…and I’m a little bit nervous. I’ve never had one before. What are they like, does anyone know? I know you have to lie inside the machine (I’ve seen that much on TV), but I know nothing about what happens once you’re in there.
Redwolf
It’s not a big deal, really. If your hospital has one of those new “open
MRI machines”, then you don’t even have feel enclosed. The only
hard part is that you have to hold quite still for a while.
When I have mine a few years ago, they had me wear something
that resembled scrubs (not a hospital gown), because clothing
might have metal on it, and remove ALL jewelry. They gave me
headphones tuned to the radio station of my choice so I’d have
something to listen to (make sure you have them turn it up loud
enough that the machine noise doesn’t drown out the radio). Then,
they slid me into the tube. For the next 10 minutes, I just closed my
eyes and relaxed, and held very still (if you meditate, this would be
an excellent time). The tube around me made noises like someone
banging their fist on a table, but I could ignore it pretty easily by
listening to the radio. Then, they slid me out, I got dressed, and I left.
It was really not bad at all. If you are having some kind of full body
MRI, it might take a little longer, but shouldn’t be too long overall.
If you call ahead and check, you might be able to get them to put in
a CD that you brought (depending on their sound system). If so, I
think this would help. Bring a familiar and relaxing CD that will help
you stay calm and still. There’s nothing to be afraid of, but some
people do get nervous anyway.
Good luck, and I hope your results are satisfactory!
I’ve had several. They inject you with something that leaves a metallic taste in your mouth, and you do have to be very still. I kinda like the tube. I’ve fallen asleep in it twice. To be sure, it is loud, but I’ve fallen asleep during hurricanes, so I’m wierd that way. 
Blessings to you Redwolf. We’ll say a quick prayer for you.
LJ
I didn’t have an injection. I think that is a specific kind of test.
(edited to add: D’oh! Much of the information in my post was already given above, so this is skippable. Damn time-lag . . .)
I hope the scan shows everything’s okay.
Having an MRI scan doesn’t hurt at all. You’ll be asked to remove anything on your body made of metal (they use a very powerful magnet). Depending on what you’re being scanned for, you may have only a part of your body inserted in the cylinder. A full body scan can take some time (up to an hour) while scans of specific areas will take less time.
The scanning center you’re going to may have a new “open MRI”, which is less claustrophobic than the tube-type machines.
You’ll be asked to lie quietly and breathe gently for best results. There’ll be a relatively loud noise – somewhat like hammering – but you won’t feel anything. The magnetic field essentially causes your cells to vibrate imperceptively (to you) and emit electrical signals, that are recorded and interpreted by the machine.
Think of it as a relaxing lie-down (albeit with a neighbor building something in the unit next door). I trust you’ll be fine.
Its terrible. You can’t even smoke while you’re in there, and then for weeks afterwards your body will set off every grocery store price scanner and all the shoplifting detectors at the mall. 
djm
You’re thinking of a PET scan.
I had one of my head. It does not hurt or feel at all weird. The machine and surroundings were unfamiliar but there is truly nothing to feel nervous about. I had no injection. You have to be still, but just relax and think of it, like herbivore12 said, as a chance to take a nap. You’ll feel refreshed afterwards 
. Best wishes.
I had one just eight days ago! 
It wasn’t scarey at all (I’ve had so many different medical tests lately that they’re routine for me now), but while inside the machine, with my head held in place by pieces of foam through an umpire-mask thing (can’t move your head much or it’ll mess up the results), I heard a lot of loud pounding noises, as though five or six people were outside pounding on the machine. This is just the noise the machine makes, though so try not to think about it.
You just lay there for thirty minutes, and it’s over with, then you go home. They played the radio for me but the knocking/pounding sounds nearly drowned out the radio. I find that laying still like that reminds one of being in a coffin, and it’s a good time to meditate and pray, since you’re laying still anyway. But it’s actually impossible to take a nap because the knocking/pounding sounds are too bothersome, IMHO.
Oh, and they gave me a rubber ball to squeeze, and if I’d squozen it it would’ve sounded a bell and the nurses would let me out.
