US Patent 7787934 Fiducial marker devices, tools, and methods

This document discusses, among other things, a fiducial marker assembly that includes an internally engagable base. The base is sized and shaped to be mounted flush to or recessed from an outer surface of a patient's skull, thereby reducing or avoiding patient discomfort. The fiducial marker assembly includes an imagable locator and a registration receptacle. A base insertion instrument is engaged to the base to attach the base to the patient's skull. In one example the base includes a faceted head, permitting a socket-like device to screw or unscrew the base into or out of the skull. In another example, the base includes at least one step or slot for engaging an insertion or extraction tool.