Validation of 3D cryoEM single particle reconstruction correctness and handedness with Ewald's sphere correction

Abstract

The correct description of quantum scattering places the observed scattering contributions on the Ewalds sphere and its Friedel mate copy. In electron microscopy, due to the large radius of the Ewalds sphere, these scattering contributions are typically merged during data analysis. We present an approach that separates and factorizes those contributions into real and imaginary components of the image. When an inverted solution is calculated, the map derived from the real component of the image generates an inverted solution, while the map derived from the imaginary component of the image generates an inverted and sign-flipped solution. Therefore, the sign of correlation between reconstructions derived from the real and imaginary components provides the automatic determination of handedness and additional validation for the quality of 3D reconstructions. The factorization and its implementation are robust enough to be routinely used in single-particle reconstructions, even at resolutions below the limit where the curvature of the Ewalds sphere affects the overall signal-to-noise ratio.