Down to the Bone

Night and Day: CTX of this flying pigeon (bottom) yields more detail than an x-ray can (top). Stephen Gatesy

For most of us, the phrase "super x-ray vision" conjures a pair of spiral-print cardboard spectacles ordered from the back of a cereal box. But now an imaging system developed at Brown University delivers the real thing, combining computed-tomography (CT) scanners, x-ray video and computer software to give doctors and researchers a three-dimensional look at bones in motion.

Although several medical-imaging technologies already exist for peering into living things, each one compromises either speed, resolution or depth. CT scans, for instance, offer detailed 3-D views, but scanning is slow and requires the subject to stay completely motionless. A technique called fluoroscopy can create video by taking multiple x-rays in rapid succession, but it's limited to producing two-dimensional images and has much lower resolution than CT.

The new process, known as CTX imaging, combines both of these technologies to produce 3-D animations of bones in motion-walking, running, jumping. Though still in prototype form, the room-size system is already helping researchers to answer tough questions about animal biomechanics, such as how flight evolved in birds. It could also be a valuable tool for orthopedic surgeons, who might use it to plan better treatments for bone-, ligament- and joint-related injuries.

Elizabeth Brainerd, the biomechanics professor at Brown leading the CTX program, says that although the technology won't fit into a pair of glasses anytime soon, a commercial version of the system that produces real-time video should be ready by 2010.

How it Works
CTX imaging combines CT scans with x-ray video to produce 3-D animations. The process starts with a traditional CT scan of a subject-say, an alligator-to create a 3-D model of its bone structure. Then high-speed fluoroscopy records the gator in motion from two different angles. Researchers feed these two data sets into image-processing software, which merges them to produce an animation of bones in action from any angle. The 3-D view has resolution down to a tenth of a millimeter and captures motion at 1,000 frames per second.