Phase modulation technology for X-ray imaging

我们计划开发基于相干的X射线成像方法，这种方法具有解决广泛物理问题的巨大潜力，并有望看到广泛的用途，特别是在钻石的I13光束线上。相干是同步加速器设施能力的一个相对较新的补充，并不是所有的应用都被探索过。正如我们计划的那样，通过从现有的可见光能力中转移技术，我们可以学到很多东西。用于X射线的格栅需要高纵横比和小(50纳米)特征尺寸，可以在Harwell现场制造。基于光栅的测量技术正处于发展的早期阶段，并将在这一提议下发展，以造福于材料和生物成像界。微制造在现代X射线成像中一直扮演着重要的角色。自1952年阿尔伯特·贝兹提出使用菲涅尔波带片制造X射线显微镜以来，X射线成像仪一直受益于微细加工工业的快速发展。X射线波带片是目前X射线显微镜的关键技术。通过电子束写入制造它们的现代实践是由麻省理工学院和IBM团队在80年代初率先提出的，现在可以提供外区宽度(大致等于分辨率)为10至15 nm的软X射线波带板。其他类型的微加工对象，如分辨率测试图案、Zernike相环、均匀冗余阵列，以及列表继续增长。戴蒙德的I-13光束线是一家世界级的设备，可以提供推进技术所需的高度相干光束。它的两个分支对应于两种基本的成像模式，即实空间和相互空间，这将提供基线能力：i)用于具有幅度或相位对比度的3D体积成像的X射线计算机层析成像(CT)。使用计算将一系列旋转的投影视图组装成3D图像。Ii)相干衍射成像(CDI)，通过对晶体样品的正向或布拉格峰周围的衍射图进行相移和随后的反转来实现。然而，CDI确实需要一个计算阶段步骤，为此，现在已经有了好的算法，更好的算法正在积极开发中。在更长的时间尺度上，所提出的方法开发将与钻石光束线B-24对接，用于低温传输X射线显微镜(TXM)。该项目需要尽可能高质量的菲涅尔波带板在水窗口中运行，这可以通过哈威尔微制造设施的精心规划的升级路径来实现。由于X射线成像计划完全依赖于这些项目的制造者，因此英国研究人员应该能够常规访问制造设施，最好是在英国境内，最好是在STFC内，这一点至关重要。在这个项目中有专门的全职人员从事X射线光学工作将是朝着这个方向迈出的第一步。通过我们将开发的新方法实现的研究将在可视化生物、医学和材料科学涉及的过程细节方面得到广泛应用。我们将开发的方法的灵活性还将使我们能够对类似过程进行动态研究，以及对需要复杂操作、包装和/或极端压力/温度条件的样品进行成像。我们的项目范围非常广，从只能通过衍射(CDI)才能获得的纳米级结构到大规模的整体动物研究，必然需要很大的视野。目前，所有这些X射线成像方式都在快速增长。该项目的重点是通过相位调制实现的增强，要么通过改善图像对比度，要么通过首先允许它们成像(分阶段地)来扩大可获得的样本的范围。

We plan to develop coherence-based X-ray imaging methods, which have great potential for solving a wide range of physical problems and are expected to see wide usership, especially at Diamond's I13 beamline. Coherence is a relatively new addition to the capabilities of synchrotron facilities and not all of its applications have been explored. There is much to learn by transferring technology from existing visible-light capabilities, as we plan. Gratings for X-rays, which need high aspect ratio and small (50-nanometer) feature sizes, can be manufactured on site at Harwell. Grating-based measurement techniques are in the early stages of development and will be developed under this proposal for the benefit of the materials and biological imaging communities.Microfabrication has always played an important role in modern x-ray imaging. From the 1952 proposal by Albert Baez to use Fresnel zone plates to build an x-ray microscope, x-ray imagers have profited from the rapid advances in the microfabrication industry. X-ray zone plates are now the key technology for x-ray microscopes. The modern practice of making them by electron-beam writing was pioneered by the MIT and IBM groups in the early eighties and can now deliver soft X-ray zone plates with an outer zone width (which roughly equals the resolution) of 10 to 15 nm. Other types of microfabricated objects, such as resolution test patterns, Zernike phase rings, uniformly redundant arrays, and the list continues to grow. Diamond's I-13 beamline is a world-class facility which can provide the highly coherent beams needed to advance the technology. Its two branches correspond to the two basic modes of imaging, in real and reciprocal space, which will provide the baseline capabilities:i) X-ray computed tomography (CT) for 3D volume imaging with amplitude or phase contrast. A rotational series of projection views is assembled into a 3D image using computation. ii) Coherent Diffraction Imaging (CDI) by phasing and subsequent inversion of diffraction patterns, either in the forward direction or around Bragg peaks from a crystalline sample. CDI, however, does require a computational phasing step, for which good algorithms are available now and better ones are under active development.On a longer time scale, the proposed methods development will interface with Diamond beamline B-24, for cryogenic Transmission X-ray Microscopy (TXM). This project needs the highest possible quality Fresnel Zone Plates operating in the water window , which could be achieved with a well-planned upgrade pathway for the Harwell microfabrication facility. Since x-ray imaging programs are totally dependent on the fabricators of these items, it is vital that routine access to the fabrication facilities should be available to UK researchers, preferably within the UK, and preferably within STFC. Having a dedicated full-time person in place working on X-ray optics within this project will be a first step in this direction.The research enabled by the new methods we will develop will see wide application in visualising the details of processes involved in biological, medical and materials science. The flexibility of the methods we will develop will also enable undertaking dynamical studies of similar processes, as well as the imaging of samples requiring sophisticated manipulation, housing and/or extreme pressure/temperature conditions. Our project has very broad scope, ranging from nanoscale structures accessible only though diffraction (CDI) to macroscale whole animal studies, necessarily requiring a large field of view. All these X-ray imaging modalities are seeing rapid growth at the present time. This project focuses on enhancements achievable by phase modulation, either by improving image contrast or by broadening the range of accessible samples by allowing them to imaged (phased) in the first place.