Defocus estimation from stroboscopic cryo-electron microscopy data

Defocus estimation is an important step for improving the resolution of single particle reconstructions. It can be troublesome to estimate the defocus from low-dose cryo-electron microscopy (cryo-EM) data, particularly if there is not sufficient contrast present in the Fourier transform of the micrograph. Most existing approaches estimate the defocus from the presence of Thon rings within the power spectrum, employing image enhancement techniques to highlight these rings. In this paper, an approach to estimating the defocus from a stroboscopic image series is described. The image series is used to obtain two statistical metrics: figure of merit (FOM) and Q-factor. These metrics have been used to estimate the defoci from low-dose stroboscopic cryo-EM data consisting of a variable number of images.

► Defocus estimation from stroboscopic cryo-electron microscopy (cryo-EM) data. ► Figure of merit (FOM) defined as the average cosine of phase errors. ► FOM and Q-factor enables the estimation of defocus from low-dose cryo-EM images. ► FOM and Q-factor provide a metric of the quality of cryo-EM data.