当对投影长度大于探测器长度的大型试件做平行光束CT时 ,可以认为投影被截断了。从数学上讲 ,这种情况下的解析法重建如滤波反投影法是不适宜的。然而从工程应用上来说 ,这又不是绝对的。就几种情况讨论了通过补充假数据 ,通过在 0～ 2π范围内对试件成像得到了完整的CT切片 ,获得了切片的精确重建 When parallel beam CT is performed on a large specimen with a projection length greater than the length of the detector, the projection can be considered as being truncated. Mathematically speaking, analytic reconstruction in this case, such as the filter backprojection is not appropriate. However, from the engineering application, this is not absolute. In several cases, the exact reconstruction of the slice was obtained by supplementing the fake data with a complete CT slice obtained by imaging the specimen in the range of 0 ~ 2π