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MRI helps surgical planing November 18, 2007

Posted by tomography in development, MRI, Surgery.
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The preoperative magnetic resonance imaging (MRI) image is no longer accurate enough for brain surgery.

brainsurgeryMRI

Everything changes after the surgeons open your skull. Your brain, and the tumor inside it, no longer fully float in their protective bath of cerebrospinal fluid. Gravity comes into play, as does the atmospheric pressure of the operating theater. The brain responds to these foreign forces, the cerebral tissue sagging, rebounding and changing shape. The tumor that the neurosurgeons want to remove also has changed position.

Thus, the brain the surgeon operates on is a different shape from the one depicted in the preoperative MRI. Of course, once the surgeon begins work, the shape of the brain changes even more. The brain’s changing shape is a problem not only of space, but of time.

In essence, the William and Mary team provides the surgical team with a dynamic computer model of the patient’s brain. In clinical trials, Chrisochoides (mathematician professor at the College of William and Mary) says his team can render a new model in six or seven minutes, but hopes to be able to do so in under two minutes.

We want to help the neurosurgeon make an informed decision of what to cut, where the critical paths are, what areas to avoid, he said. I’m neither a neurosurgeon nor a doctor, so the contribution of my research is to make this distillation of objects really, really, really fast.

The process begins with the acquisition of a variety of images before the surgery – images which are otherwise unavailable in the middle of the procedure. Low-resolution intraoperative data allows the tracking of the shift of brain matter and calculates how to change the preoperative images accordingly.

The brain, of course, is an elastic object.

If you push it, -Chrisochoides said-, it takes energy and then after a while it settles down. We can calculate the place where it settles by solving the partial differential equation. Mathematicians can tell us that there is a solution, but they cannot tell us what the solution is. There’s no such thing for this equation. There’s no analytic solution. So we have to approximate.

Chrisochoides approximates the geometry of the patient’s brain by tessellating it into triangles in three dimensions, or in other words, generating a mesh representing the brain. Users wear 3D glasses to examine projected images of a brain. The glasses give the audience a striking 3D effect, showing off the curves of the vector arrows indicating how displacement was acting on the brain.

Source: NSF

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