A frameless stereotaxic operating microscope for neurosurgery.

A new system, which we call the frameless stereotaxic operating microscope, is discussed. Its purpose is to display CT or other image data in the operating microscope in the correct scale, orientation, and position without the use of a stereotaxic frame. A nonimaging ultrasonic rangefinder allows the position of the operating microscope and the position of the patient to be determined. Discrete fiducial points on the patient's external anatomy are located in both image space and operating room space, linking the image data and the operating room. Physician-selected image information, e.g., tumor contours or guidance to predetermined targets, is projected through the optics of the operating microscope using a miniature cathode ray tube and a beam splitter. Projected images superpose the surgical field, reconstructed from image data to match the focal plane of the operating microscope. The algorithms on which the system is based are described, and the sources and effects of errors are discussed. The system's performance is simulated, providing an estimate of accuracy. Two phantoms are used to measure accuracy experimentally. Clinical results and observations are given.

A frameless stereotaxic integration of computerized tomographic imaging and the operating microscope.

A computer-based system has been developed for the integration and display of computerized tomography (CT) image data in the operating microscope in the correct perspective without requiring a stereotaxic frame. Spatial registration of the CT image data is accomplished by determination of the position of the operating microscope as its focal point is brought to each of three CT-imaged fiducial markers on the scalp. Monitoring of subsequent microscope positions allows appropriate reformatting of CT data into a common coordinate system. The position of the freely moveable microscope is determined by a non-imaging ultrasonic range-finder consisting of three spark gaps attached to the microscope and three microphones on a rigid support in the operating room. Measurement of the acoustic impulse transit times from the spark gaps to the microphones enables calculation of those distances and unique determination of the microscope position. The CT data are reformatted into a plane and orientation corresponding to the microscope's focal plane or to a deeper parallel plane if required. This reformatted information is then projected into the optics of the operating microscope using a miniature cathode ray tube and a beam splitter. The operating surgeon sees the CT information (such as a tumor boundary) superimposed upon the operating field in proper position, orientation, and scale.