Key Laboratory for Protein Sciences of Ministry of Education, School of Life Sciences, Tsinghua University, Beijing 100084, China; State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Joint Center for Life Sciences, Beijing 100084, China; Beijing Frontier Research Center for Biological Structure, Beijing 100084, China; School of Life Sciences, Tsinghua University, Beijing 100084, China; Department of Electronic Engineering, Tsinghua University, Beijing 100084, China; Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing 100084, China.
Department of Electronic Engineering, Tsinghua University, Beijing 100084, China; Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing 100084, China.
Structure. 2024 Aug 8;32(8):1239-1247.e3. doi: 10.1016/j.str.2024.05.006. Epub 2024 May 31.
Contrast transfer function (CTF) estimation is a necessary step in the cryo-electron tomography (cryoET) workflow and essential for high-resolution in situ structural determination. However, the low signal-to-noise ratio and continuous defocus variation in micrographs of cryoET tilt series make accurate CTF estimation challenging. Here, we report a tilt-series-based joint CTF estimation method implemented in the new software CTFMeasure. The joint estimation method combines all Thon-ring signals in a tilt series to improve the estimation accuracy. By using an objective function involving the CTF parameters and geometric parameters of a cryoET tilt series, CTFMeasure can estimate the CTF parameters of each micrograph and the absolute tilt angle offset of the lamellar sample relative to the sample stage plane, which is usually the glancing angle used during focused ion beam (FIB) milling. Tests on both synthetic and experimental data, as well as subtomogram averaging, demonstrated the accurate CTF estimation of cryoET tilt series by CTFMeasure.
对比度传递函数（CTF）估计是低温电子断层扫描（cryoET）工作流程中的必要步骤，对于高分辨率的原位结构测定至关重要。然而，cryoET 倾斜系列显微照片中的信噪比低且连续的离焦变化使得准确的 CTF 估计具有挑战性。在这里，我们报告了一种基于倾斜系列的联合 CTF 估计方法，该方法在新软件 CTFMeasure 中实现。联合估计方法结合了倾斜系列中的所有 Thon 环信号，以提高估计的准确性。通过使用涉及 CTF 参数和 cryoET 倾斜系列几何参数的目标函数，CTFMeasure 可以估计每个显微照片的 CTF 参数以及相对于样品台平面的层状样品的绝对倾斜角度偏移，该角度通常是聚焦离子束（FIB）铣削过程中使用的掠射角。对合成数据和实验数据以及子断层平均的测试表明，CTFMeasure 可以准确估计 cryoET 倾斜系列的 CTF。
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