In vivo accuracy testing and clinical experience with the ISG Viewing Wand.

OBJECTIVE: A frameless stereotactic system (the Viewing Wand; Elekta Instruments, Atlanta, GA) has been developed for use with preoperative computed tomography, magnetic resonance imaging, and positron emission tomography as an adjunct for surgical planning and intraoperative navigation. This clinical study was designed to evaluate the safety, efficacy, and accuracy of the Viewing Wand in a variety of intracranial procedures. METHODS: We used this system in 250 patients undergoing a wide range of neurosurgical procedures from July 1990 to July 1994, to assess its clinical usefulness and safety. In a subset of 45 neurosurgical patients studied between March 1993 and March 1994, a battery of objective accuracy measurements was obtained before and during surgery. RESULTS: In this series, there were no instances of adverse outcomes attributable to the use of this system. A comparison of two alternative patient-image registration techniques established that the fiducial-fit method was slightly more accurate than the surface-fit method (geometric means = 2.51 and 3.03 mm, respectively). The clinical accuracy achieved with magnetic resonance imaging was nearly equivalent to that with computed tomography. CONCLUSIONS: On the basis of this clinical series, recommendations are made regarding preoperative scanning parameters, registration techniques, and methods for reestablishing registration if needed during the course of surgery. The primary clinical benefits of the wand in this series were improved intraoperative navigation and surgical safety. For most cases, the wand was also useful in planning the location and size of the scalp incision, craniotomy, or corticotomy, as well as the extent of surgical resection.

Frameless stereotaxic integration of CT imaging data: accuracy and initial applications.

To evaluate the spatial accuracy of a rapid interactive method of transferring computed tomographic (CT) information between its display on a computer screen to its source (test object, operating field), a multidimensional computer combined with a six-jointed position-sensing mechanical arm was tested with a Plexiglas model consisting of 50 rods of varied height and known location, a plastic replica of the skull, and, subsequently, three patients. The median error value between image and real location was 1-2 mm (P > .95), regardless of the registration target sites. The accuracy, however, increased with the selection of widespread registration points, and 95% of all errors were below 3.70 mm (P > .95). The results compare favorably with the four most commonly used stereotaxic framed units. A misregistration error of 0.3-2.2 mm was found during intraoperative correlation between anatomy on the CT display and actual anatomic location in the operative field.