Expanding horizons of cryo-tomography to larger volumes

The three dimensional ultrastructure of cells and tissues comes to light with tomography. There is an inherent tension between representing molecular detail at the highest possible resolution, on one hand, and visualizing spatial relations between large organelles or even neighboring cells in large volumes, on the other. Together with its advantages for pristine sample preservation, cryo-tomography brings particular constraints. A major challenge has been the restriction to specimens thinner than the typical cell. New imaging modalities are now available to extend cryo-tomography to thicker specimens: cryo-scanning transmission electron tomography (CSTET), soft X-ray tomography (SXT), and serial surface imaging using the focused ion beam-scanning electron microscope (FIB-SEM). Each one offers specific advantages so the optimal choice depends on priorities among resolution, composition, and volume.