尺寸测量是工业CT的一个重要应用方向，但工业CT检测是非直接测量方式，尺寸测量是通过CT像素尺寸和像素值作为特征量来计算并实现的。当尺寸接近或小于有效射束宽度（BW）的小细节或小缺陷尺寸测量时，使用常规的半高宽方法的测量误差很大，测量方法不再适用。采用调制传递函数曲线为特征量，通过软件统计计算等效直径的方法来确定小缺陷的尺寸。经过试验验证，这种测量方法对小缺陷尺寸的测量精度最差为13.8%，87%以上的测量结果精度优于10%，具有有效性和适用性。

Dimension measurement is one of very important application fields of ICT detection. Compared with general method, ICT uses the pixel size and value to get the real value. But if the size of item is closed to the BW (effective beam width), half width method will cause large error and is no longer applicable. In order to solve this problem, at this paper, the MTF curve was chosen as the characteristic quantity and mathematics software was used to calculate the size of the small defects. In our experiments, through using this method we get the result that the measurement error is 13. 8% at most, whereas the error for more than 87% of measurements is less than 10%. So we can get the conclusion that this method is effective.