Multimodality imaging studies are becoming more widely utilized in the analysis of medical data. Anatomical data from computed tomography (CT) and magnetic resonance imaging (MRI) are useful for analyzing or further processing functional data from techniques such as positron emission tomography and single photon emission computed tomography (SPECT). When data are not acquired simultaneously, even when these data are acquired on a dual-imaging device using the same bed, motion can occur that requires registration between the reconstructed image volumes. As the human torso can allow nonrigid motion, this type of motion should be estimated and corrected. The authors report a deformation registration technique that utilizes rigid registration for bony structures while allowing elastic transformation of soft tissue to more accurately register the entire image volume. The technique is applied to the registration of CT and MR images of the lumbar spine.