Stereotaxic localization of intracranial targets

We report on a useful clinical method for precisely locating intracranial targets. Utilizing the BRW system, the technique is currently used in stereotaxic irradiation of arteriovenous malformations. An intracranial localizer box, with four radio-opaque markers on each face, surrounds the patient's head and is attached to the BRW Head Ring. Two localization films are required. One film includes the target and the eight anterior and posterior markers, whereas the other film includes the target and the eight right and left markers. There are no constraints that the films be orthogonal or parallel to the box faces, only that the target and radio-opaque markers appear on the films. In addition, knowledge of the source-image and source-target distances are not required. Analysis of the projected target and radio-opaque markers gives both the target location and magnification. Simulation with the BRW Phantom Base demonstrates that point targets can be located with respect to the BRW system to within 0.3 mm and magnification determined to within 0.5%.