1. A method of analysing a medical scan image, the method comprising: defining an extent of a first region of interest in a first scan image; identifying a second region in a second scan image, the second region in the second scan image corresponding to the first region of interest in the first scan image; classifying each spatial location of the second region, to provide a classification of the spatial locations of the second region into at least one category of tissue type; and providing information about a proportion of the spatial location in the second region that correspond to the at least one category of tissue type.