锥束螺旋CT半覆盖扫描的重建算法

目的：锥束螺旋CT能够解决长物体的检测问题，但是它的视场直径受限于面板探测器的宽度。为扩大锥束螺旋CT的视场直径，本文研究了一种视场区域半覆盖扫描的螺旋CT扫描方法和相应的重建方法。方法：扫描时，转台沿垂直于中心射线的方向水平平移一定距离，然后用普通螺旋CT的扫描方式即可获得需要的投影。重建时，利用推广的偏心锥束螺旋FDK（Feldkamp-Davis-Kress）算法，推广后的重建算法与标准的螺旋FDK算法具有同样的计算效率，而且不需要重排投影数据。结果：实验结果表明，本文提出的扫描方法能够将螺旋锥束CT的视场半径扩大0.86倍；重建图像的质量与使用大探测器全覆盖的标准FDK算法基本相当；由于投影数据量的减少，使重建时间比使用大探测器的标准FDK减少了376.66秒。结论：锥束螺旋CT的半覆盖扫描可以有效扩大视场直径，且具有较高的计算效率和较少的重建时间。

Half-cover Offset FDK Algorithm of Helical Cone-beam CT

Objective: The cone-beam helical computed tomography (CT) can scan the long object, but conventional x-ray CT imaging is based on the assumption that the entire cross-section of an object is illuminated with x-rays at each view angle. When inspecting large object, the conventional scanning mode is limited due to the width of planar detector. As an alternative, this paper developed field of view (FOV) half-cover scan such that slightly more than one half of required projection data is acquired. Method: When scanning, the gantry is translated horizontally, which direction is vertical to center ray. Then the conventional helical scan is executed. During reconstruction, the extended FDK (Feldkamp-Davis-Kress) algorithm is proposed with no rebinnging needed, and it is computationally as efficient as conventional helical cone-beam FDK algorithm. Result: Experimental results indicate that the FOV half-cover scan can extend the field of view up to 1.86 times, and the image quality, which is reconstructed by improved algorithm with small planar detector, is almost similar to the conventional algorithm with large planar detector. The reconstruction time is reduced 376.66 seconds due to the decrease of projections. Conclusion: The half-cover scan of helical cone-beam CT can extend the diameter of the field of view, and extended FDK algorithm is efficient.