Doubletask North York, Ontario, Canada.
J Xray Sci Technol. 2011;19(2):155-72. doi: 10.3233/XST-2011-0284.
In computer tomography (CT), truncated projections are produced due to scanning large objects with a detector that is limited in width. Applying filtered back-projection(FBP) method directly to truncated projections, the reconstructed image will contain truncation artifacts - bright rings on the boundary of region of interest (ROI). Extrapolation algorithms can be used to reduce the truncation artifacts; however extrapolations are usually double the length of the projection data; resulting in an increased calculation time. This paper introduces mixed extrapolation, which is a combination of exponential and quadratic extrapolation. It is proven that doubling the length of the projection data for the mixed extrapolation can be avoided. The projections were extrapolated according to the boundary values and their derivatives. The algorithm achieves equivalence to the extrapolation approach with negligible increased calculation time. Supplementary functions are introduced in order to simplify the calculations. These functions can be calculated prior to extrapolation process, hence the calculation time is significantly reduced. The calculation times are compared between fast extrapolation introduced in this paper and normal extrapolation with doubling the length of projection data.
在计算机断层扫描（CT）中，由于探测器的宽度有限，会对较大的物体进行扫描，从而产生截断的投影。直接将滤波反投影（FBP）方法应用于截断投影，重建图像将包含截断伪影 - ROI 边界上的亮环。可以使用外推算法来减少截断伪影；然而，外推通常是投影数据长度的两倍，从而导致计算时间增加。本文介绍了混合外推，它是指数和二次外推的组合。证明了可以避免为混合外推将投影数据的长度增加一倍。根据边界值及其导数对投影进行外推。该算法与可忽略计算时间增加的外推方法等效。引入了补充功能以简化计算。这些功能可以在进行外推之前进行计算，因此计算时间大大减少。比较了本文中引入的快速外推和将投影数据长度增加一倍的常规外推之间的计算时间。
