The principal axes transformation--a method for image registration.

We have developed a computational technique suitable for registration of sets of image data covering the whole brain volume which are translated and rotated with respect to one another. The same computational method may be used to register pairs of tomographic brain images which are rotated and translated in the transverse section plane. The technique is based on the classical theory of rigid bodies, employing as its basis the principal axes transformation. The performance of the method was studied by simulation and with image data from PET, XCT, and MRI. It was found that random errors in determining the brain contour are well tolerated. Progressively coarser axial sampling of data sets led to some degradation, but acceptable performance was obtained with axial sampling distances up to 10 mm. Given adequate digital sampling of the object volume, we conclude that registration by the principal axes transformation can be accomplished with typical errors in the range of approximately 1 mm. The advantages of the technique are simplicity and speed of computation.