CTF determination and correction for low dose tomographic tilt series.
CTF determination and correction for low dose tomographic tilt series.
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DOI：
10.1016/j.jsb.2009.08.016
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发表时间：
2009-12
影响因子：
3
通讯作者：
Mastronarde, David N.
中科院分区：
文献类型：
--
作者：
Xiong, Quanren;Morphew, Mary K.;Schwartz, Cindi L.;Hoenger, Andreas H.;Mastronarde, David N.
低温电子断层扫描的分辨率可能受到显微镜对比度传递函数（CTF）的第一个零点的限制。为了获得更高的分辨率，确定CTF并校正其相位反转是至关重要的。然而，极低的信噪比（SNR）和倾斜标本的投影中的散焦梯度使这个过程具有挑战性。两个程序，CTFPLOTTER和CTFPHASEFLIP，已经开发出来，以解决这些问题。CTFPLOTTER通过周期图平均和旋转平均获得一维功率谱，并采用一种新的方法估计噪声背景，该方法使用无样本拍摄的图像。然后，来自不同散焦值的图像区域的背景扣除的1D功率谱被移位以对齐它们的第一个零并一起平均。这种平均充分地改善了SNR，使得可以确定倾斜系列的子集而不是整个系列的散焦。CTFPHASEFLIP通过在几乎恒定的散焦下适当地反转图像的细条中的相位来逐行校正图像。通过这些方法的CTF校正被示出为提高从断层图像中提取的对齐的平均颗粒的分辨率。然而，在高频处傅立叶振幅的一些恢复对于看到CTF校正的益处是重要的。
The resolution of cryo-electron tomography can be limited by the first zero of the microscope’s contrast transfer function (CTF). To achieve higher resolution, it is critical to determine the CTF and correct its phase inversions. However, the extremely low signal-to-noise ratio (SNR) and the defocus gradient in the projections of tilted specimens make this process challenging. Two programs, CTFPLOTTER and CTFPHASEFLIP, have been developed to address these issues. CTFPLOTTER obtains a 1D power spectrum by periodogram averaging and rotational averaging and it estimates the noise background with a novel approach, which uses images taken with no specimen. The background-subtracted 1D power spectra from image regions at different defocus values are then shifted to align their first zeros and averaged together. This averaging improves the SNR sufficiently that it becomes possible to determine the defocus for subsets of the tilt series rather than just the entire series. CTFPHASEFLIP corrects images line-by-line by inverting phases appropriately in thin strips of the image at nearly constant defocus. CTF correction by these methods is shown to improve the resolution of aligned, averaged particles extracted from tomograms. However, some restoration of Fourier amplitudes at high frequencies is important for seeing the benefits from CTF correction.
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影响因子：
2.2
作者：
Fernandez, J. J.;Li, S.;Crowther, R. A.
通讯作者：
Crowther, R. A.
影响因子：
3
作者：
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影响因子：
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作者：
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影响因子：
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作者：
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影响因子：
2
作者：
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通讯作者：
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