Frameless to frame-based registration system

This invention involves apparatus and methods for relating image scan data of a patient's anatomy from an imaging scanner to a device attached to said patient's anatomy or to an apparatus located nearby said patient's anatomy. In one embodiment it includes identification of fiducial points or markers on or near the patient's anatomy in the image scan data, and subsequently relating these fiducial points to reference points or structures connected to an apparatus attached to or nearby the patient's body. Such an apparatus might be a surgical head clamp or stereotactic frame or arc which has been attached to the patient's head at the time of surgery. A mapping is made between the coordinate frame data of the scan image to the coordinate reference frame of the patient attachment means or external apparatus by physically referencing the fiducial points to the patient attachment means or external apparatus. In one embodiment, such registration can be in the form of distance or coordinate measurements between the fiducial points on the patient's body and the reference points on the external apparatus. Applications are given in the field of frameless stereotaxy, radiosurgery, and stereotactic frame application.