Catching Evolution on the Run

3-D x-ray videos of species in motion will help scientists understand how they evolved.

Scientists at Brown University are developing an imaging technology that would capture the movement of bones and muscles of animals in high-speed 3-D videos. The technology, which has been developed previously in orthopedics to study joints in humans, will be used to study the evolution of movement and anatomy in species of fish, mammals, and birds to shed light on, for example, how birds developed flight. It could also help researchers better understand movement disorders in humans.

This image of a pigeon in flight shows what Brown researchers hope to accomplish with high-speed, 3-D x-ray video. In this case, a 3-D digital model of the pigeon's skeleton is matched by hand to an x-ray video sequence. The new technology will do the task automatically and with better accuracy. Credit: Brown University

Multimedia •  Watch a 3-D x-ray video of a pig in motion.

The lack of good imaging systems has been a major obstacle for people studying movement, says Rebecca German, a biologist at Johns Hopkins School of Medicine. "When you study any kind of movement, it happens in three dimensions," she says. "When you're limited to looking at it in two dimensions, you're only getting part of the story."

Scientists have previously developed high-speed, 3-D, x-ray video systems to study the human knee and other joints, particularly after injuries or surgery. But these technologies have been used only in a limited number of clinics for specific medical applications. The Brown team, led by biologist Elizabeth Brainerd, plans to develop a similar technology for evolutionary biologists that is flexible enough to analyze different animals as they walk, swim, fly, or jump.

The approach combines two imaging technologies: computed tomography, or CT, which uses a series of x-rays taken at different orientations to reconstruct a 3-D image of the bone and tissue inside the body; and x-ray video, or cinefluouroscopy, which is able to capture events as they happen in real time, but only in two dimensions. CT is used routinely in research and in medical practice, but it is a time-intensive process and produces only static images. X-ray video is frequently used by scientists studying movement.

To image a movement such as a pig walking, the researchers first create a 3-D model of the animal's anatomy using CT. Then they use two separate x-ray cameras to image the pig in motion from different angles. A computer matches the information from the CT model to the information in the 2-D videos to reconstruct a moving image in three dimensions. The Brown biologists have experimented with putting the two technologies together manually. Now, working with computer scientists, bioengineers, and orthopedic experts, they plan to create software to automatically align the data faster and with better accuracy to produce videos with a speed of up to 1,000 frames per second. The biologists hope to have a product that can be widely distributed to other scientists in about three years. According to German, such a technology will be a major leap forward for scientists investigating movement and "will open up whole new areas of research."