1. An imaging method for the monitoring of an anatomical region during insertion of a metallic object inside the region, the method comprising: a) acquiring a three-dimensional image of a specific anatomical district of the body under examination by a computed axial tomography device and storing said three-dimensional image; b) finding three non-linearly aligned anatomical reference points within said anatomical district; c) acquiring a two-dimensional image along a first section slice of said anatomical district containing said three anatomical reference points by an ultrasound probe; d) correlating said three anatomical reference points of said two-dimensional image with said three-dimensional image and identifying said first section slice of the acquired two-dimensional image within the stored three-dimensional image; e) constructing a first two-dimensional image with data of the three-dimensional image falling along said first section slice and corresponding to that of the acquired two-dimensional image; f) moving said ultrasound probe towards a further section slice of said anatomical district having a position and/or orientation different than that of said first section slice; g) tracking the displacement of said ultrasound probe for obtaining the image at said further section slice; h) identifying said further section slice within the stored three-dimensional image by using data related to the tracking of the displacement of said ultrasound probe; i) constructing a second two-dimensional image with data of the three-dimensional image falling along said further section slice identified at step h); j) displaying the two-dimensional image obtained at step i) and keeping in place said ultrasound probe; k) introducing a metallic object; l) acquiring one or more further two-dimensional image along said further section slice, said image being acquired and generated in real time; and m) combining the second two-dimensional image which has been constructed from the three-dimensional data and the further two-dimensional images, and displaying the combination image, wherein the contribution of the first and second two-dimensional images reconstructed from the three-dimensional data corresponds to the representation of an anatomical structure and the contribution of the image corresponds to the representation of the metallic object.