Baek Jongduk, Pelc Norbert J
Department of Radiology, Stanford University, Stanford, California 94305, USA.
Med Phys. 2009 Feb;36(2):394-401. doi: 10.1118/1.3050160.
An inverse-geometry computed tomography (IGCT) system uses a large source array opposite a smaller detector array. A previously described IGCT reconstruction algorithm uses gridding, but this gridding step produces blurring in the reconstructed image. In this article, the authors describe a two-dimensional (2D) IGCT reconstruction algorithm without gridding. In the transverse direction, the raw data of the IGCT system can be viewed as being composed of many fan beams. Because the spacing between source spots is larger than the spot width, each fan beam has undersampled projection data, but the missing samples are effectively provided by other undersampled fan beam views. In the proposed method, a direct fan beam reconstruction algorithm is used to process each undersampled fan beam. Initial images with this method showed ring artifacts caused by nonuniform sampling in the radial direction as compared to an ideal fan beam. A new method for correcting this effect was developed. With this correction, high quality images were obtained. The noise performance of the proposed 2D IGCT reconstruction algorithm was investigated, and it was comparable to that of the fan beam system. A MTF study showed that the proposed method achieves better resolution than the gridding method.
逆几何计算机断层扫描（IGCT）系统在较小的探测器阵列对面使用一个大的源阵列。先前描述的IGCT重建算法使用网格化，但这个网格化步骤会在重建图像中产生模糊。在本文中，作者描述了一种无网格化的二维（2D）IGCT重建算法。在横向方向上，IGCT系统的原始数据可视为由许多扇形束组成。由于源点之间的间距大于点的宽度，每个扇形束都有欠采样的投影数据，但缺失的样本可由其他欠采样的扇形束视图有效提供。在所提出的方法中，使用直接扇形束重建算法来处理每个欠采样的扇形束。用这种方法得到的初始图像显示，与理想扇形束相比，由于径向采样不均匀而产生环形伪影。开发了一种校正这种效应的新方法。通过这种校正，获得了高质量的图像。对所提出的二维IGCT重建算法的噪声性能进行了研究，其与扇形束系统的噪声性能相当。调制传递函数（MTF）研究表明，所提出的方法比网格化方法具有更好的分辨率。
