FRAMELESS STEREOTAXY WITH REAL-TIME TRACKING OF PATIENT HEAD MOVEMENTAND RETROSPECTIVE PATIENT-IMAGE REGISTRATION

The accuracy of a novel frameless stereotactic system was determined d uring 10 surgeries performed to resect brain tumors. An array of three charge-coupled device cameras tracked the locations of infrared light -emitting diodes on a hand-held stylus and on a reference frame attach ed to the patient's skull with a single bone screw. Patient-image regi stration was achieved retrospectively by digitizing randomly chosen sc alp points with the system and fitting them to a scalp surface model d erived from magnetic resonance (MR) images. The reference frame enable d continual correction for patient head movements so that registration was maintained even when the patient's head was not immobilized in a surgical clamp. The location of the stylus was displayed in real-time on cross-sectional and three-dimensional MR images of the head; this i nformation was used to predict the locations of small intracranial les ions. The average distance (and standard deviation) between the actual position of the mass and its stereotactically predicted location was 4.8 +/- 3.5 mm. The authors conclude that frameless stereotaxy can be used for accurate localization of intracranial masses without resortin g to using fiducial markers during presurgical imaging and without imm obilizing the patient's head during surgery.