A system for planning a percutaneous procedure provides a patient 3-dimensional image data set within which an instrument trajectory is defined, for example, by selecting a skin entry point and a target point. A line, or “planned path,” is generated between the points. The system determines whether the path can be targeted so an optical axis of a movable arm coincides with the path so that a laser can be used for instrument guidance or whether a planned path can be targeted so that a C-arm can be made to coincide with the path so that the extension of the path is projected onto a radiation detector, using x-ray radiation. If neither laser guidance or x-ray guidance can be used, the path is replanned.