I had one. The way it worked for me was they first put the stuff into my veins and then told me to come back in two hours. I was to drink at least a quart of water during that time and then you have to go to the bathroom right before they start scanning (or else your bladder glows like a light bulb). You just have to lay really still but of course, that is when you feel a tickle in the back of your throat. It's not enclosed or noisy like an MRI. They gave me a card certifying that I was radioactive from a test, in case I needed to get through airport security. ha, ha Was overall much easier than an MRI.