Frameless stereotaxy of the brain.

Today's neurosurgical journals are replete with advertisements for systems designed to provide image guidance during surgery. These so-called "frameless" stereotactic systems provide the surgeon with navigational information, relating the location of instruments in the operative field to preoperative imaging data. Such information minimizes invasiveness by more accurately selecting the best trajectory to the lesion, ensures more precise identification of normal structures, and guides complete removal of a lesion. To achieve these goals, all of these systems utilize the stereotactic principle of co-registration of the patient with an imaging study. This review will trace the development of image-guided surgery from its origins in frame-based stereotaxy to its current use as a surgical navigation methodology. A review of the more prevalent techniques and available systems will be presented, along with examples of specific applications of surgical navigation. Finally, some of the future directions of frameless stereotaxy will be discussed.