Computer-assisted guidance of a surgical instrument during diagnostic or therapeutic operations

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 patient's 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).