Ewald sphere correction using a single side-band image processing algorithm.
Ewald sphere correction using a single side-band image processing algorithm.
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DOI：
10.1016/j.ultramic.2017.11.001
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发表时间：
2018-04
期刊：
影响因子：
2.2
通讯作者：
Henderson R
中科院分区：
文献类型：
--
作者：
Russo CJ;Henderson R
提出了一种修正埃瓦尔德球曲率的方法。我们使用嵌入在冰中的金纳米粒子演示了该算法。该算法自动确定样品的绝对手。它允许在较低的能量下对较厚的样品进行更高分辨率的成像。它还应该改善由cryoEM确定的所有高分辨率结构。埃瓦尔德球的曲率限制了图像中的傅立叶分量可以近似为对应于对象的投影的分辨率。由于埃瓦尔德球的半径是成反比的成像电子的波长，这通常会对样品的厚度施加限制，图像可以很容易地解释到一个特定的分辨率。在这里，我们提出了一种计算方法，用于精确校正的曲率的埃瓦尔德球使用离焦图像，离域的高分辨率傅立叶分量从主图像。通过使用两个不同的复变换来分别校正每个近似傅立叶对称相关的边带，有效地将移位的傅立叶分量移回它们在结构中所属的位置，我们可以分别确定每个傅立叶分量的幅度和相位。这精确地解释了埃瓦尔德球曲率对由散焦和被成像颗粒尺寸定义的带宽的影响。我们证明这种处理算法使用：1。仅具有单个高分辨率傅立叶分量的粒子的模拟图像，以及2.金纳米颗粒嵌入冰中的实验图像。用这种算法处理显微照片将允许在较低的能量下对较厚的标本进行更高分辨率的成像，而不会由于平坦埃瓦尔德球的假设所造成的误差而导致任何图像退化或模糊。虽然该程序将在使用比正常情况下更高的散焦设置记录的图像上工作得最好，但它仍然应该使用在任何散焦和任何电子能量下记录的图像来改善3D单粒子结构测定。最后，由于埃瓦尔德球曲率是在一个已知的方向，在第三个维度，这是平行于观察方向，该算法自动确定的绝对手的标本，而不需要对图像与一个已知的倾斜角差。
A method for correcting for the curvature of the Ewald sphere is presented. We demonstrate the algorithm using gold nanoparticles embedded in ice. The algorithm automatically determines the absolute hand of the specimen. It allows higher resolution imaging of thicker specimens at lower energies. It should also improve all high resolution structures determined by cryoEM. Curvature of the Ewald sphere limits the resolution at which Fourier components in an image can be approximated as corresponding to a projection of the object. Since the radius of the Ewald sphere is inversely proportional to the wavelength of the imaging electrons, this normally imposes a limit on the thickness of specimen for which images can be easily interpreted to a particular resolution. Here we present a computational method for precisely correcting for the curvature of the Ewald sphere using defocused images that delocalise the high-resolution Fourier components from the primary image. By correcting for each approximately Friedel-symmetry-related sideband separately using two distinct complex transforms that effectively move the displaced Fourier components back to where they belong in the structure, we can determine the amplitude and phase of each of the Fourier components separately. This precisely accounts for the effect of Ewald sphere curvature over a bandwidth defined by the defocus and the size of the particle being imaged. We demonstrate this processing algorithm using: 1. simulated images of a particle with only a single, high-resolution Fourier component, and 2. experimental images of gold nanoparticles embedded in ice. Processing micrographs with this algorithm will allow higher resolution imaging of thicker specimens at lower energies without any image degradation or blurring due to errors made by the assumption of a flat Ewald sphere. Although the procedure will work best on images recorded with higher defocus settings than used normally, it should still improve 3D single-particle structure determination using images recorded at any defocus and any electron energy. Finally, since the Ewald sphere curvature is in a known direction in the third dimension which is parallel to the direction of view, this algorithm automatically determines the absolute hand of the specimen without the need for pairs of images with a known tilt angle difference.
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影响因子：
2.2
作者：
Jensen, GJ;Kornberg, RD
通讯作者：
Kornberg, RD
DOI：
10.1098/rsta.2009.0062
发表时间：
2009-09-28
影响因子：
5
作者：
Rose, Harald H.
通讯作者：
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影响因子：
3
作者：
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影响因子：
3
作者：
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通讯作者：
Grigorieff, Nikolaus
影响因子：
2.2
作者：
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通讯作者：
Cernetic, Laslo