闪烁体衰减常数对辐射源边界测量影响数值模拟

Numerical simulation of scintillant decay constant effect on radiation source boundary measurment

在辐射成像系统测量辐射源边界中,有闪烁体时间弥散效应得到的边界值与没有闪烁体时的真实边界值存在差别,影响辐射源尺寸变化计算。研究构建了一类辐射源强时间宽度、半径扩散速率与边界相对强度不同的辐射源,应用卷积和图像强度梯度法,对选用BC408,LaBr3和LSO闪烁体得到的边界与真实边界的偏差进行了数值模拟计算。结果表明,拍摄时间为20ns时,由BC408闪烁体得到的边界值偏差最小;若偏差小于1mm认为闪烁体适合测量,BC408,LaBr3和LSO测量的强度时间宽度最小值分别为33ns,133ns和266ns;拍摄全积分图像时偏差大小不受闪烁体不同的影响;最终得出的偏差计算公式较好地反映了真实偏差的变化趋势。

In the measurement of radiation source boundary using radiation imaging system, time diffusion of scintillant affects the measurement result. We constructed a type of radiation source having different intensity time width, boundary diffusion speed and relative intensity, then computed the deviation betweens boundary real size with the sizes in cases of scintillants BC408, LaBr3 and LSO respectively, by means of convolution and image intensity gradient. The results show that while photography time is 20 ns, deviation will be the smallest with the scintillant BC408; since a scintillator is not suitable for the measurement when deviation is greater than 1ram, the minimum values of intensity time width should be 266 ns, 133 ns and 33 ns for scintillants LSO, LaBr3 and BC408, respectively; however, the deviation doesn＇t vary with scintillant materials in complete integral imaging. Finally, a formula is summed up for deviation computation, which can well reflect the trend of real deviation.