Towards continuous time-dependent tomography: implementation and evaluation of continuous acquisition schemes in electron tomography

Abstract

Electron tomography is a microscopy technique that allows the three-dimensional (3D) characterization of nanomaterials by reconstructing a 3D volume from a series of two-dimensional (2D) projection images acquired at different viewing angles. In a transmission electron microscope (TEM), the change in angle is achieved by tilting the sample holder and conventionally follows an incremental tilt scheme. Images are typically acquired between $\pm$ 60–80°, as dictated by the TEM geometry, and in small, 2–3°, increments to minimize sample shifts and facilitate acquisition and post-processing. This tilt scheme unfortunately performs poorly when time resolution is necessary, i.e., when as many 3D reconstructions as possible of the same object within a given time are desired. Golden ratio scanning (GRS) and binary decomposition (BD) have been proposed in other tomographies because they allow consecutive reconstructions to share some projections. However, due to practical considerations, they have seen limited usage in electron tomography. In this work, we present optimized implementations of GRS and BD for electron tomography with corrections for alignment, backlash, and angular uniformity. These tilt schemes were compared with incremental acquisition for simulated and experimental datasets in static or dynamic contexts. Experimentally, GRS and BD required 2–3 times longer acquisition time, and resulted in a 2 times increase in electron dose compared to the incremental scheme, thus confirming the incremental scheme as the method to be favored for static applications. In dynamic applications, our results suggest that a time vs. spatial resolution tradeoff should be considered. Nonetheless, GRS and BD schemes would achieve up to 30x higher 3D frame rate, showing promise toward time-dependent electron tomography.