粒状磷光增感屏点扩展函数的蒙特卡罗研究

磷光增感屏的内禀性质对磷光增感屏的成像性能影响很大.基于米氏(Mie)散射理论,计算得到磷光增感屏在不同颗粒尺寸和不同颗粒堆积密度情况下的散射系数和吸收系数.然后利用Monte Carlo(MC)方法模拟了可见光光子在磷光增感屏Gd₂O₂S:Tb(GOS)内的散射和吸收事件,得到磷光增感屏内不同位置处的可见光收集效率.利用MCNP程序模拟X射线束在磷光增感屏内的能量沉积分布,得到了金属-磷光增感屏总的点扩展函数(PSF).结果表明,在兆伏X射线成像系统中,使用小颗粒尺寸和高堆积密度的GOS磷光屏,可以改善增感屏系统的空间分辨率.

Monte Carlo Study on Point Spread Function of a Granular Phosphor Screen

Light absorption and scatteing coefficients of phosphor grain with different sizes and packing densities are computed with Mie theory.Optical photons in a granular phosphor screen are modeled by simulating scattering and absorption events of individual optical photons by Monte Carlo method (MC).Depth-dependent optical collection efficiencies are obtained.Using MCNP,distribution of energy deposition of 6 MeV mono-energetic X-ray in tungsten and phosphor screen is modeled.The point spread function of screen is given as a convolution of energy deposition kernel and optical kernel.Granular screens of smaller grain and higher packing density exhibit better spatial resolution in megavoltage radiography.