Gray J E, Trefler M
Med Phys. 1976 Jul-Aug;3(4):195-203. doi: 10.1118/1.594282.
The effect of phase on the quality of diagnostic radiological images is investigated on a theoretical basis and with the use of the computer simulations. Phase effects are divided into two categories: linear phase shift and asymmetric phase shift. Using a model of the x-ray focal spot distribution composed of two Gaussian functions, it is shown that the phase transfer function (PTF) is generally a continuous nonlinear function of spatial frequency. The linear phase shift serves only to shift the location of the image. The asymmetric phase shift in the model studied tends to accompany an improvement in the modulation transfer function (MTF) in the midfrequency region while introducing "wows" into the image. Contrast reversals are shown to be inherent in line spread functions (LSFs) which do not necessarily include linear or asymmetric phase effects, i.e., they are the result of another phenomenon.
在理论基础上并通过计算机模拟研究了相位对诊断放射图像质量的影响。相位效应分为两类：线性相移和非对称相移。使用由两个高斯函数组成的X射线焦点分布模型，结果表明相位传递函数（PTF）通常是空间频率的连续非线性函数。线性相移仅用于移动图像的位置。在所研究的模型中，非对称相移往往伴随着中频区域调制传递函数（MTF）的改善，同时在图像中引入“低频颤动”。对比度反转被证明在线扩散函数（LSF）中是固有的，这些线扩散函数不一定包括线性或非对称相位效应，即它们是另一种现象的结果。
