A voxel is to a 3D image as a pixel is to a flat 2D image. It is a measure of space.
This matters if you are considering a come beam CT. The CBCT will render the image in voxels. As a general rule the smaller the voxel size the more detail (or resolution) the image can present. However, as is often the case, it just isn’t that simple. There are many other factors which will determine the resolution and the clarity of a CBCT image.
These other factors range from how tightly the patient’s head is held in place to the proprietary internal software in the machine that creates the voxel to begin with.
For more information visit Cone Beam Guru Dale Miles.