Fluoroscope

Abstract: A system employs a tracker and a set of substantially non-shadowing point markers, arranged in a fixed pattern or set in a fluoroscope calibration fixture that is imaged in each shot. The fixture is preferably affixed to the image detector of the fluoroscope, and tracking elements secured with respect to the fixture and at least one of a tool and the patient, provide respective position data irrespective of movement. A marker detection module identifies markers imaged in each shot, and a processor applies the known marker positions to model the projection geometry, e.g., camera axis and focus, for the shot and, together with the tracked tool position, form a corrected tool navigation image. In one embodiment an inverting distortion correction converts the tracked or actual location of the tool and displays the tool on the fluoroscopic image to guide the surgeon in tool navigation. In another aspect of the invention, the fluoroscope takes a series of frames while rotating in a plane about the patient, and the camera models derived from the marker images in each frame are applied to define a common center and coordinate axes in the imaged tissue region to which all of the fluoroscope view may be registered. The processor then filters and back-projects the image data or otherwise forms a volume image data set corresponding to the region of tissue being imaged, and desired fluoro-CT planar images of a the imaged patient volume are constructed from this data set. Planes may then be constructed and displayed without requiring complex tracking and image correlation systems previously needed for operating-room management of MRI, CT or PET study image data. Further, the fluoro-CT images thus constructed may be directly registered to preoperative MRI, CT or PET 3D image data, or may obviate the need for such preoperative imaging. Preferably, the tracker employs electromagnetic tracking elements, as shown for example in U.S. Pat. No. 5,967,980, to generate and/or detect electromagnetic field components unobstructed by the patient and intervening structures, and to determine coordinates directly referenced to the patient, the tool or the camera. The calibration fixture may be implemented with BBs in a radiolucent block of structural foam, and/or may be implemented by microlithographic techniques, in which case magnetic tracking elements may be simultaneously formed in registry with the markers on a sheet that mounts to the camera, is incorporated in a radiographic support table, or otherwise positioned to be imaged in each shot.