To the best of my knowledge, the imaging presents no risk whatsoever. It's done with ultrasound technique, and if it's done by a well-trained technician the results are significantly better than if it's done by someone who hasn't been trained in Zamboni's actual technique.
We started doing them without being trained by Zamboni, and some people with MS had negative studies. We thought that not everybody with MS was going to have CCSVI. I don't know if everybody with MS has CCSVI or not, but when we restudied the patients we had initially done prior to our Zamboni training, they all came back with criteria that met Zamboni's diagnosis of CCSVI after we had been properly trained by Zamboni.