XROMM Day 2: This little piggy bites … in 3-D

Again, if you missed previous posts on XROMM, please read those first for better context of the discussion that follows: see what XROMM is all about, why I’m excited to be learning it, and what I’ve already done.

On our second day in the course, we took the next step to synch two different, simultaneous X-ray movies of a mini-pig eating with a three-dimensional model of its skull in the MAYA program.  These X-ray films were taken on the C-arm x-ray machines I mentioned in my previous post by Dr. Beth Brainerd and colleagues, and we were essentially learning by replicating their process.

Dr. B. and the Mini-Pig

Me and mini-pig’s skull. The original movie was filmed back in 2006, so the mini-pig that stars in the X-rays has since passed on to piggy heaven. Here I am holding the actual skull of the animal that you will see in the animation.

In XROMM, you essentially have a work-flow like this:

  1. Film an animal behavior from two directions using calibrated X-ray cameras.  The animal usually has tiny, spherical beads implanted surgically into a few of the bones of interest prior to the filming.  As an important note here, all such films and surgeries are done under strict animal welfare protocols and the animals are not harmed: the X-ray dosages are as low or lower than that of humans exposed to x-rays for diagnosis, and the beads are tiny and biologically inert.
  2. After filming the animal’s behavior, the skeleton’s three-dimensional geometry is often CT-scanned from the animal.
  3. The CT-scan bone data are converted into geometrically-accurate 3-D representations of the bones of interest.
  4. In MAYA and MATLAB, the films from the two x-ray cameras are virtually “projected,” and the beads implanted into the animal subject show up as little dots.  These dots show up as little spheres in the CT-scanned bones you import into the MAYA program.
  5. Things then get more technical, but suffice it to say that the beads you see in the X-ray films and the spheres in the CT bones are synched.  The movements of the beads (spheres) are digitized in three-dimensions calibrated from the two camera views, and then the virtual bones are “cemented” to these spheres.  Then, as the spheres move, the bones follow, and what you get is a three-dimensional reconstruction of the 2-D x-ray films!

Here is a screen shot of the animation made in XROMM today.

Mini-Pig X-ray and Reconstruction

What you get from XROMM: to the left is one of the two X-ray films, and to the right is the 3-D skull reconstruction of the mini-pig.

Here is an animation of what you get — I still can’t believe we can do this!

Dr. B. Contemplates the Mini-Pig

Dr. B. Contemplates the mini-pig skull.

And we’re not even done yet.  Stay tuned …


One thought on “XROMM Day 2: This little piggy bites … in 3-D

  1. Pingback: XROMM Days 3-5: Data, data, data | The Evolving Paleontologist

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