tiltseries

A tilt series is a sequence of two-dimensional images of a specimen acquired at progressively different tilt angles with respect to the imaging axis, typically collected in electron tomography using a transmission electron microscope. The series is used to reconstruct a three-dimensional volume of the sample, revealing its internal organization beyond what a single projection can show.

In practice, the specimen is tilted about a defined axis while images are recorded at discrete angles. Typical tilt ranges extend from about -60 to +60 degrees, or -70 to +70 degrees for more coverage, with angular steps of 1–2 degrees (sometimes smaller). Electron dose is managed by distributing exposure across tilts, and defocus is adjusted to optimize contrast for the data being collected. Fiducial markers or features within the specimen facilitate subsequent alignment.

Alignment and reconstruction are core steps. Fiducial markers such as gold beads or feature-based tracking are used to align images into a common reference frame. Tomographic reconstruction then combines the aligned projections using methods such as weighted back projection, simultaneous iterative reconstruction technique (SIRT), or other iterative algorithms. A common limitation is the missing wedge created by an incomplete tilt range, which produces anisotropic resolution along the axis perpendicular to the tilt axis; strategies like dual-axis tomography or extending the tilt range help mitigate this effect.

Variations include dose-symmetric tilt schemes that balance dose across tilts and continuous tilt acquisitions. Processing and visualization are supported by software packages such as IMOD, Dynamo, and Eman, as well as cryo-electron tomography workflows.

Applications of tilt-series tomography span structural biology, materials science, and related fields, enabling three-dimensional insight into cellular architecture, nanostructures, and composite materials.