A method, including, receiving three-dimensionaltomographic data with respect to a body of a livingsubject, and using the data to generate a representationof an external surface of the body and displaying therepresentation on a screen. The method further includesinserting an invasive instrument into a region of thebody and identifying a position of the instrument in thebody. The method also includes rendering an area of theexternal surface surrounding the identified position ofthe instrument locally transparent in the displayedrepresentation, so as to make visible on the screen aninternal structure of the body in a vicinity of theidentified position.
