1. A computer implemented method for determining brain shift by analysing images of the brain, comprising the steps of: (i) taking a first image of the brain of a subject, the first image showing the position of blood vessels in the brain relative to a reference position, (ii) taking a second image of the brain that was acquired after an intervention on the subject, the second image having been acquired by Computed Tomography (CT) imaging apparatus and showing the position of blood vessels in the brain relative to the reference position, and (iii) calculating brain shift from a shift in position of the blood vessels in at least one region of interest of the brain, with respect to the reference position, between the first and second images and calculating a brain shift correction based on the calculated brain shift and updating the position targeted by a surgical robot based on the calculated brain shift correction.