基于插值数浮动的MTF精确测量方法

采用刀口法测量成像系统调制传递函数(MTF)时,刀口装置与探测器矩阵夹角的准确测量是难点和关键点之一.针对这一问题,首先模拟刀口图像倾角对应的理论基准插值,研究了加载噪声情况下插值数浮动与线扩散函数(LSF)波动性变化以及MTF曲线衰减特性的定量关系;接着对实际X射线数字化成像系统获得的特定倾角下的刀口边缘图像进行了基于插值浮动的MTF测量,并将由其获得的MTF值与线对卡结果进行比较,证明了该方法用于成像系统MTF测量的有效性.结果表明:角度测量误差造成实际插值数偏离理想基准插值,导致LSF曲线光滑性变差,MTF衰减程度高于实际衰减.通过插值浮动方法,能够有效地避免角度测量误差引起的MTF测量的误差,降低角度测量的高精密性要求.

Accurate Measurement of MTF Based on Interpolation Floating Method

When employing the edge method to measure the modulation transfer function （MTF） of the imaging system, accurate measurement of the angle between the edge device and the detector matrix is one of the difficulties and key points. Regarding this problem, and according to theoretical benchmark in- terpolation of the edge angle of analog image, we firstly investigated the quantitative relationship between the interpolation floating and the changes in volatility of the line spread function （LSF） as well as the at- tenuation characteristics of the MTF curves in the presence of noise. Further, based on the interpolation floating method, we measured the MTF curves of the edge images under particular angle acquired by the actual X-ray digital imaging system. And great consistency was achieved between the MTF of the test card and that obtained with the method proposed, which verifies the effectiveness of the method for MTF meas- urement in the imaging system. The results show that the angle measurement error causes actual interpo- lation number deviation from the ideal benchmark interpolation which leads to worse smoothness of the LSF curves and higher attenuation level of the MTF curves than actual attenuation. With the interpolation floating method, the MTF measurement error because of the edge angle measurement error can be effec- tively avoided, and the high precision angle measurement requirements can he significantly reduced.