Abstract: Helical cone-beam CT with half-cover scan can enlarge field-of-view of conventional helical cone-beam CT. Projections are transversely truncated at each view angle. Katsevich algorithm is an exact imaging algorithm, and can obtain good reconstruction image. This algorithm needs that data are not truncated on PI line. Therefore, conventional Katsevich algorithm is not directly used for half-cover scan. A non-PI line Katsevich algorithm is proposed according to the property of half-cover scan and analysis of conventional Katsevich algorithm. In the proposed algorithm, derivative of projection, not firstly rebinned in the Tam window, is directly filtered along row of planar detector. Backprojection interval is not PI interval, computed according to reconstruction point, but only 2π interval computed by z-coordinate. The result invalidates that the proposed algorithm avoids PI line and obtains complete image of inspected area.

Key words: Computed Tomography（CT） imaging, cone-beam helix, half-cover scan, PI line, Katsevich algorithm

摘要： 半覆盖螺旋锥束CT可以扩大传统螺旋锥束CT的视场区域，但是每个投影角下的投影数据都是横向截断的。Katsevich算法作为一种精确的重建算法，它可以得到质量较高的重建图像，但是它要求PI线上的数据是非截断的，无法直接应用于半覆盖的螺旋锥束CT。根据半覆盖螺旋锥束CT的特点和Katsevich算法本身的分析，提出了一种非PI线的Katsevich算法。它将求导后的投影数据直接沿探测器的行方向进行滤波，而不是将投影在Tam窗内重排后滤波。反投影时，也不需要根据重建点求相应的PI区间，而是直接根据重建点的z坐标求出的2π区间。实验结果表明，提出的成像方法避开了PI线对重建的影响，得到了待检测区域的完整图像。

关键词: CT成像, 锥束螺旋, 半覆盖扫描, PI线, Katsevich算法