and either tracks the markers or bodies manually or the software can automatically track them. However, biplanar analysis requires that all tracking be done on both video frames at the same time, positioning the object in free space. Both X-ray cameras have to be calibrated using an object of known volume. This allows the software to locate the cameras' positions relative to each other and then allows the user to position the 3-D model of the object in line with both video frames. The tracking data is generated for each marker or body and then applied to the local anatomical bodies. The tracking data is then further defined as anatomical terms of motion in free space. Applications X-ray motion analysis can be used in human gait analysis to measure the kinematics of the lower limbs. Treadmill gait or overground gait can be measured depending on the mobility of the X-ray system. Other types of movements, such as a jump-cut maneuver, have also been recorded. By combining X-ray motion analysis with force platforms, a joint torque analysis can be performed. Rehabilitation is an important application of X-ray motion analysis. X-ray imaging has been used for medical diagnostic purposes since shortly after its discovery in 1895. X-ray motion analysis can be utilized in joint imaging or analyzing joint-related diseases. It has been used to quantify osteoarthritis in the knee, estimate knee cartilage contact areas, and analyze the results of rotator cuff repair by imaging the shoulder joint, among other applications. Animal locomotion can also be analyzed with X-ray imaging. As long as the animal can be placed between the X-ray emitter and the camera, the subject can be imaged. Examples of gaits that have been studied are rats, guineafowl, horses, bipedal birds, and frogs, among others. Aside from locomotion, X-ray motion analysis has been utilized in the study and research of other moving morphology analyses, such as pig mastication and movement of the temporomandibular joint in rabbits. See also Video motion analysis Roentgen Stereophotogrammetric Analysis Radiography Fluoroscopy References X-rays Fluoroscopy Film and video technology Radiography Motion in computer vision