图像配准中最有挑战的是图像包含不同的形态特征。这种情况下，直接比较灰度水平的方法是不可行的。交互信息的评估很好地克服了多模态配准的困难。-Some of the most challenging cases of image registration arise when images of different modal-ities are involved. In such cases, metrics based on direct comparison of gray level