1. A system for registering images comprising an image registration unit, said image registration unit comprising non-transitory executable code that, when executed by the registration unit, causes the registration unit to: receive first image data for a first image in an N-dimensional space; receive second image data for a second image in said N-dimensional space; calculate a field of update vectors that maps said first image into a moving image; and map said first image into said moving image using said field of update vectors such that said moving image more closely matches said second image, wherein said field of update vectors comprises a plurality of N+M dimensional update vectors, each update vector having N spatial components and M extra components, wherein N is a number greater than zero, wherein M is a number greater than zero, and wherein said M extra components of said plurality of update vectors identify portions of said first image that are assigned external values during said mapping said first image into said moving image.