Innovative 3D CTF Correction Techniques for Cryo-ET of Individual Particles

Cryo-electron tomography (Cryo-ET) and subtomogram averaging techniques are highly effective in revealing high-resolution molecular structures. In this technique, accurate Contrast Transfer Function (CTF) correction is essential, as it profoundly affects image quality. This impact arises from various factors, including electron beam characteristics, sample thickness, diffraction phenomena, and lens aberrations. Traditional two-dimensional CTF(2D-CTF) correction methods become inadequate when Cryo-ET is increasingly applied to thicker samples and multi-angle imaging scenarios, since variations in defocus along the tilt axis lead to resolution deterioration. To address this challenge, a novel methodology, termed the Focus Defocus Changes Contrast Transfer Function (FDC-CTF), is put forward as a new type of three-dimensional Contrast Transfer Function (3D-CTF) method. This method geometrically determines the degree of particle defocus based on their coordinates within tomographic slices, effectively tackling the defocus gradient issues induced by sample thickness and tilting. Furthermore, a new workflow is proposed where, after obtaining the particle coordinates, each particle undergoes individual 3D-CTF correction, thereby enhancing the overall accuracy and efficiency of the process. We use two datasets to demonstrate the effectiveness of our method, showcasing its superior performance in alignment accuracy compared to existing methods. It provides a powerful solution for tomographic reconstruction.