A system for finding a 3D target without a 3D image

We present here a framework for a system that tracks one or more 3D anatomical targets without the need for a preoperative 3D image. Multiple 2D projection images are taken using a tracked, calibrated fluoroscope. The user manually locates each target on each of the fluoroscopic views. A least-squares minimization algorithm triangulates the best-fit position of each target in the 3D space of the tracking system: using the known projection matrices from 3D space into image space, we use matrix minimization to find the 3D position that projects closest to the located target positions in the 2D images. A tracked endoscope, whose projection geometry has been pre-calibrated, is then introduced to the operating field. Because the position of the targets in the tracking space is known, a rendering of the targets may be projected onto the endoscope view, thus allowing the endoscope to be easily brought into the target vicinity even when the endoscope field of view is blocked, e.g. by blood or tissue. An example application for such a device is trauma surgery, e.g., removal of a foreign object. Time, scheduling considerations and concern about excessive radiation exposure may prohibit the acquisition of a 3D image, such as a CT scan, which is required for traditional image guidance systems; it is however advantageous to have 3D information about the target locations available, which is not possible using fluoroscopic guidance alone.