Quantitative phase imaging of single particles from a cryoEM micrograph

TL;DR

This paper introduces a novel method for extracting quantitative phase information from de-focused cryoEM images of single particles, enabling improved analysis by correcting for defocus and aberrations using phase retrieval techniques.

Contribution

It presents a new phase retrieval approach that treats cryoEM images as Fresnel holograms, allowing accurate phase mapping and correction of defocus and aberrations in single particle analysis.

Findings

Effective phase retrieval from de-focused cryoEM images.

Applicable to both CCD and direct electron detectors.

Improves accuracy of single particle phase information.

Abstract

We show that de-focused single particle images recorded using a cryo-electron microscope (cryoEM) system may be processed like a Fresnel zone in-line hologram to obtain physically meaningful quantitative phase maps associated with individual particles. In particular, a region-of-interest (ROI) of the de-focused image surrounding a particle can be numerically back-propagated, in order to determine accurate de-focus information based on the sparsity-of-gradient merit function. Further with the knowledge of de-focus information, an iterative Fresnel zone phase retrieval algorithm using image sparsity constraints can accurately estimate the quantitative phase information associated with a single particle. The proposed methodology which can correct for both de-focus and spherical aberrations is a deviation from the image processing chain currently used in single particle cryoEM reconstructions. Our illustrations as presented here suggest that the phase retrieval approach applies uniformly to de-focused image data recorded using the traditional CCD detectors as well as the newer direct electron detectors.