In micro-tomography, variants of helical X-ray source trajectories, e.g., double-helix (DH) and space-filling (SF), are attractive alternatives to the conventional circular trajectory, as they satisfy data-sufficiency conditions; this enables exact reconstruction, and large cone-angle (or high flux) imaging. Geometric alignment of micro-tomography experimental data, i.e., radiographs or projection data, to the required micron precision is a difficult problem. In this paper, we consider criteria based on differences in attenuation along opposing rays as a postacquisition software alignment technique. These opposing rays are called PI-lines and lie on lines that intersect two points of the scanning trajectory and pass through the region of support. The PI-line difference method is particularly appealing due to its low computational cost and small set of inherent assumptions, however, previous studies have exposed some limitations in precision. The number and distribution of PI-lines is highly dependent on the trajectory and thus so is the robustness of PI-line difference; here we show that DH and SF trajectories are particularly amenable to this technique. For these trajectories, we observe that the technique is applicable to both static and per-projection alignment estimation. We present results where PI-line difference alignment estimates are of equivalent accuracy as alignment estimates obtained from existing state-of-the-art methods: a tomogram sharpness method for static alignment and a reprojection-alignment method for per-projection alignment. In both cases, the computational expense of PI-line difference alignment estimation is a fraction of the tomogram-based methods.

中文翻译：

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用于锥束螺旋轨迹显微断层扫描数据对齐和运动校正的PI-line差异

在显微断层扫描中，螺旋形 X 射线源轨迹的变体，例如双螺旋 (DH) 和空间填充 (SF)，是传统圆形轨迹的有吸引力的替代方案，因为它们满足数据充足条件；这可以实现精确重建和大锥角（或高通量）成像。将显微断层摄影实验数据（即射线照片或投影数据）几何对准到所需的微米精度是一个难题。在本文中，我们将基于沿相反光线衰减差异的标准视为一种采集后软件对齐技术。这些相反的光线称为 PI 线，位于与扫描轨迹的两个点相交并穿过支撑区域的线上。PI 线差分法由于其低计算成本和少量固有假设而特别有吸引力，但是，先前的研究暴露了一些精度限制。PI 线的数量和分布高度依赖于轨迹，因此 PI 线差异的稳健性也是如此；在这里，我们表明 DH 和 SF 轨迹特别适合这种技术。对于这些轨迹，我们观察到该技术适用于静态和每个投影对齐估计。我们展示了结果，其中 PI 线差异对齐估计与从现有最先进方法获得的对齐估计具有等效的精度：用于静态对齐的断层扫描锐度方法和用于每个投影对齐的重新投影对齐方法。在这两种情况下，