Xu Jingzhu, Ham Kyungmin, Dey Joyoni
Louisiana State University, Department of Physics and Astronomy, Baton Rouge, Louisiana, United States.
Louisiana State University, Center for Advanced Microstructures and Devices, Baton Rouge, Louisiana, United States.
J Med Imaging (Bellingham). 2020 Mar;7(2):023503. doi: 10.1117/1.JMI.7.2.023503. Epub 2020 Mar 26.
We investigate an analyzer-less x-ray interferometer with a spatially modulated phase grating (MPG) that can deliver three modalities (attenuation image, phase image, and scatter images) in breast computed tomography (BCT). The system can provide three x-ray modalities while preserving the dose to the object and can achieve attenuation image sensitivity similar to that of a standard absorption-only BCT. The MPG system works with a source, a source-grating, a single phase grating, and a detector. No analyzer is necessary. Thus, there is an approximately 2x improvement in fluence at the detector for our system compared with the same source-detector distance Talbot-Lau x-ray interferometry (TLXI) because the TLXI has an analyzer after the object, which is not required for the MPG. We investigate the MPG BCT system in simulations and find a clinically feasible system geometry. First, the mechanism of MPG interferometry is conceptually shown via Sommerfeld-Rayleigh diffraction integral simulations. Next, we investigate source coherence requirements, fringe visibility, and phase sensitivity dependence on different system parameters and find clinically feasible system geometry. The phase sensitivity of MPG interferometry is proportional to object-detector distance and inversely proportional to a period of broad fringes at the detector, which is determined by the grating spatial modulation period. In our simulations, the MPG interferometry can achieve about 27% fringe visibility with clinically realistic BCT geometry of a total source-detector distance of 950 mm and source-object distance of 500 mm. We simulated a promising analyzer-less x-ray interferometer, with a spatially sinusoidal MPG. Our system is expected to deliver the attenuation, phase and scatter image in a single acquisition without dose or fluence detriment, compared with conventional BCT.
我们研究了一种无分析器的X射线干涉仪，它带有空间调制相位光栅（MPG），可在乳腺计算机断层扫描（BCT）中提供三种模态（衰减图像、相位图像和散射图像）。该系统能提供三种X射线模态，同时保持对物体的剂量不变，并且能实现与标准仅吸收式BCT相似的衰减图像灵敏度。MPG系统由一个源、一个源光栅、一个单相光栅和一个探测器组成。无需分析器。因此，与相同源 - 探测器距离的塔尔博特 - 劳X射线干涉测量法（TLXI）相比，我们的系统在探测器处的注量提高了约2倍，因为TLXI在物体之后有一个分析器，而MPG不需要。我们在模拟中研究了MPG BCT系统，并找到了一种临床可行的系统几何结构。首先，通过索末菲 - 瑞利衍射积分模拟从概念上展示了MPG干涉测量法的机制。接下来，我们研究了源相干性要求、条纹可见度以及相位灵敏度对不同系统参数的依赖性，并找到了临床可行的系统几何结构。MPG干涉测量法的相位灵敏度与物体 - 探测器距离成正比，与探测器处宽条纹的周期成反比，宽条纹周期由光栅空间调制周期决定。在我们的模拟中，对于总源 - 探测器距离为950毫米且源 - 物体距离为500毫米的临床实际BCT几何结构，MPG干涉测量法可实现约27%的条纹可见度。我们模拟了一种有前景的无分析器X射线干涉仪，它带有空间正弦MPG。与传统BCT相比，我们的系统预计能在单次采集时提供衰减、相位和散射图像，且不会增加剂量或注量。
