Tilley Steven, Siewerdsen Jeffrey H, Stayman J Webster
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, USA.
Phys Med Biol. 2016 Jan 7;61(1):296-319. doi: 10.1088/0031-9155/61/1/296. Epub 2015 Dec 9.
While model-based reconstruction methods have been successfully applied to flat-panel cone-beam CT (FP-CBCT) systems, typical implementations ignore both spatial correlations in the projection data as well as system blurs due to the detector and focal spot in the x-ray source. In this work, we develop a forward model for flat-panel-based systems that includes blur and noise correlation associated with finite focal spot size and an indirect detector (e.g. scintillator). This forward model is used to develop a staged reconstruction framework where projection data are deconvolved and log-transformed, followed by a generalized least-squares reconstruction that utilizes a non-diagonal statistical weighting to account for the correlation that arises from the acquisition and data processing chain. We investigate the performance of this novel reconstruction approach in both simulated data and in CBCT test-bench data. In comparison to traditional filtered backprojection and model-based methods that ignore noise correlation, the proposed approach yields a superior noise-resolution tradeoff. For example, for a system with 0.34 mm FWHM scintillator blur and 0.70 FWHM focal spot blur, using the correlated noise model instead of an uncorrelated noise model increased resolution by 42% (with variance matched at 6.9 × 10(-8) mm(-2)). While this advantage holds across a wide range of systems with differing blur characteristics, the improvements are greatest for systems where source blur is larger than detector blur.
虽然基于模型的重建方法已成功应用于平板锥束CT（FP-CBCT）系统，但典型的实现方式既忽略了投影数据中的空间相关性，也忽略了由于探测器和X射线源中的焦点造成的系统模糊。在这项工作中，我们为基于平板的系统开发了一个正向模型，该模型包括与有限焦点尺寸和间接探测器（例如闪烁体）相关的模糊和噪声相关性。这个正向模型用于开发一个分阶段的重建框架，其中投影数据先进行去卷积和对数变换，然后是广义最小二乘重建，该重建利用非对角统计加权来考虑采集和数据处理链中产生的相关性。我们在模拟数据和CBCT测试台数据中研究了这种新型重建方法的性能。与忽略噪声相关性的传统滤波反投影和基于模型的方法相比，所提出的方法在噪声分辨率权衡方面表现更优。例如，对于一个具有0.34毫米半高宽闪烁体模糊和0.70半高宽焦点模糊的系统，使用相关噪声模型而不是不相关噪声模型可将分辨率提高42%（方差匹配为6.9×10(-8)毫米(-2)）。虽然这种优势在具有不同模糊特性的广泛系统中都成立，但对于源模糊大于探测器模糊的系统，改进最为显著。
