A technique for anatomic feature extraction and tracking on sequential digital X-ray images

The Craniofacial Research Instrumentation Laboratory at the University of California, San Francisco, has been developing systems for the acquisition and display of biostereometric data. Stereo photographs and X-ray images of the head are used to analyze growth and treatment effects during orthodontic treatment and orthognathic surgery. Recent efforts have been directed towards automating anatomic feature location and tracking on series of time-separated cranial X-rays.

Two tests were performed to evaluate the potential accuracies that could be achieved in feature tracking. In both tests, a series of cranial X-rays was converted to digital images using an array camera [Charge Injection Device (CID)] connected to a real-time video digitizer module or “frame grabber” installed in a microcomputer. The first test series consisted of a single X-ray image which was translated and rotated three times. The second series of images consisted of three actual cranial X-rays of a single subject, acquired over a period of approximately two years.

A number of anatomic features were manually selected on the first image of each series. The features were automatically tracked on subsequent digital images, and their locations compared to those derived from manual digitizing of the original film images.