A method is provided comprising: obtaining first and second datasets representative of first and second images of an object at different times, respectively； obtaining a deformation field, representative of changes between the first and second data sets, by performing a rigid or non-rigid registration； generating one or more masks and/or segmentations for selecting elements of the first image； selecting elements of the first image； transforming the first dataset using the deformation field to project the selected elements onto the second image； visualizing the deformation field or previously specified portions thereof； processing the deformation field or previously specified portions thereof to obtain data representative of different predetermined types of deformation； and visualizing the deformation field or one or more selected portions thereof, thereby to visualize the predetermined types of deformations separately and to enable a differentiation between changes in the patient and changes, in particular errors in the patient's position.
