THE APPLICATION ACCURACY OF STEREOTAXIC FRAMES

THE PURPOSE OF incorporating stereotactic methodology into neurosurgic al operations is to achieve a consistently high degree of accuracy in localizing intracranial targets. Therefore, the limits of resolution f or the operation are a function of the accuracy of the particular ster eotactic frame system. The total clinically relevant error (applicatio n accuracy) comprises errors associated with each procedural step, inc luding imaging, target selection, vector calculations, and the mechani cal errors of stereotactic frames. To evaluate these parameters, a sys tematic error analysis was carried out with four commonly used stereot actic devices: the Brown-Roberts-Wells, the Cosman-Roberts-Wells, the Kelly-Goerss COMPASS (modified Todd-Wells), and the Leksell frames. Ov er 21,500 independent accuracy test measurements were made with 11,000 computed tomograms. The results suggest a potentially significant deg ree of error in the application accuracy of all stereotactic instrumen ts, which is accentuated by but not entirely due to imaging-associated errors. Clinically encountered levels of weightbearing by stereotacti c frames may have a pronounced effect on their mechanical accuracy. Bo th the reapplication of aiming are assemblies and the use of phantom b ase units introduce independent sources of mechanical inaccuracy into stereotactic procedures. The scope of individual error values and thei r determining factors must be considered with every clinical use of st ereotactic frame systems.