Prasad S C
Med Phys. 1979 May-Jun;6(3):229-32. doi: 10.1118/1.594570.
In computed tomography the finite width of the collimator aperture implies that the image is reconstructed from scans having finite strip width. This blurs the image and limits scanner resolution. Bracewell has discussed the nature of the blurring produced and suggested a method to partially restore the image under the assumption that the x-ray focal spot has a uniform intensity distribution. However, pinhole radiographs of x-ray focal spots reveal intensity distribution in the scanning plane which peaks at the edges of the focal spot with a reduced intensity in the center. A model is presented which simulates this intensity distribution as the sum of two point sources of x rays separated by a uniform line source. This results in a point absorber response function which is a superposition of two rectangular distributions and the one discussed by Bracewell. The corresponding tranfer function is derived which shows that the intensity distribution of the focal spot influences the high spatial frequency components of the reconstructed image more than the low frequency components.
在计算机断层扫描中，准直器孔径的有限宽度意味着图像是由具有有限条带宽度的扫描重建而成的。这会使图像模糊并限制扫描仪的分辨率。布雷克韦尔讨论了所产生模糊的性质，并提出了一种在假设X射线焦点具有均匀强度分布的情况下部分恢复图像的方法。然而，X射线焦点的针孔射线照片显示，扫描平面中的强度分布在焦点边缘处达到峰值，而中心处强度降低。本文提出了一个模型，该模型将这种强度分布模拟为两个由均匀线源分隔的X射线点源之和。这导致了一个点吸收器响应函数，它是两个矩形分布与布雷克韦尔所讨论的分布的叠加。推导了相应的传递函数，结果表明焦点的强度分布对重建图像高频分量的影响大于对低频分量的影响。
