1. A medical image processing apparatus, comprising:— an image selection unit configured to obtain a series of sets of image data, each set of image data representative of a region at a different time, and automatically determine a sub-region of interest; and a registration unit configured to, for each of a plurality of sets of image data in the series, perform a registration, for the sub-region of interest, to register one of a reference data set of the series and the set of image data to the other of that reference data set and the set of image data.