Clinical evaluation of multimodality registration in frameless stereotaxy

Computer-assisted frameless neurosurgery bases its accuracy and reliability on registration. The aim of this prospective study was to compare the clinical accuracy of different registration techniques used for computer-assisted frameless neurosurgery. Ninety-eight registrations in 44 patients were used to compare the clinical accuracy of self-adhesive marker (MR) and facial landmark (FR) registrations used alone or in conjunction with surface-fit registration (MR/SR and FR/SR, respectively) for cranial neurosurgery. The computer estimated error (CEE) of each registration was compared to the real error (RE). This was obtained by holding the frameless pointer at the center of three different markers and measuring the distance from the real-time representation on the computer three-planar images to the center of the marker on the screen. The most accurate registration was obtained using MR; the RE of MR was 1.6 +/- 0.1 mm compared to 3.4 +/- 0.4 mm for FR. Although the smallest CEE error was obtained using MR/SR, this was not sustained by the RE. Furthermore, the RE of FR/SR was significantly larger than the CEE (Student t test, p <.001). This study corroborates previous results showing that, in the clinical setting, self-adhesive marker registration is more accurate than facial landmark registration. Furthermore, although surface-fit registration can be used in conjunction with self-adhesive marker registration, this does not improve the degree of real accuracy for cranial registration.