We could use the geometry of the patient's head as its own reference system. Computer reconstruction's of CT and MRI provide excellent surface detail which we could match to the patient's head in real world space. Computer software would then match the surfaces of the patient's head on the operating table with the surface of the patient's head extracted from CT and MRI imaging. Operating room workspace coordinates could then be assigned to imaging coordinates. Holographic Imaging One problem with computer displays in surgery is that we as surgeons are interested in a three dimensional object.
Contemporary computers have only a two dimensional display screens.
We can display shaded graphics images and stereoscopic pairs. It's not the same as seeing things in three dimensions as is the case with a true projection hologram. However, a new process allows the production of a projection hologram from CT and MRI slice data within about 20 minutes. Ultimately, the ideal solution would be real time holography. Computer generated holograms have been around since the late 1970's.