Signal enhancement and Patterson-search phasing for high-spatial-resolution coherent X-ray diffraction imaging of biological objects

Abstract

In this decade coherent X-ray diffraction imaging has been demonstrated to reveal internal structures of whole biological cells and organelles. However, the spatial resolution is limited to several tens of nanometers due to the poor scattering power of biological samples. The challenge is to recover correct phase information from experimental diffraction patterns that have a low signal-to-noise ratio and unmeasurable lowest-resolution data. Here, we propose a method to extend spatial resolution by enhancing diffraction signals and by robust phasing. The weak diffraction signals from biological objects are enhanced by interference with strong waves from dispersed colloidal gold particles. The positions of the gold particles determined by Patterson analysis serve as the initial phase, and this dramatically improves reliability and convergence of image reconstruction by iterative phase retrieval. A set of calculations based on current experiments demonstrates that resolution is improved by a factor of two or more.

Cryogenic coherent X-ray diffraction imaging of biological samples at SACLA: a correlative approach with cryo-electron and light microscopy

“…The top 100 reconstructions that best represented the group were averaged and used to refine the support. When starting from the support determined by Patterson-search phasing, the PR calculations converged to a well defined solution, and this case did not need PCA as previously reported (Takayama, Maki-Yonekura et al, 2015).…”

“…Note that the color scale in (g) is three times higher than that in (d) owing to the high projected electron density of the CG particles. Takayama, Maki-Yonekura et al, 2015). In the map, correct peaks are found at positions of CG particles, but false peaks that arise from the 'fringes' in (c) also appear around the correct peaks.…”

“…We proposed a method to extend the spatial resolution by imaging biological objects together with colloidal gold (CG) particles (Takayama, Maki-Yonekura et al, 2015). Weak signals from biological objects can be enhanced to a detectable level by interference with strong diffraction waves from the CGs (Shintake, 2008(Shintake, , 2010Takayama, Maki-Yonekura et al, 2015).…”

“…We then applied the Patterson-search phasing method (Takayama, Maki-Yonekura et al, 2015) to these patterns (Figs. 7a and 7b) and successfully solved the sharpened Patterson maps (Fig.…”

Cryo-coherent diffractive imaging of biological samples with X-ray free-electron lasers

“…Takayama and Yonekura (Takayama & Yonekura, 2016;Takayama et al, 2015) report an effective strategy for combining frozen-hydrated sample preparation with XFEL-CDI while maintaining the hydrated state of the sample, using a special experimental setup at the SACLA XFEL light source. Additionally, specific control and data-processing software [the G-SITENNO suite Sekiguchi, Yamamoto et al, 2014)] has been developed, which enables automatic background subtraction, merging of high-and low-resolution diffraction patterns, and display of the diffraction patterns.…”