Three-dimensional quantitative x-ray phase imaging

X射线相衬成像是近年来X射线科学中出现的最令人兴奋的新方法之一。它基于折射和干涉现象而不是X射线衰减来生成图像对比度，从而增强图像中所有细节的可见性。此外，传统上被认为是“x射线不可见”的特征也可以被xpci探测到。这在许多应用中都具有变革性的力量，从医学到工业测试，通过生物学、文化遗产、材料科学、安全检查和许多其他领域。值得记住的是，x射线的使用在科学和社会中都是无处不在的，所有使用x射线成像的领域都可以从xpci中获得巨大的好处。直到几年前，xpci还被认为仅限于被称为同步加速器的大型、专业和昂贵的设施--世界上只有大约50个这样的设施。然而，我的研究小组最近解决了这个问题，开发了一种方法，使xpci能够在传统的x射线源上进行，就像医院使用的那样。这将使XPCI走出超专业的实验室，进入“真实世界”的应用，目前正在与多家公司进行谈判，以将该技术投入商业开发。该项目旨在开发下一代这项技术。目前，我们的XPCI方法仅适用于2D、“平面”成像应用程序。虽然这本身是有用的，并且在某些领域(例如，在机场进行乳房X光照相或行李扫描)是有效的，但许多其他应用程序需要对成像样本进行完整的3D(“断层”)重建。这在医学上是一个众所周知的问题，例如，一些疾病不能通过简单的“x光”诊断，但需要CT(计算机断层扫描)扫描；同样的原理也适用于许多其他领域，在这些领域，对样本的完整3D知识对于随后的决策过程至关重要。例如新药的开发，其效果通常是通过对其进行测试的小动物的高分辨率3D图像来评估的，或者在复杂的机械部件或新的“复合材料”的测试中。因此，该项目的目的是开发一种定量的、完整的3D版本的XPCI法。这需要克服一些障碍，其中一些障碍具有很强的技术性。例如，为了使x射线成像系统对x射线相位敏感，我们使用掩模，它覆盖了成像对象的部分。虽然这在平面成像中不会造成问题，但由于被覆盖的样本部分小于成像系统可以分辨的最小元素(探测器像素)，因此在重建3D体积时，由于被称为欠采样的问题，这确实会导致显著的伪影。这在其他学科(例如核医学)中也会遇到，研究人员已经开发出新的、更复杂的重建工具，可以解决或至少缓解这个问题。因此，我们计划使这些新的重建工具适应我们的XPCI方法的特定要求，以便能够执行可靠和定量的3D“阶段”重建。最初，这将基于广泛的模拟阶段，在此期间将在不同的数据集上测试不同的算法，这将使识别最有希望的算法成为可能。这之后将是一个实验阶段，我们将在真实的实验数据上测试算法：这将允许选择最佳解决方案并对其进行微调。最后，将有一个演示阶段，在此阶段，优化的3D方法将应用于实际的科学问题，例如关节软骨微小损伤的3D可视化(众所周知，传统X射线方法看不见)，或新一代复合材料中的侵入/缺陷的3D可视化。

X-Ray Phase Contrast Imaging (XPCI) is one of the most exciting new methods emerged in x-ray science over recent years. It generates image contrast based on refraction and interference phenomena rather than x-ray attenuation, which enhances the visibility of all details in an image. Moreover, features classically considered "x-ray invisible" can be detected by XPCI. This has transformative power in many applications, from medicine to industrial testing, through biology, cultural heritage, material science, security inspections, and many other fields. It is worth remembering that the use of x-rays is all pervasive, both in science and in society, and all areas where x-ray imaging is used can strongly benefit from XPCI.The problem up to a few years ago was that XPCI was considered restricted to large, specialized and expensive facilities called synchrotrons - only approximately 50 of which exist in the world. However, my research group has recently solved this problem by developing a method that enables XPCI to be performed with conventional x-ray sources, like those used in hospitals. This will allow taking XPCI out of ultra-specialized labs and into "real-world" applications, and negotiations with various companies are indeed underway to take the technology into commercial exploitation.This project aims at developing the next generation of this technology. At the moment, our XPCI method works only in 2D, "planar" imaging applications. Although this is useful in itself, and is effectively employed in some areas (e.g. mammography or baggage scanning at airports), many other applications require the full 3D ("tomographic") reconstruction of the imaged sample. This is a well known problem in medicine, where for example some diseases cannot be diagnosed with a simple "x-ray" but require a CT (computed tomography) scan; the same principle also applies to many other areas, where full 3D knowledge of the sample is essential to the decision-making process that follows. Examples are in the development of new drugs, the effect of which is often assessed through high-resolution 3D images of the small animals on which they are tested, or in the testing of sophisticated mechanical parts or of new "composite" materials.This project therefore aims at the development of a quantitative, full 3D version of our XPCI method. This requires overcoming a number of obstacles, some of which have a very technical nature. For example, in order to make x-ray imaging systems sensitive to x-ray phase, we use masks, which cover parts of the imaged object. Although this does not create a problem in planar imaging, because the portions of the sample which are covered are smaller than the smallest element the imaging system can resolve (the detector pixel), it does result in significant artifacts when a 3D volume is reconstructed, because of a problem known as undersampling. This is also encountered in other disciplines (for example nuclear medicine), and researchers have developed new, more sophisticated reconstruction tools which allow solving or at least mitigating this problem. We therefore plan to adapt these new reconstruction tools to the specific requirements of our XPCI method, so that reliable and quantitative 3D "phase" reconstruction can be performed.Initially, this will be based on an extensive simulation phase during which different algorithms will be tested on various datasets, which will enable identifying the most promising ones. This will be followed by an experimental phase in which we will test the algorithms on real experimental data: this will allow selecting the best solution and fine-tuning it. Finally, there will be a demonstration phase in which the optimized 3D method will be applied to real scientific problems, among which for example the 3D visualization of small damage in articular cartilage (notoriously invisible to conventional x-ray methods), or of intrusion/defects in new-generation composite materials.