A medical imaging data processing apparatus comprises a receiving unit configured to receive first medical imaging data that represents a region of a subject at a first time, and second medical imaging data that represents the region of the subject at a second, later time, a registration unit configured to perform a registration procedure to obtain registration data representative of a registration between the first medical imaging data and the second medical imaging data, an evaluation unit configured to process the registration data to determine, for each of a plurality of positions in the region, a value of a registration measure, the registration measure representing at least one feature of the registration as a function of position, wherein the evaluation unit is configured to, for at least some of the plurality of positions in the region, determine whether an abnormality is present by comparing the value of the registration measure to a statistical atlas.