A voxel is a 3-dimentional pixel, with an X, Y, and Z value. The X and Y values are always equal. The UChicago PaleoCT machine is isotropic, meaning the X, Y and Z dimensions are always equal, but in some machines, particularly in medical CT machines, the Z dimension may be different. These dimensions are determined by the position of the specimen in the machine and are listed in the .pca file or other files associated with the scan data.