Mechanical Engineering, University College London, UK; Diamond Light Source, UK.
Diamond Light Source, UK; National Synchrotron Light Source II, Brookhaven National Laboratory, USA.
J Mech Behav Biomed Mater. 2023 Feb;138:105579. doi: 10.1016/j.jmbbm.2022.105579. Epub 2022 Nov 19.
In-line phase contrast synchrotron tomography combined with in situ mechanical loading enables the characterisation of soft tissue micromechanics via digital volume correlation (DVC) within whole organs. Optimising scan time is important for reducing radiation dose from multiple scans and to limit sample movement during acquisition. Also, although contrasted edges provided by in-line phase contrast tomography of soft tissues are useful for DVC, the effect of phase contrast imaging on its accuracy has yet to be investigated. Due to limited time at synchrotron facilities, scan parameters are often decided during imaging and their effect on DVC accuracy is not fully understood. Here, we used previously published data of intervertebral disc phase contrast tomography to evaluate the influence of i) fibrous image texture, ii) number of projections, iii) tomographic reconstruction method, and iv) phase contrast propagation distance on DVC results. A greater understanding of how image texture influences optimal DVC tracking was obtained by visualising objective function mapping, enabling tracking inaccuracies to be identified. When reducing the number of projections, DVC was minimally affected by image high frequency noise but with a compromise in accuracy. Iterative reconstruction methods improved image signal-to-noise and consequently significantly lowered DVC displacement uncertainty. Propagation distance was shown to affect DVC accuracy. Consistent DVC results were achieved within a propagation distance range which provided contrast to the smallest scale features, where; too short a distance provided insufficient features to track, whereas too long led to edge effect inconsistencies, particularly at greater deformations. Although limited to a single sample type and image setup, this study provides general guidelines for future investigations when optimising image quality and scan times for in situ phase contrast x-ray tomography of fibrous connective tissues.
在线相位对比同步加速器断层扫描与原位力学加载相结合，通过数字体素相关（DVC）能够对整个器官内的软组织微力学进行特征化。优化扫描时间对于减少多次扫描的辐射剂量和限制采集过程中的样本运动很重要。此外，尽管软组织在线相位对比断层扫描提供的对比度边缘对 DVC 很有用，但相位对比成像对其准确性的影响尚未得到研究。由于同步加速器设施的时间有限，扫描参数通常在成像过程中确定，其对 DVC 准确性的影响尚未完全了解。在这里，我们使用先前发表的椎间盘相位对比断层扫描数据来评估以下因素对 DVC 结果的影响：i）纤维图像纹理，ii）投影数量，iii）断层重建方法，以及 iv）相位对比传播距离。通过可视化目标函数映射，获得了对图像纹理如何影响最佳 DVC 跟踪的更深入了解，从而能够识别跟踪不准确的情况。在减少投影数量时，DVC 受图像高频噪声的影响最小，但准确性会有所妥协。迭代重建方法提高了图像的信噪比，从而显著降低了 DVC 位移不确定性。传播距离被证明会影响 DVC 准确性。在提供最小尺度特征对比度的传播距离范围内，可获得一致的 DVC 结果；距离太短，提供的跟踪特征不足，而距离太长，会导致边缘效应不一致，尤其是在较大变形时。尽管本研究仅限于单一样本类型和图像设置，但它为未来优化纤维状结缔组织原位相位对比 X 射线断层扫描的图像质量和扫描时间的研究提供了一般指导。
