Carlsson G A, Carlsson C A, Nielsen B, Persliden J
Phys Med Biol. 1986 Jul;31(7):737-49. doi: 10.1088/0031-9155/31/7/004.
Although field area and object thickness are important parameters in comparisons of techniques for optimal reduction of scattered radiation to the image, they are in practice seldom varied. For this reason, we suggest that contrast degradation (CDF) and contrast improvement (CIF) factors be more frequently used and appropriately defined to make the dependence of CDF and CIF on field area (collimation) and object thickness (compression) explicit. Definitions are formulated and the results of experiments and Monte Carlo calculations (comprising effects of collimation, compression, air gap, antiscatter grid, detector thickness) cited to illustrate their usefulness. Currently used expressions for CIF (derived assuming monoenergetic radiation) lack a factor to account for the change in primary contrast caused by the antiscatter method when this affects the energy distribution of the transmitted primary photons (grids and compression) or the fractions of photon energy imparted to the detector (when comparing different detectors). Values of this factor are calculated for some cases. Also, the appropriate choice of physical quantity to be used in the formulae for CDF and CIF is discussed. The energy imparted to the detector is advocated since this is directly related to the detector signals forming the image on, e.g. the x-ray film.
虽然在比较各种使散射辐射对图像的影响降至最低的技术时，照射野面积和物体厚度是重要参数，但实际上它们很少变化。因此，我们建议更频繁地使用并适当定义对比度降低因子（CDF）和对比度改善因子（CIF），以便明确CDF和CIF对照射野面积（准直）和物体厚度（压迫）的依赖性。本文给出了这些因子的定义，并引用了实验和蒙特卡罗计算结果（包括准直、压迫、空气间隙、反散射栅、探测器厚度的影响）来说明它们的用途。目前使用的CIF表达式（假设为单能辐射推导得出）缺少一个因子，该因子用于考虑当反散射方法影响透射原发射线光子的能量分布（栅和压迫）或赋予探测器的光子能量分数（比较不同探测器时）时，由反散射方法引起的原发射线对比度的变化。计算了某些情况下该因子的值。此外，还讨论了在CDF和CIF公式中应使用的物理量的适当选择。建议使用赋予探测器的能量，因为这与在例如X光胶片上形成图像的探测器信号直接相关。
