McLeod Robert A, Kowal Julia, Ringler Philippe, Stahlberg Henning
Center for Cellular Imaging and NanoAnalytics, Biozentrum, Universität Basel, Basel, Switzerland.
Center for Cellular Imaging and NanoAnalytics, Biozentrum, Universität Basel, Basel, Switzerland.
J Struct Biol. 2017 Mar;197(3):279-293. doi: 10.1016/j.jsb.2016.12.006. Epub 2016 Dec 27.
Cryo-electron microscopy recently experienced great improvements in structure resolution due to direct electron detectors with improved contrast and fast read-out leading to single electron counting. High frames rates enabled dose fractionation, where a long exposure is broken into a movie, permitting specimen drift to be registered and corrected. The typical approach for image registration, with high shot noise and low contrast, is multi-reference (MR) cross-correlation. Here we present the software package Zorro, which provides robust drift correction for dose fractionation by use of an intensity-normalized cross-correlation and logistic noise model to weight each cross-correlation in the MR model and filter each cross-correlation optimally. Frames are reliably registered by Zorro with low dose and defocus. Methods to evaluate performance are presented, by use of independently-evaluated even- and odd-frame stacks by trajectory comparison and Fourier ring correlation. Alignment of tiled sub-frames is also introduced, and demonstrated on an example dataset. Zorro source code is available at github.com/CINA/zorro.
由于具有改进对比度和快速读出功能的直接电子探测器实现了单电子计数，低温电子显微镜最近在结构分辨率方面有了很大提高。高帧率实现了剂量分馏，即将长时间曝光分解为一部电影，从而能够记录并校正样本漂移。对于具有高散粒噪声和低对比度的图像配准，典型方法是多参考（MR）互相关。在此，我们展示了软件包Zorro，它通过使用强度归一化互相关和逻辑噪声模型对MR模型中的每个互相关进行加权并对每个互相关进行最佳滤波，从而为剂量分馏提供强大的漂移校正。Zorro能够以低剂量和散焦可靠地配准帧。通过轨迹比较和傅里叶环相关，利用独立评估的偶数帧和奇数帧堆栈，展示了评估性能的方法。还介绍了平铺子帧的对齐，并在一个示例数据集上进行了演示。Zorro源代码可在github.com/CINA/zorro获取。
