Abstract: To solve the problem that the object function is easy to get into local optimalization because of much local extremes in the mutual information registration method,a mutual information medical image registration algorithm based on firefly algorithm was put forward．The normalized mutual information is used as the similarity measure and registration parameters are expressed by the locations of fireflies in the algorithm,and mutual information function values are calculated according to the locations of fireflies and are set as brightness values of fireflies,and the best registration parameters are retrieved by updating the brightness and attractiveness iteratively while the mutual information function reaches the maximum value．The experimental results indicate that this algorithm can effectively overcome the problem that the mutual information function is easy to fall into local optimalization,and the precision of registration result is improved obviously.

Key words: Image registration,Mutual information,Firefly algorithm