New York University School of Medicine, New York, NY, United States of America.
Phys Med Biol. 2019 Aug 7;64(15):155007. doi: 10.1088/1361-6560/ab2df1.
Low-dose x-ray CT is a major research area with high clinical impact. Compressed sensing using view-based sparse sampling and sparsity-promoting regularization has shown promise in simulations, but these methods can be difficult to implement on diagnostic clinical CT scanners since the x-ray beam cannot be switched on and off rapidly enough. An alternative to view-based sparse sampling is interrupted-beam sparse sampling. SparseCT is a recently-proposed interrupted-beam scheme that achieves sparse sampling by blocking a portion of the beam using a multislit collimator (MSC). The use of an MSC necessitates a number of modifications to the standard compressed sensing reconstruction pipeline. In particular, we find that SparseCT reconstruction is feasible within a model-based image reconstruction framework that incorporates data fidelity weighting to consider penumbra effects and source jittering to consider the effect of partial source obstruction. Here, we present these modifications and demonstrate their application in simulations and real-world prototype scans. In simulations compared to conventional low-dose acquisitions, SparseCT is able to achieve smaller normalized root-mean square differences and higher structural similarity measures on two reduction factors. In prototype experiments, we successfully apply our reconstruction modifications and maintain image resolution at quarter-dose reduction level. The SparseCT design requires only small hardware modifications to current diagnostic clinical scanners, opening up new possibilities for CT dose reduction.
低剂量 X 射线 CT 是一个具有高度临床影响的重要研究领域。基于视图的稀疏采样和稀疏正则化的压缩感知在模拟中显示出了前景，但这些方法在诊断临床 CT 扫描仪上实施起来可能很困难，因为 X 射线束无法快速开启和关闭。基于视图的稀疏采样的替代方法是间断射线稀疏采样。SparseCT 是一种最近提出的间断射线方案，通过使用多狭缝准直器 (MSC) 阻挡部分射线来实现稀疏采样。使用 MSC 需要对标准压缩感知重建管道进行许多修改。特别是，我们发现 SparseCT 重建在基于模型的图像重建框架内是可行的，该框架结合了数据保真度加权以考虑半影效应和源抖动以考虑部分源阻塞的影响。在这里，我们介绍了这些修改，并在模拟和真实原型扫描中展示了它们的应用。在模拟中，与传统的低剂量采集相比，SparseCT 能够在两个降低因子上实现更小的归一化均方根差和更高的结构相似性度量。在原型实验中，我们成功地应用了我们的重建修改，并在四分之一剂量降低水平上保持图像分辨率。SparseCT 的设计只需要对当前的诊断临床扫描仪进行微小的硬件修改，为 CT 剂量降低开辟了新的可能性。
