Johns P C, Yaffe M
Med Phys. 1982 Mar-Apr;9(2):231-9. doi: 10.1118/1.595076.
Scatter-to-primary energy fluence ratios (S/P) have been studied for fan x-ray beams as used in CT scanners and slit projection radiography systems. The dependence of S/P on phantom diameter, distance from phantom to image receptor, and kilovoltage is presented. An empirical equation is given that predicts S/P over a wide range of fan beam imaging configurations. For CT body scans on a 4th-generation machine, S/P is approximately 5%. Scattered radiation can produce a significant cupping artefact in CT images which is similar to that due to beam hardening. When multiple slices are used in scanned slit radiography, they can be arranged such that the increase in S/P is negligible. Calculations of scatter-to-primary ratios for first order scattering showed that for fan beams the contribution of coherent scatter is comparable to or greater than that of incoherent first scatter.
已经对CT扫描仪和狭缝投影射线照相系统中使用的扇形X射线束的散射与原发射线能量注量比（S/P）进行了研究。给出了S/P对体模直径、体模到图像接收器的距离以及千伏的依赖性。给出了一个经验方程，该方程可预测在广泛的扇形束成像配置范围内的S/P。对于在第四代机器上进行的CT体部扫描，S/P约为5%。散射辐射可在CT图像中产生明显的杯状伪影，这与由于束硬化产生的伪影类似。当在扫描狭缝射线照相中使用多层时，可以将它们排列成使得S/P的增加可以忽略不计。一阶散射的散射与原发射线比的计算表明，对于扇形束，相干散射的贡献与非相干一次散射的贡献相当或更大。
