Interactive sonar-operated device for stereotactic and open surgery.

An accuracy of +/- 1 mm in surgical localization of brain targets was reliably attained with a new sonar-operated system, provided that air turbulence was minimized. Since a conventional frame construction with coordinate settings has been disposed of, apart from a halo ring head holder, free access to the operating site is guaranteed. Using offset probes, measurements in depth can be realized with a relatively simple hardware arrangement. A small, 'floating' locator probe can be attached to all kinds of surgical instruments; its spatial position is computed in real time and immediately referred to computed tomography/magnetic resonance imaging scans. Although this work is still in progress, promising applications both in stereotactic and in open surgery are envisaged.