[Noah930]

There are different types of MRI machines. If they asked you that question, I'm guessing you're going for one of the traditional (non-"open") scanners.

It's like a long metal/plastic tube, that's just wider than your body. Fat people sometimes can't fit in. You'll lay down on a gantry, which will then slide into the tube. The tube will literally be justa couple inches from your face, which is why they ask if you're claustrophobic. Depending on what's being scanned, and if there are any technical difficulties (i.e. you move, thereby screwing up the scan), you might be in the tube for 20-45 minutes. It's pretty loud while the machine's running, too, so they'll give you a pair of earplugs. For technical interest, often times pieces of radiographic equipment (like the headrest in a CT/MRI machine) will be made of carbon fiber. Kinda neat to see industrial use of that stuff.

They'll ask you about the metal part, too. No shoes, watches, jewelry, belts, credit cards, etc, as the scanner is a big magnet. If you wear a watch into the room, you'll notice it stopping/running erratically. If you wear shoes into the tube (even while it's not actively scanning), you'll feel a gentle tug on them if you're inside the tube (i.e. from the metal nails or grommets). That tattoo bit was busted on MythBusters. The metal part is no joke, either. Every so often, you hear of a story where an oxygen tank was left inside the MRI room while a scan was being done. The tank winds up being some sort of magnetically-propelled projectile which winds up crushing the patient's skull, or causing some other grisly and preventable form of injury. Not meant to scare you--just meant to let you know that when the MRI tech asks you that question, it's a bit different than when the TSA guy asks you the same thing.