1. A non-invasive medical imaging system, comprising: an imaging scanner capable of generating an imaging signal from a subject under observation inside the imaging scanner; a signal processing system in communication with said imaging scanner, and a data storage unit in communication with said signal processing system, wherein said data storage unit is suitable for storing a first image corresponding to a tissue region of the subject, wherein said signal processing unit is capable of generating a second image encoding the tissue region of the subject by performing a reconstruction based on said imaging signal; said imaging signal acquired at a later time than the first image; wherein said signal processing system is constructed to receive the imaging signal from the imaging scanner and the first image from the data storage unit respectively, wherein said signal processing system is adapted to provide a registered first image by registering said first image to said second image via a transformation in a space of diffeomorphism, wherein said signal processing system is further adapted to compute a difference image between said second image and the registered first image; and wherein said signal processing system is further adapted to output said difference image.