Chakraborty D P, Barnes G T
Med Phys. 1983 Jul-Aug;10(4):467-9. doi: 10.1118/1.595310.
The methodology employed to calculate radiographic signal-to-noise ratio (SNR) for the commonly used disk-shaped test object is reviewed. Although the "matched" aperture yields the maximum SNR, its shape is difficult to achieve experimentally. On the other hand, a circular aperture having the same size as the object is much simpler to realize. We have performed a numerical analysis of the SNRs obtained with matched and circular apertures for two screen/film systems (a mammographic and a general purpose combination) for a range of test-object sizes. We find that for object sizes greater than 0.5 mm in diameter, there is a less than 4% difference between the SNRs obtained with the two apertures. The shapes of some of the matched apertures are also presented. We conclude that the SNR determined with the circular aperture is a simpler and more useful determinant of system performance for the screen/film combinations studied.
回顾了用于计算常用圆盘形测试物体的射线照相信噪比（SNR）的方法。尽管“匹配”孔径能产生最大的信噪比，但其形状在实验中很难实现。另一方面，与物体尺寸相同的圆形孔径则更容易实现。我们针对一系列测试物体尺寸，对两种屏/片系统（乳腺摄影系统和通用组合系统）使用匹配孔径和圆形孔径所获得的信噪比进行了数值分析。我们发现，对于直径大于0.5毫米的物体尺寸，两种孔径所获得的信噪比之间的差异小于4%。文中还给出了一些匹配孔径的形状。我们得出结论，对于所研究的屏/片组合，用圆形孔径确定的信噪比是一种更简单且更有用的系统性能决定因素。
