A fast algorithm for computing and correcting the CTF for tilted, thick specimens in TEM

A fast algorithm for computing and correcting the CTF for tilted, thick specimens in TEM

Voortman, L.M.
Stallinga, S.
Schoenmakers, R.H.M.
Van Vliet, L.J.
Rieger, B.

Applied Sciences

IST/Imaging Science and Technology

2011-03-08

Today, the resolution in phase-contrast cryo-electron tomography is for a significant part limited by the contrast transfer function (CTF) of the microscope. The CTF is a function of defocus and thus varies spatially as a result of the tilting of the specimen and the finite specimen thickness. Models that include spatial dependencies have not been adopted in daily practice because of their high computational complexity. Here we present an algorithm which reduces the processing time for computing the ‘tilted’ CTF by more than a factor 100. Our implementation of the full 3D CTF has a processing time on the order of a Radon transform of a full tilt-series. We derive and validate an expression for the damping envelope function describing the loss of resolution due to specimen thickness. Using simulations we quantify the effects of specimen thickness on the accuracy of various forward models. We study the influence of spatially varying CTF correction and subsequent tomographic reconstruction by simulation and present a new approach for space-variant phase-flipping. We show that our CTF correction strategies are successful in increasing the resolution after tomographic reconstruction.

CTF
tilted geometry
nonuniform fast Fourier transform
specimen thickness
TEM
tomography
OA-Fund TU Delft

http://resolver.tudelft.nl/uuid:73f240b2-fe27-4afd-8d99-b766ed09e624

https://doi.org/10.1016/j.ultramic.2011.03.001

Elsevier

0304-3991

http://www.sciencedirect.com/science/article/pii/S0304399111000878

Ultramicroscopy, 111 (8), 2011

Institutional Repository

journal article

(c) 2011 Elsevier