一、引直自从十九世纪末伦琴发现x射线以来,x线成像技术已成为医学诊断的重要手段。可是,长期以来人们只能得到x射线透过物体所产生的二维投影图,这种投影图不能区分沿射线行进方向上物体层次的吸收差别,给诊断带来了困难。如果物体相对x线源及记录平面作相对运动,或者x线源连同记录平面对物体作相对运动,则在记录平面上得到不同投影条件下的投影图。能否从这些投影得到物体的三维吸收分布图,即完成所谓的图像重建,就成为长期以来力求解决的问题。实际上,三维吸收图可以由一系列的二维吸收断层迭合 I. Straightening Since the discovery of x-rays by Roentgen at the end of the nineteenth century, x-ray imaging has become an important tool in medical diagnosis. However, for a long time, people can only get two-dimensional projections of x-ray transmitted through objects, which can not distinguish the absorption differences of objects along the ray’s traveling direction, which brings difficulties to diagnosis. If the object relative to the x-ray source and the recording plane for relative motion, or x-ray source with the recording plane on the object for relative motion, the projection plane in the projection of different projection conditions. Obtaining the three-dimensional absorption profile of the object from these projections, that is, completing the so-called image reconstruction, has long been a problem that has to be solved. In fact, three-dimensional absorption maps can be superimposed by a series of two-dimensional absorption faults