Well, it’s over! Thanks for the encouragement, folks
I’m very glad they only had to put me into that thing up to my chest. I’m moderately claustrophobic, and that space was really, really small! I would not have been able to stand it if I’d had to go in head-first. As it was, I kept asking the operator for assurance that I wasn’t sliding further in (thank God for patient technicians with pleasant, reassuring voices!). No radio, but they did give me some ear plugs, which were somewhat helpful. If I ever have to have a full-body scan, I’ll either need to have sedation or they’ll need to find me one of those more open ones.
The culprit is my left knee. A little over a month ago, it started to swell, more or less spontaneously (I was actually just sitting in the choir loft when it started. We’re refering to it as my “honorable choral injury” ), and for a while I couldn’t bend it at all. The swelling has gone down some, but it still feels tight, and I can’t kneel on it. The doc suspects a cartilage tear, so that’s what this was all about today. If this test is negative, the next step is blood work, and possibly taking a sample of the fluid around the knee joint, to see if there’s something else going on. If this test is positive, the likely next step will be arthroscopic surgery.
Redwolf
Well, glad you got through this okay. Hope they get it figured out soon. A bum knee is no fun!
Do a test. Turn the lights off and stand near a mirror. Are you glowing. 
djm
I had one MRI for my shoulder, which means that my head was deep into the tube. When I was in college I used to crawl through small spaces in caves, so feeling enclosed didn’t bother me.
What did bother me was the loud noise from the hum of the magnets. I have sensitive hearing, so even with the ear plugs and the headphones, I was very glad when it was over. Also, not having health insurance, I was bothered by the $1500 cost.
Oh, you are so bad! You’re wrong, too. Wrong, wrong, wrong!
You won’t GLOW from this, Red. But, do you have one of those old-fashioned microwave leak detectors? If you do, you’ll set it off.
Really.
when I first was hired, I did NMR analysis in the lab. It the same principal as an MRI - they decided that if they called the medical instrument a nuclear magnetic resonance instrument people would freak out, so they changed the name to magnetic resonance imaging.
We learned a lot about the big magnets. This was in 1978, and wind-up watches were still the norm. I STILL have a watch that had the mechanism frozen from working above the magnet. You also didn’t want to leave data tapes anywhere near it - and many of the first matrix badges were wiped clean by being near it.
It’s really a very simple concept. You surround something with radio frequency (in our case, we were exciting hydrogen atoms) and then the magnets draw these toward themselves. You get calculations or “maps” based on the relaxation rates of the atoms. While I’m not sure what frequecy the medical instruments are looking at, it’s probably the hydrogen atoms on the water molecules in the body.
So - as long as you don’t have an old watch on, and you didn’t take any casette tapes or credit cards in with you, you are fine!
As the result of a brain tumor I have to have an MRI on a regular basis. My head goes into the center of the machine. The worst problem I have had was having to redo a scan because I was snoring. I have a real hard time staying awake.
Ron
Man, I really never realized I was that claustrophobic, but there’s no way they’d get my head into that thing without filling me with enough Tullamore Dew (or Demerol!) to pickle me! I nearly freaked out with my head OUTSIDE the machine when I thought I was going all the way in.
I guess spelunking is not likely to be my game, eh?
Redwolf
With the imaging, they set up on a resonant frequency (default is hydrogen, but they can do other nuclei, too), then put an additional oscillation on the field at an acoustical frequency. This is in two dimensions, and each of these scans makes a slice. Then they do this for however many slices they need to make the 3-d map. This acoustic-frequency oscillation is what makes the things so damn loud.
I’ve had two, one knee and one shoulder. To me it sounded as though I was inside a speaker connected to an amplifier with a really bad ground loop – 60-cycle punctuated by big clunks.
“Open” is evidently a relative term. My face (even for the knee scan) was about two inches from the top face of the magnet pole in a place that was very proud of their “open” setup.
It really is a fascinating technology. I’ve seen the pictures they get, and they’re amazing. I’m kind of hoping I’ll get to see mine, even if there’s nothing the othopedic surgeon can do for the knee.
Redwolf
My sister got down in her back, a few years ago. She was bedfast, and in intense pain, for a month. The Indian Health System wouldn’t do anything, except give her medication, because the Indian Hospital didn’t have an MRI machine and we live in a county that was too poor to afford to send her for one by contract health (you have to go through your own county). And no doctor would treat her condition without an MRI.
Eventually she managed to get an MRI, by filing for workmen’s compensation, or something. It was a pretty long deal for her, and noisy.