An image processing method for the 3D display of a patients organ in which a surgical instrument is positioned, using a medical imaging system comprising a rotating C-arm able to be positioned in at least two angular positions, the C-arm comprising a radiation source at one of its ends, a detector at the other of its ends arranged facing the radiation source, and a collimator arranged between the radiation source and the detector and defining an illumination zone, characterized in that the collimator is adjusted according to the angular position of the rotating C-arm to determine the illumination zone so that the radiation only passes through a region surrounding the surgical instrument.
