A method for registering a first image and a second image, wherein said first image comprise data significant for x-ray attenuation from a first medical imaging study and said second image comprise data significant for x-ray attenuation from at least a second medical imaging study, the method comprises obtaining a first tissue class first subimage associated with said first image and comprising information of a first tissue class in said first image, obtaining a first tissue class second subimage associated with said second image and comprising information of said first tissue class in said second image, wherein the first tissue class is bone tissue; a first registration of said first image to said second image, wherein said first registration comprises optimization of a first weighted cost function, said first weighted cost function comprising the sum of a correlation of the first image to the second image with a first weight factor of said first registration; and a correlation of said first tissue class first subimage to said first tissue class second subimage with a second weight factor of said first registration, said first and second weight factors of said first registration are nonzero; wherein a first set of deformation parameters from said first registration associated with a transformation of said first image to said second image are obtained from said optimization, and a second registration of said first image to said second image, wherein said second registration comprises correlation of at least part of said first image to at least part of said second image based on said first set of deformation parameters, wherein a second set of deformation parameters associated with a transformation of said first image to said second image are obtained from said correlation. obtaining a first tissue class first subimage associated with said first image and comprising information of a first tissue class in said first image, obtaining a first tissue class second subimage associated with said second image and comprising information of said first tissue class in said second image, wherein the first tissue class is bone tissue; a first registration of said first image to said second image, wherein said first registration comprises optimization of a first weighted cost function, said first weighted cost function comprising the sum of a correlation of the first image to the second image with a first weight factor of said first registration; and a correlation of said first tissue class first subimage to said first tissue class second subimage with a second weight factor of said first registration, said first and second weight factors of said first registration are nonzero; wherein a first set of deformation parameters from said first registration associated with a transformation of said first image to said second image are obtained from said optimization, and optimization of a first weighted cost function, said first weighted cost function comprising the sum of a correlation of the first image to the second image with a first weight factor of said first registration; and a correlation of said first tissue class first subimage to said first tissue class second subimage with a second weight factor of said first registration, said first and second weight factors of said first registration are nonzero; a correlation of the first image to the second image with a first weight factor of said first registration; and a correlation of said first tissue class first subimage to said first tissue class second subimage with a second weight factor of said first registration, said first and second weight factors of said first registration are nonzero; wherein a first set of deformation parameters from said first registration associated with a transformation of said first image to said second image are obtained from said optimization, and a second registration of said first image to said second image, wherein said second registration comprises correlation of at least part of said first image to at least part of said second image based on said first set of deformation parameters, wherein a second set of deformation parameters associated with a transformation of said first image to said second image are obtained from said correlation.