A new multi-scale x-ray micro computed tomography machine to enable (image-guided) non-destructive inspections of decellularised tissue

组织工程——旨在通过结合合适的支架和细胞来开发“实验室培养”的器官和组织——可以解决我们这个时代最大的医学问题之一，即供体器官的短缺。虽然支架材料池很大（例如天然/合成生物材料），但人们一致认为目标组织的细胞外基质（ECM）是一个很好的选择，因为它具有天然的结构和生物力学特性。体外干细胞可以通过一种叫做脱细胞的过程从尸体组织（例如动物）中获得，通过这种过程，组织要经历几次洗涤剂和酶的冲洗循环。成功脱细胞组织的特征是细胞物质的缺失和完整ECM的存在。用于评估ECM的成像是开发温和有效的脱细胞方法的极其重要的工具。这个项目是关于开发一种新的成像工具，用于表征基于x射线微计算机断层扫描（CT）的脱细胞组织。由于micro-CT是一种非破坏性技术，被检查的样品可以进一步用于纵向研究或植入动物体内以测试其在体内的表现。相比之下，目前检查ecm的金标准技术（组织学，电子显微镜）要求样品被切片，切片和/或染色以准备成像，禁止在任何进一步的研究中使用它们。在micro-CT成为验证组织工程中脱细胞技术和其他方法的有价值的工具之前，还需要大量的实质性发展。目前，微型ct无法满足该领域复杂的成像需求，往往需要多尺度、多对比度的方法。首先，需要一台具有放大功能的微型ct机来检查ecm的多层次结构。其次，脱细胞组织一般表现为微弱的x射线衰减；因此，微型ct机器应该提供相位对比和衰减对比的访问，已知衰减对比比后者提供更好的组织支架可视化。这里提出的微型ct机将具有这两种功能。它将开发一种创新的成像机制，该机制的基础是通过放置在样品上游的掩模将x射线束结构成一组狭窄的（微米级）光束。这在空间分辨率方面提供了灵活性，因为这个度量-与传统的微型ct扫描仪不同-不是由源和检测器的模糊定义的。相反，分辨率是由光束宽度驱动的，可以使光束宽度小于固有的系统模糊，具有快速分辨率切换和多尺度成像的独特潜力。其次，它提供了互补对比通道（相位，超小角x射线散射）的访问。这些通道是由x射线与物质相互作用时伴随衰减而发生的x射线光子小偏差造成的。虽然大多数传统的微型ct扫描仪对这些影响视而不见，但这里提出的机器将使其检测成为可能，允许为每个样品重建三组互补的层析成像图像。虽然相位通道可以提供比衰减通道高得多的对比噪声比，但超小角x射线散射通道编码了样品中存在的亚分辨率特征。后者具有图像引导放大的独特潜力。该项目最终将设计、建造和测试一个用于图像引导的多尺度和多对比度成像的实验原型，其视场可达10cm × 10cm，未来可能会扩展到更大的尺寸。将扫描范围广泛的脱细胞组织，并根据当前的金标准（组织学或电子显微镜）对结果进行基准测试。

Tissue engineering - aimed at developing "lab-grown" organs and tissue by combining appropriate scaffolds and cells - could solve one of the biggest medical problems of our times, the shortage of donor organs. While the pool of scaffold materials is large (e.g. natural/synthetic biomaterials), there is consensus that the extracellular matrix (ECM) of the target tissue is an excellent choice as it possesses native structural and biomechanical properties. ECMs can be derived from cadaver tissue (e.g. from animals) through a process called decellularization, by which the tissue undergoes several cycles of flushing with detergents and enzymes. A successfully decellularised tissue is characterised by the absence of cellular material and the presence of an intact ECM. Imaging, for assessing the ECM, is an extremely important tool for the development of decellularisation methods that are simultaneously gentle and effective.This project is about developing a new imaging tool for characterising decellularised tissue based on x-ray micro computed tomography (CT). Since micro-CT is a non-destructive technique, the inspected samples can be used further in longitudinal studies or be implanted into animals to test their performance in vivo. In comparison, the current gold standard techniques for inspecting ECMs (histology, electron microscopy) require that samples are sliced, sectioned and/or stained in preparation for being imaged, prohibiting using them in any further studies. A number of substantial developments will be needed before micro-CT can become a valuable tool for validating decellularisation techniques and other methodologies in tissue engineering. Currently, micro-CT fails to meet the complex imaging needs of this field, which often requires multi-scale and multi-contrast approaches. First, a micro-CT machine with zooming in capabilities would be required to inspect the multi-level structure of ECMs. Second, decellularised tissue generally exhibits weak x-ray attenuation; hence, the micro-CT machine should provide access to phase contrast alongside attenuation contrast, which is known to provide a much better visualisation of tissue scaffolds than the latter. The micro-CT machine proposed here will have both these functionalities. It will exploit an innovative imaging mechanism that is underpinned by the idea to structure the x-ray beam into an array of narrow (micrometric) beamlets via a mask placed immediately upstream of the sample. This provides flexibility in terms of spatial resolution, as this metric - unlike in conventional micro-CT scanners - is not defined by the blur of the source and detector. Instead, resolution is driven by the beamlet width, which can be made smaller than the intrinsic system blur, bearing unique potential for fast resolution switching and multi-scale imaging. Second, it provides access to complementary contrast channels (phase, ultra-small angle x-ray scattering). These channels result from small x-ray photon deviations which occur alongside attenuation when x-rays interact with matter. While most conventional micro-CT scanners are blind to these effects, the machine proposed here will enable their detection, allowing to reconstruct three sets of complementary tomographic images for each sample. While the phase channel can provide a much higher contrast-to-noise ratio than the attenuation channel, the ultra-small angle x-ray scattering channel encodes the presence of sub-resolution features in a sample. The latter bears unique potential for image-guided zooming in. The project will culminate in the design, construction and test of an experimental prototype for image-guided multi-scale and multi-contrast imaging with a field of view of up to 10 cm by 10 cm, which may be expanded to larger dimensions in the future. A broad range of decellularised tissues will be scanned, and the results benchmarked against the current gold standard (histology or electron microscopy).