1. A method of registering volumetric scan data of a patient surgical site with actual patient position, comprising (a) obtaining, at a scan station, volumetric scan data of a surgical site of a patient, including data relating to plural selected features in the region, and storing the scan data in digital form in a scan-data file, (b) after moving the patient from the scan station to a surgical station, positioning an x-ray source and a detector screen for imaging at least a portion of said target region fluoroscopically at a selected orientation, (c) determining the coordinates of said x-ray source and detector at said positions in a fixed coordinate system, (d) activating the x-ray source to produce a fluoroscopic image of the patient region on said detector, (e) determining the image coordinates of said selected features in the target region in said fluoroscopic image in the fixed coordinate system, (f) using the coordinates determined in (c) and (e) to determine the actual coordinates of the selected features in said fixed coordinate system, and (f) matching the coordinates determined in (f) with those of the same features in the scan data, to place the scan data in the frame of reference of the patient.