Basic Definition:
A voxel is the smallest addressable element in a three-dimensional digital volume (ASTM-E 1316-22). This can be thought of as a three-dimensional pixel: a “volume element” in the same sense that a pixel is a picture element (element of a 2D image). With respect to a CT scan, voxels are essentially the building blocks of the scan volume. Each voxel has known X, Y, and Z dimensions, and is assigned a single grayscale value or Hounsfield Unit that corresponds to the average attenuation of all materials contained within the voxel.