“…The theoretical basis of information theory is: The information reflected in the two images must have some intrinsic association, with the change in the matching degree of the two images, this correlation also changes. Mutual information can qualitatively be thought of as a measureof how well one image explains the other, and is maximized at the optimal alignment[4,5]. The maximization of mutual information[6], as a kind of information theory method for similarity metric, needs not to conduct segmenting or pretreatment to images nor limit treated contents, which has better precision and higher stability compared with other methods based on voxel similarity[7,8].…”