Optimal and automated mask alignment for use in edge illumination X-ray differential-phase and dark-field imaging techniques
Optimal and automated mask alignment for use in edge illumination X-ray differential-phase and dark-field imaging techniques
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DOI：
10.1016/j.nima.2020.164602
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发表时间：
2020-12-21
影响因子：
1.4
通讯作者：
Endrizzi, Marco
中科院分区：
文献类型：
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作者：
Doherty, Adam;Massimi, Lorenzo;Endrizzi, Marco
边缘照明X射线相衬成像利用两个吸收掩模进行精确的光束整形和分析。由于该系统正在被转换到临床和工业环境中，因此需要一种强大的定量算法来保持掩模精确对准，而不需要专业操作员。我们提出了一个模型，如何在检测器上的照明变化作为一个掩模相对于系统的其余部分移动。该模型基于与每个自由度中的未对准相关联的已知照明图案的叠加。通过对该模型的反演，可以定量地估计失准程度，从而给出最佳对准位置。通过模型反演实现的对准精度进行了测试，显示出至少一个数量级的改善相比，建立掩模对准程序。发现沿光轴沿着和围绕三个旋转自由度的对准精度分别为[+/- 0.78 μ m，+/- 0.17 mdeg，+/- 5.08 mdeg，+/- 2.39 mdeg]，而建立的过程将限于[+/- 42.5 μ m，+/- 6.69 mdeg，+/- 348 mdeg，+/- 195毫度]。此外，该模型允许将残差分解为随机和系统分量，后者能够准确评估掩模结构中的缺陷，这些缺陷现在已成为最终对准程度的主要限制因素。
Edge illumination X-ray phase-contrast imaging makes use of two absorbing masks for precise beam shaping and analysis. As the system is being translated to clinical and industrial environments, a robust quantitative algorithm is required to keep the masks precisely aligned without the need of an expert operator. We present a model for how the illumination on the detector varies as one mask is moved relative to the rest of the system. This model is based on a superposition of known illumination patterns associated with misalignment in each degree of freedom. Through inversion of this model, quantitative estimates of the degree of misalignment can be obtained, and hence can show the position of optimal alignment. The precision of alignment achievable through model inversion was tested, showing at least an order of magnitude improvement when compared to the established mask alignment procedure. Precision of the alignment along the optical axis, and around the three rotational degrees of freedom were found to be [+/- 0.78 mu m, +/- 0.17 mdeg, +/- 5.08 mdeg, +/- 2.39 mdeg] respectively, whereas the established procedure would be limited to [+/- 42.5 mu m, +/- 6.69 mdeg, +/- 348 mdeg, +/- 195 mdeg]. Furthermore, the model allows the decomposition of residuals into random and systematic components, the latter enabling accurate evaluation of imperfections in the masks' structure which have now become the main limiting factor in the final degree of alignment.