Table 1.

Glossary of terms

High-pressure freezing	Method for freezing large volumes of tissue that depends on application of high pressures to prevent formation of ice crystals.
Freeze-substitution	Ice in frozen tissue is replaced with an organic solvent, thereby introducing stabilizing molecules and heavy metal stains into the tissue.
Fiducial marker	Gold particles applied to sections to aid fine alignment of a set of tilted images.
Projection angle	Complement of the angle between the specimen plane and the incoming electron beam.
Backprojection	Reverse of projection to yield a 3D reconstruction, or tomogram, from a set of tilted images.
Missing pyramid	Blind spot in two axis tomographic series attributable to limitations in tilt angle, leading to a loss of resolution in the final tomogram.
Tomogram	Computed 3D volume based on backprojections of all images from a tilt series.
Virtual section	Any individual section computed from a tomogram whose minimum thickness is one 3D pixel, or voxel.