Non-rigid medical image registration based on improved Demons algorithm

Non-rigid registration is one of the important research issues in medical image processing field.An intensity-based automatic deformable image registration algorithm,known as the "Demons" algorithm,only depends on the image intensity gradients of the reference image to drive the floating image transform,it easily results in wrong registration when gradients are small,even being zeros.Moreover,this algorithm is not fit for the registration of multi-modality images.So,an improved "Demons" algorithm is proposed in this paper.The method adds additional external force based on the fact that the two images can make the mutual information between them maximal,and the force is defined as the gradient of mutual information between the two images with respect to the deformation field.Moreover,to avoid local extrema and speed up the registration process,the algorithm is performed in a multi-resolution manner.Experiments are conducted with both mono-modality and multi-modality images,the results show that this improved method can get a accurate registration transformation quickly.