应用刃边法测试计算机X线摄影系统预采样MTF

Measurement of the presampled MTF of computed radiography using an edge test device

目的:设计并应用高精度刃边装置测试计算机X线摄影系统(CR)的预采样MTF。方法:首先设计并制作一刃边装置;利用CR摄取一幅刃边像;对此数字图像处理得到预采样MTF,处理过程包括能量沉积计算,角度确定,重投影,平滑处理,ESF到MTF的转化等。结果:所测试的CR的预采样MTF分布:当空间频率为0.4lp/mm时,主、副扫描方向上的MTF分别为0.58、0.67;当空间频率为1.5lp/mm时,主、副扫描方向上的MTF分别为0.063,0.085;当空间频率为3.0lp/mm时,主、副扫描方向上的MTF分别为0.0011、0.0033。结论:刃边法是测试数字摄影系统预采样MTF简便易行的方法,可用于常规的质量控制和质量保证中。

Objective：To design a high-precision edge test device and to measure the presampled MTF of computed radiography system.Methods：An edge device had been designed and constructed from a m-thick lead foil laminated between two thin slabs of acrylic.The device was placed on the surface of IP,and the polished edge was parallel to the X-ray beam.A radiograph of the device was taken with an exposure,the image of the edge device was acquired and processed to obtain the presampled MTF.The image processing include calculation of the relative deposited-energy data,automated determination of the edge angle,reprojection,smoothing of the edge spread function（ESF）,and MTF synthesis from ESF.Results：The presampled MTF of CR in horizontal and vertical directions were 0.67 and 0.58 at 0.4 cycle/mm,0.085 and 0.063 at 1.5 lp/mm,0.0033 and 0.0011 at 3.0 lp/mm.Conclusion：The simplicity and practicality of edge test method allows routine and accurate determination of presampled MTF for digital radiographic systems.