X光发散度对多切片扫描相干衍射成像质量的影响

Effects of the probe divergence degree on the imaging quality of multi-slice 3D ptychography

扫描相干衍射成像(Ptychography)技术目前已得到大范围的应用,获得了巨大成功。基于Ptychography的三维成像技术也得到了快速发展,在生物和材料领域的研究中得到了成功应用。常规的Ptychography三维成像技术仍是基于多角度投影的计算机断层成像技术,具有成像效率低、辐照剂量大的缺点。最近出现的多切片三维Ptychography成像方法,为高效低剂量的三维成像技术开辟了新的道路。为了进一步改善多切片方法的重建效率和图像质量,本文在优化迭代算法中驰豫系数的基础上,通过模拟计算系统地研究了入射X射线的发散度对多切片方法重建效果的影响。结果表明:入射X射线的发散度越高(数值孔径越高),多切片方法图像迭代重建的收敛越快,图像的重建质量也更好;而选择较小的入射X光发散度则不利于三维成像的高质量重建。该结论对于相关成像实验中聚焦光学的选择和设置具有重要的指导意义,如选择聚焦尺寸更小的波带片或较低的入射X射线能量,将更有希望获得好的多切片成像质量。

[Background] Ptychography technology has been applied widely nowadays, and has made great achievements in the fields of materials, energy and life sciences. Traditional Ptychography 3D imaging is based on the computational tomography technology with multi-angular projection which has the disadvantages of lowefficiency and high-dose. The emerging multi-slice 3D imaging approach opens up a new way for high-efficiency low-dose 3D imaging.[Purpose] This study aims to improve the reconstruction convergence and imaging quality of the multi-slice ptychographic tomography with emphasis on the effect of the illumination divergence degree on the reconstructed image of this approach.[Methods] First of all, a numerical simulation method was employed to optimize the relaxation parameters. Then the effect of divergence of incident X-ray on reconstruction quality of multislice method was investigated by simulation experiments. Finally, the reconstructed images were compared directly with the ground-truth original images, and an error metric was calculated for monitoring the convergence of the reconstruction and measuring the quality of the reconstructed image.[Results] It was found that the higher the divergence degree of the incident beam, the faster the iterative reconstruction converges, and the better the reconstructed image quality.[Conclusion] The choice and setting of the focusing optical devices are significant in multi-slice ptychographic tomography experiments, a zone-plate with a smaller outermost zone width or an X-ray beam with lower energy in such experiments are helpful to obtain a better imaging quality by using multi-slice 3D ptychography approach.