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

组织工程学的目标是通过将合适的支架和细胞结合在一起来开发“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，即捐赠者器官的短缺。虽然支架材料池很大(例如天然/合成生物材料)，但人们一致认为靶组织的细胞外基质(ECM)具有天然的结构和生物力学特性，是一个很好的选择。细胞外基质可以从身体组织(例如动物组织)通过一种称为脱细胞的过程获得，通过该过程，组织经历几个周期的洗涤剂和酶冲洗。一个成功的脱细胞组织的特征是没有细胞材料和存在完整的细胞外基质。用于评估细胞外基质的成像是开发温和而有效的脱细胞方法的极其重要的工具。该项目旨在开发一种新的成像工具，用于基于X射线微型计算机断层扫描(CT)来表征脱细胞组织。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测试其性能。相比之下，目前检查ECM的金标准技术(组织学、电子显微镜)要求对样本进行切片、切片和/或染色，为成像做准备，禁止在任何进一步研究中使用它们。在微型CT成为验证脱细胞技术和组织工程中其他方法的有价值的工具之前，还需要许多实质性的发展。目前，微型CT不能满足这一领域复杂的成像需求，这往往需要多尺度、多对比度的方法。首先，需要一台具有放大能力的微型CT机器来检查ECM的多层次结构。其次，脱细胞组织通常表现出微弱的X射线衰减；因此，Micro-CT机器应该提供相位对比和衰减对比，众所周知，这提供了比后者更好的组织支架可视化。这里提出的微型CT机将兼具这两种功能。它将利用一种创新的成像机制，这种机制的基础是通过放置在样品上游的掩膜将X射线束结构成一组窄的(微米)光束。这在空间分辨率方面提供了灵活性，因为这一度量--与传统的微型CT扫描仪不同--不是由源和探测器的模糊来定义的。取而代之的是，分辨率由光束宽度驱动，可以使其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，它提供了对互补对比通道(相位、超小角度X射线散射)的访问。这些通道是由于X射线与物质相互作用时伴随着衰减而产生的微小的X射线光子偏差造成的。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能够检测到这些影响，允许为每个样本重建三组互补的断层图像。虽然相位通道可以提供比衰减通道高得多的对比度噪声比，但超小角度X射线散射通道编码了样品中亚分辨率特征的存在。后者在图像引导放大方面具有独特的潜力。该项目将最终完成图像制导多尺度和多对比度成像实验原型的设计、建造和测试，其视场可达10厘米乘10厘米，未来可能会扩展到更大的维度。将对广泛的脱细胞组织进行扫描，结果将以当前的金标准(组织学或电子显微镜)为基准。

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).