In a context of automation of cryo-electron microscopy, we developed a novel method for improving visibility of diffraction rings in the power spectra of cryo-electron micrographs of vitreous ice (without carbon film or high concentration of diffracting material). We used these enhanced spectra to semi-automatically detect and remove micrographs and/or local areas introducing errors in the global 3D map (drifted and charged areas) or those unable to increase global signal-to-noise ratio (non-diffracting areas). Our strategy also allows a detection of micrographs/areas with a strong astigmatism. These images should be removed when using algorithms that do not correct astigmatism. Our sorting method is simple and fast since it uses the normalized cross-correlation between enhanced spectra and their copies rotated by 90 degrees. It owes its success mainly to the novel pre-processing of power spectra. The improved visibility also allows an easier visual check of accuracy of sorting. We show that our algorithm can even improve the visibility of diffraction rings of cryo-electron micrographs of pure water. Moreover, we show that this visibility depends strongly on ice thickness. This algorithm is implemented in the Xmipp (open-source image processing package) and is freely available for implementation in any other software package.

译文

:在低温电子显微镜自动化的背景下,我们开发了一种新颖的方法,用于改善玻璃冰(无碳膜或高浓度衍射材料)的低温电子显微镜照片的功率谱中衍射环的可见性。我们使用这些增强的光谱来半自动检测和移除显微照片和/或局部区域,从而在全局3D地图(漂移和带电区域)或无法增加全局信噪比(非衍射区域)的区域引入误差。我们的策略还允许检测具有强烈散光的显微照片/区域。当使用无法校正像散的算法时,应删除这些图像。我们的排序方法简单而快速,因为它使用了增强频谱与其旋转90度的副本之间的归一化互相关。它的成功主要归功于新颖的功率谱预处理。改进的可见性还可以使目视检查的准确性更加容易。我们证明了我们的算法甚至可以提高纯水冷冻电子显微照片的衍射环的可见性。此外,我们证明了这种能见度在很大程度上取决于冰的厚度。该算法在Xmipp(开源图像处理软件包)中实现,可免费用于任何其他软件包中。

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