Image Mask to NURBS

I've got a 3D mask corresponding to an object in a volumetric image (e.g., a stack of CT slices). I would like to take this mask, and fit a NURBS surface to its border. In other words, I want to define the shape of the object with a NURBS surface. I have no past experience working with NURBS (I'm reading a bunch about them right now). Has anyone tackled this type of problem before?

Thanks in advance for any insights, Justin