Camp. & Yuhr. with .4ppk. 7. pp. 8394511. IYX6 Pnnwd m Great Bntaul on86-95s3~ 86 s3.00+ .co Rrgamon Journals Lti zyxwvutsrqpon SYSTEM ANALYSIS OF STEREOTACTIC NEUROSURGERY BASED ON CT SCANS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ YUVAL LIROV Department of System Science and Mathematics. Washington University, St. Lo u is . MO 63130.U.S.A. MICHAEL W. VANNIER? Mallinckrodt Institute of Radiology. Washington University School of Medicine, St. Louis, MO 631 IO, U.S.A. (Received 15 November 1985) Communicated by E. Y. Rodin Abstract-Stereotaxic localization of target points identified on singleCT scanslicesobtained using commercially available frame systems is widely available. These systems have intrinsiclimitations imposed by the computational algorithms used to de termine the stereotaxic frame settings for a desired approach to the ta rget. Th e extant descriptions of stereotaxic frames a re mathematically incomplete, confounding efforts to de lineate the limitations of these devices andimprove their versatility. This re port provides a complece mathematical description for a commercially available device (Brown-Roberts-Wells stereotaxis system). This syste ms analysis was used to design and implement microcomputer-based (Apple Macintosh) interactive graphics software providing enhanced versatility in locating target points. selecting approach directions, a nd ha ndling sequences of framesettings needed in procedures wheremultiple interventions are required. Application of this new software in neurosurgical procedures to uniformly distribute interstitial radiotherapy sources through tumor masses is described. INTRODUCTION Intraoperative localization of intracranial abnormalities is an essential function for many neuro- surgical procedures. Historically,stereotaxic frames ha d be en designed a nd use d for intra- operative localization of spaceoccupying lesionsin brain surgery since 1905[1,2,7-10,13- 18,20,23,24,26-33,36-551. Stereotaxic localization systems designed be forethe mid-1970’s utilized conventional radiography with the patient’s head immobilized in a specially designed fixture. Intracranial landmarks we revisibleon the se radiographic systems only a fter intracranial introduction of air or contrast material. More recently, CT scanners were introduced, dramatically improving intracranial soft tissue contrast discrimination, so m anyabnormalities may be seen without intrathecal air or contrast material. The CT scanner is an idealdevice in manyways for stereotaxic localization. The geometrical accuracy of CT scanners is sufficient for most neurosurgical procedures. CT scans havehigh contrast and spatial uniformity in the plane of section, without geometric distortion due to m agnification found in conventional radiography. CT scanners produce images using d ig it a l computers, and a s a result, the images themselves havea digital format thatare stored in a general purpose minicomputer. Stereotaxic neurosurgical localization systems based on CT scanning for ta rget identification have been developed and several are commercially available[ 1,3-5,17,18,36,47-501. Th e re a re four problems that arise in stereotaxic neurosurgical applications. The first is target localization wherethe x, y locus of a specified point within a space occupying lesion found on a single CT scan slice m ustbe transformed into the three-dimensional coordinate system of the stereotaxic device. Second is the forward solutionfor a single probe to re ach the specified target by generating settings for the stereotaxic frame being used. Third is the forw ard solution for multiple probes, all of which must be mutually separated in space by a specified distance. Fourthis the requirement to a llow inde pendent specification of rhe probe entry point or direction from the surface of the skullto the desired target. :Address correspondence to: Michael W. Vannier, M.D., Mallinckrodt Institute of Radiology, 510 S. Kings Highway, St. Louis, MO 63110. 839