A computer-assisted system (100) for guiding a surgical instrument (25) in the body of a patient wherein an electronic unit is configured to: import a plurality of two-dimensional images I1, I2, ... Ii,... In of an internal portion of the human body of the patient process the imported images in order to define a reconstructed three-dimensional image that represents an anatomical volume of interest perform scans of a portion of the patients body by means of a calibrator marker (24) compare one or more scans with the curves defined on the three-dimensional image to detect matches if a least one match is detected, the reference system of the reconstructed two-dimensional image is aligned with the reference system of a location sensor (20).
