Tomography

The complex and dynamic organization of cells exists in three dimensions, posing a challenge for conventional TEM, which provides only two-dimensional images of inherently three-dimensional objects. Electron tomography is a powerful technique that overcomes this limitation by combining a large number of 2D images of the object computationally, resulting in detailed 3D structures that enable analysis of cellular architecture in three dimensions.

Basic theory and principles of electron tomography

In electron tomography, a biological sample is imaged from multiple angles by tilting the sample holder around an axis perpendicular to the electron beam (ranging from -70⁰ to +70⁰). Single projection images are captured at different angles, and these images are then precisely aligned and combined in either real or reciprocal space to generate a comprehensive three-dimensional reconstruction volume. This reconstructed volume can be further analysed using software tools to create graphic models of the specimen by segmenting different structures into distinct objects.

Image 1: Schematic of sample tilting and image acquisition	Image 2: Schematic of tomographic reconstruction

Sample preparation

Sample preparation for electron tomography follows a similar process to that of conventional TEM, with the exception of section thickness. Electron tomography sections are typically thicker, ranging from 200nm to 300nm, allowing for the recording and reconstruction of larger volumes.