Kowalski G
Appl Opt. 1976 Mar 1;15(3):648-55. doi: 10.1364/AO.15.000648.
In radiography a pointlike x-ray source is used to generate the picture of an object. This simple shadow projection suffers from radiation being diffusely scattered by the object itself since it reduces considerably the contrast of the picture. To avoid this drawback it is proposed in this paper to introduce a grating between source and object of an incoherent shadow projection. The primary picture is modulated by this grating while scattered radiation is essentially not, thus being nearly invariant against a shifting of the grating. After electronic scanning the primary picture can be reconstructed by electronic demodulation. A projection of the grating with the object removed serves as the carrier frequency for the demodulation. In addition to the suppression of scattered radiation the application of gratings leads to enhanced spatial resolution. Taking multiple pictures with a shifted grating, the modulation transfer function is repeated several times within the frequency plane. A detailed mathematical treatment for a point source is given.
在射线照相术中，使用点状X射线源来生成物体的图像。这种简单的阴影投影存在一个问题，即辐射会被物体本身漫散射，这会显著降低图像的对比度。为了避免这一缺点，本文提出在非相干阴影投影的源和物体之间引入一个光栅。初级图像会被这个光栅调制，而散射辐射基本不会被调制，因此几乎不受光栅移动的影响。经过电子扫描后，初级图像可以通过电子解调来重建。去除物体后的光栅投影用作解调的载波频率。除了抑制散射辐射外，光栅的应用还能提高空间分辨率。使用移动光栅拍摄多张照片时，调制传递函数会在频率平面内重复多次。文中给出了点源的详细数学处理方法。
