A NONINVASIVE, REATTACHABLE SKULL FIDUCIAL MARKER SYSTEM - TECHNICAL NOTE

As computer-interactive technologies become more widely used in neuros urgery, radiology, and radiation therapy, the need for an optimum skul l fiducial marker system increases. In the past, intracranial localiza tion methods required precisely machined metal frames and rigid pin fi xation to the skull. Recently, this function has been performed using ''frameless'' computer-based systems that calculate brain position rel ative to a series of external reference points, the most accurate of w hich are screwed directly into the skull. A penetrating fiducial marke r system, however, is not well suited for applications requiring multi ple volume registrations over an extended time period. We describe a n ew skull fiducial marker system that attaches to the maxillary teeth a nd can be used repeatedly on different occasions. A curved bar, known as a Banana Bar (BB) extends backward from a custom mouthpiece around the side of the patient's head; the bar contains sites of attachment f or screw-in radiographic fiducial markers. Repositioning accuracy was quantitated using a photographic technique. A BB prototype was constru cted and tested in three subjects. The BB weighs less than 100 g and c an be comfortably held in position for up to 30 minutes. It takes less than 1 minute to screw in the mouthpiece and only seconds to secure t he BB to the teeth. One hundred twenty photographic measurements were analyzed from 60 repositionings over a minimum 3-week period. Standard deviations for the measurement series ranged from 0.29 to 0.86 mm. Re sults suggest that the BB may be an inexpensive, efficient, and accura te method for providing the external reference points needed for a wid e range of emerging computer-interactive applications.