The second criterion is the smoothness of the estimated MVF for the floating image and evaluated at [x.sub.i] by the Frobenius norm of a Hessian matrix using the next equation
In our previous RSM, the similarity of the image intensity distribution and the smoothness of the MVF were used.
Thus the MVF is constrained in angle but not in magnitude.
As feature points for getting the MVF of CT images, 13 bifurcation points were selected and used.
The proposed RSM was applied to a numerical phantom and clinical BH-PET images and compared with our previous RSM which used only the similarity of the image intensity distribution and the smoothness of MVF as optimization criteria.