TARGET POINT CALCULATION IN THE COMPUTERIZED-TOMOGRAPHY - COMPARISON OF DIFFERENT STEREOTAXIC METHODS

The adaptation of computerized tomography for stereotactic operations requires the transformation of the coordinates of the target point fro m the CT image space into the stereotactic frame space. Two basic solu tions for this transformation are realized in the most of the contempo rary stereotactical systems. The indirect geometric method adjusts the frame coordinate system mechanically and identifies its origin in the CT image. There are 6 degrees of freedom: 3 of rotation and 3 of tran slation which have to be taken into consideration. The second method i s a based on direct algebraic coordinate transformation and is indepen dent of the explicite knowledge of the relationship between the image and the frame space. A localization frame serves to determine a transf ormation matrix which, applied to any point in the image, transforms t he coordinates directly into the frame coordinate system. Only the alg ebraic method is independent of the position of the patient in the gan try. All other methods require high mechanical precision of the aligna ment and stability for the CT table.