50 keV and 100 keV,the inherent spatial resolutions of HgI2 and amorphous Se are 390 lp/mm,170 lp/mm,52 lp/mm and 390 lp/mm,80 lp/mm,22 lp/mm,respectively.