In the old days, if you wanted to look inside someones body, you had to cut them open. Less than ideal. Then came the miraculous X-ray machine, which peered inside the human form, no scalpels required. Nowadays, X-rays can even show your insides moving in unprecedented detail, allowing doctors to watch the flow of blood through the heart.
But X-rays have a shortcoming: They can only create images in two dimensions. CT scans, however, image bone in highly detailed 3-D. So what if you combined the two techniques, layering a 3-D CT scan over a 2-D X-ray movie? Well, youd get something called XROMM, or X-ray Reconstruction of Moving Morphology—technology thats giving researchers a stunning look at bones in motion. And if a recent paper on the open-source software behind XROMM is any indication, the technique is poised to transform the field of biomechanics.
That has big implications not just for human medicine, but for sciences understanding of animal anatomy. It lets us understand, for example, the details of how the ends of bones—where they interact at joints—how the shape of that relates to the way that the bones actually move, says Brown University biologist Beth Brainerd.
Say youve got a guinea fowl—kind of a chicken-like bird—and you want to see how its legs actually work. How the bones move, how they fit together, how joints bend. First you implant tiny metal pins in the leg bones, and then give the bird a good CT scan. Next you take X-ray video of it running around an arena. And the computer does the rest: The aforementioned open-source software works with the animation program Maya to layer the CT scan of the bones on top of the X-ray movie, using the metal pins as reference points.
What you end up with is an entrancing video of the guinea fowls leg bones in motion. It’s always this weird disembodied bird, just a pelvis and legs, says Browns Stephen Gatesy, who dreamed up the technique. It looks like something from RoboCop.
The technology can give researchers a better look at how bones move, and even how feet interact with the ground. Gatesy also has the guinea fowl traipse through radiolucent poppy seeds—which are less visible in X-rays than something like sand, so they don’t obscure the bone—to produce footprints. Those tracks can vary greatly depending on the viscosity of the material an animal is treading on. “We’re trying to kind of overturn this idea that tracks always look like feet,” Gatesy says. “And so the motion becomes critical for that.”
Tracking the guinea fowl’s movement could be big for paleontology, of all things. Birds are, after all, descended from dinosaurs, and dinosaurs left a lot of tracks behind. But depending on the consistency of mud, the footprints of a single species can vary widely. Theoretically, experiments with guinea fowl could shed light on how dinosaurs’ feet shifted as they sunk into the muck. The work could also hint at how dinosaurs got around. Keep in mind that paleontologists only have dino bones to work with—no tendons or muscles. If we can understand much better how the shapes of bones relate to motion, we can come up with more rigorous interpretations of how dinosaurs might have moved, says Brainerd.
Beyond birds and dinosaurs, the technology has also peered through a turtles shell. (The reptile swings its hips when it walks, in case you were wondering.) And its helping model the majesty that is the vacuum-face-feeding technique of fishes. (Many fishes hunt by rapidly opening their maws, creating a vacuum that sucks prey in.)
As for humans, the technique could help determine why, for example, women suffer more ACL injuries than men. (When it comes to people, researchers aren’t implanting pins in bones, of course. In this case, technicians manually join the CT scans and X-ray movies.) And perhaps more pressingly, it might be of use for amputees who endure uncomfortable prostheses. One of the things that some of our collaborates at the VA hospital in Providence are doing is looking at how the residual limb moves inside a prosthesis to try to improve the interface, says Brainerd.
With the melding of CT scans and X-rays, researchers are finally bringing a hint of Superman to science. Now if we could only get some invulnerability and laser eyes…