Bracewell R N
J Comput Assist Tomogr. 1977 Jan;1(1):6-15. doi: 10.1097/00004728-197701000-00003.
X-ray measurements made by scanning in a plane, in successive position angles, involve a degradation (smoothing, or blurring) associated with the nonzero width of the strip occupied by the X-ray beam. The collimating holes that define the X-ray beam cannot be made indefinitely small without increasing the X-ray source power indefinitely. However, making a tomogram from the strip integrals is usually handled as though the data consisted of line integrals. The result is that each infinitesimal element of the tomogram is spread out into a density distribution resembling a cone with a central crater. Restoration of the tomogram to correct for the blurring associated with the strip width is warranted and will receive greater attention as the precision of measurements increases and as demand for resolution approaching that of conventional radiography begins to push instrumental design against various limits. Restoration is a well-developed subject, but in each field of application has its own peculiarities. Systematic and statistical properties of tomograms, the character of their errors, and the desired information will influence the future development of restoration in tomography. X-ray tomography is also special in that diffraction of the rays is negligible and that sharp shadow edges may be formed.
通过在平面内以连续的位置角度进行扫描来进行X射线测量，会涉及到与X射线束所占据的条带的非零宽度相关的退化（平滑或模糊）。在不无限增加X射线源功率的情况下，限定X射线束的准直孔不能被制作得无限小。然而，从条带积分制作断层图像通常被当作数据由线积分组成来处理。结果是，断层图像的每个无穷小元素被扩展成一个类似于带有中心坑的圆锥体的密度分布。对断层图像进行恢复以校正与条带宽度相关的模糊是有必要的，并且随着测量精度的提高以及对接近传统放射成像分辨率的需求开始推动仪器设计达到各种极限，这将受到更多关注。恢复是一个发展成熟的主题，但在每个应用领域都有其自身的特点。断层图像的系统和统计特性、其误差的特征以及所需的信息将影响断层成像中恢复技术的未来发展。X射线断层成像也很特殊，因为射线的衍射可以忽略不计，并且可以形成清晰的阴影边缘。
