A COMPUTER-ASSISTED SYSTEM FOR 3-D FRAMELESS LOCALIZATION IN STEREOTAXIC MRI

A new low-cost PC-based system for 3-D localization of brain targets in stereotaxic imaging is presented. It relies on a method, using MR images, in which four markers are inserted in the fastenings of a Talairach stereotaxic frame during MRI examination. By locating these markers on the images with this system, the transformation matrixes can be computed to obtain the 3-D coordinates of the center of a tumour in the stereotaxic space or in the MRI space. The system calculates the frame and arc setting parameters of a probe trajectory to the target, either for an orthogonal or a double oblique approach if needed. Simulated probe trajectory intersections with the consecutive slices can be viewed in order to validate the trajectory before and during the surgical procedure. The method presents no major constraints in routine examinations. Up to the present time, 24 patients have undergone surgery assisted by this system. Mathematical details on calculation of the transformation matrixes are also given.