Whole Body Medical Image Registration

It seems that whole body medical image registrtion is solved already as the researchers claimed in the publications. MI and B-spline are used in my test, the LBFGS optimization is employed in the process. CT-CT image can be aligned well, but when the algorithm is used to solve PET-CT image registration, the result is not good enough, even can not be accepted. I can not draw a conclusion the classical method can not solve these kind of problems because this is a primary test. The gobal rigid and local norigid registration may be combined together for the problem. Another issue we should pay attention is the images volume are 3D and the multi-resolution stretegy can improve the computation speed.