CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, FL 32816, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2019 Jan 10;64(2):025009. doi: 10.1088/1361-6560/aaf819.
X-ray diffraction tomography (XDT) resolves spatially-variant XRD profiles within macroscopic objects, and provides improved material contrast compared to the conventional transmission-based computed tomography (CT). However, due to the small diffraction cross-section, XDT suffers from long imaging acquisition time, which could take tens of hours for a full scan using a table-top x-ray tube. In medical and industrial imaging applications, oftentimes only the XRD measurement within a region-of-interest (ROI) is required, which, together with the demand to reduce imaging time and radiation dose to the sample, motivates the development of interior XDT systems that scan and reconstruct only an internal region within the sample. The interior problem does not have a unique solution, and a direct inversion on the truncated projection data often leads to large reconstruction errors in ROI. To reduce the truncation artifacts, conventional attenuation-based interior reconstruction problems rely on a known region or piecewise constant constraint within the ROI. Here we propose a quasi-interior XDT scheme that incorporates a small fraction of projection information from the exterior region to assist ROI reconstruction. In the phantom simulation, a small amount (17% of exterior region) of added exterior projection data improves the reconstruction quality by ~50%. The addition of exterior samplings in the experiment demonstrates improved spatial and XRD profile reconstructions compared to total-variation-based reconstruction or sinogram extrapolation. We expect our quasi-interior XDT to obviate the requirement on prior knowledge of the object or its support, and to allow the ROI reconstruction to be performed with the fast, widely-used filtered back-projection algorithm for easy integration into real-time XDT imaging modules.
X 射线衍射层析成像（XDT）可解析宏观物体中随空间变化的 XRD 分布，与传统基于透射的计算机层析成像（CT）相比，提供了更好的材料对比度。然而，由于衍射截面较小，XDT 的成像采集时间较长，使用台式 X 射线管进行全扫描可能需要数十个小时。在医学和工业成像应用中，通常只需要感兴趣区域（ROI）内的 XRD 测量，再加上减少成像时间和对样品的辐射剂量的需求，这就促使开发仅扫描和重建样品内部区域的内部 XDT 系统。内部问题没有唯一的解，直接对截断投影数据进行反演通常会导致 ROI 中的重建误差较大。为了减少截断伪影，传统的基于衰减的内部重建问题依赖于 ROI 内的已知区域或分段常数约束。在这里，我们提出了一种准内部 XDT 方案，该方案结合了来自外部区域的一小部分投影信息，以协助 ROI 重建。在体模模拟中，添加少量（外部区域的 17%）外部投影数据可将重建质量提高约 50%。实验中添加外部采样，与基于全变分的重建或射线图外推相比，提高了空间和 XRD 分布重建质量。我们期望我们的准内部 XDT 可以避免对物体或其支撑的先验知识的需求，并允许使用快速、广泛使用的滤波反投影算法进行 ROI 重建，以便轻松集成到实时 XDT 成像模块中。
