Robisch Anna-Lena, Eckermann Marina, Töpperwien Mareike, van der Meer Franziska, Stadelmann Christine, Salditt Tim
Georg-August-Universität Göttingen, Institut für Röntgenphysik, Göttingen, Germany.
University of Göttingen, Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells," Göttingen, Germany.
J Med Imaging (Bellingham). 2020 Jan;7(1):013501. doi: 10.1117/1.JMI.7.1.013501. Epub 2020 Jan 22.
X-ray cone-beam holotomography of unstained tissue from the human central nervous system reveals details down to subcellular length scales. This visualization of variations in the electron density of the sample is based on phase-contrast techniques using intensities formed by self-interference of the beam between object and detector. Phase retrieval inverts diffraction and overcomes the phase problem by constraints such as several measurements at different Fresnel numbers for a single projection. Therefore, the object-to-detector distance (defocus) can be varied. However, for cone-beam geometry, changing defocus changes magnification, which can be problematic in view of image processing and resolution. Alternatively, the photon energy can be altered (multi-E). Far from absorption edges, multi-E data yield the wavelength-independent electron density. We present the multi-E holotomography at the Göttingen Instrument for Nano-Imaging with X-Rays (GINIX) setup of the P10 beamline at Deutsches Elektronen-Synchrotron. The instrument is based on a combined optics of elliptical mirrors and an x-ray waveguide positioned in the focal plane for further coherence, spatial filtering, and high numerical aperture. Previous results showed the suitability of this instrument for nanoscale tomography of unstained brain tissue. We demonstrate that upon energy variation, the focal spot is stable enough for imaging. To this end, a double-crystal monochromator and automated alignment routines are required. Three tomograms of human brain tissue were recorded and jointly analyzed using phase retrieval based on the contrast transfer function formalism generalized to multiple photon energies. Variations of the electron density of the sample are successfully reconstructed.
对来自人类中枢神经系统的未染色组织进行X射线锥束全息断层扫描可揭示直至亚细胞长度尺度的细节。这种对样品电子密度变化的可视化基于相衬技术，该技术利用物体与探测器之间光束自干涉形成的强度。相位恢复可反转衍射，并通过诸如对单个投影在不同菲涅耳数下进行多次测量等约束来克服相位问题。因此，物体到探测器的距离（散焦）可以变化。然而，对于锥束几何结构，改变散焦会改变放大倍数，这在图像处理和分辨率方面可能会有问题。或者，可以改变光子能量（多能量）。在远离吸收边缘的情况下，多能量数据可产生与波长无关的电子密度。我们展示了在德国电子同步加速器P10光束线的哥廷根纳米成像X射线装置（GINIX）设置下的多能量全息断层扫描。该仪器基于椭圆镜和位于焦平面的X射线波导的组合光学系统，用于进一步的相干性、空间滤波和高数值孔径。先前的结果表明该仪器适用于未染色脑组织的纳米级断层扫描。我们证明，在能量变化时，焦斑足够稳定以进行成像。为此，需要一个双晶单色仪和自动对准程序。记录了三张人类脑组织的断层图像，并使用基于推广到多个光子能量的对比度传递函数形式的相位恢复进行联合分析。成功重建了样品电子密度的变化。
