since we are on the subject, i'm having an mri on my knee next week. the question i have is, how is this possible with all the metal in my leg?
Good question. It is possible, and we do it all the time.
There are many myths, and misconceptions about metal in MRI. The "medical metal" is always fine. Stuff like your's, implants, joint replacements, dental work, etc. Typically that stuff is titanium,(non ferro-magnetic) and while some stuff is stainless steel(ferris) it isn't a problem from a safety stand point.
Contrary to shows like House.
(I paid for that episode for about a month) The magnet isn't strong enough to pull metal out of a body.
The issue is if the metal is close to the area of anatomy we are attempting to image. Your metal is plenty far away from your knee. You pic.s will come out just fine. Even if we are looking at your ankle, we can still get some useful information, though a lot of the area will be obscured by the metal. Nothing we can do about it, can't take it out. Same as dental work.
The big things we worry about are loose non medical metal. Car keys, can fly through the air. Office chairs, like dystopia showed, etc.
The next is electronics. The magnet will kill them. Cell phones, and of course the biggie....pacemakers.
The last two are the most dangerous. In a magnetic field, the field itself has the ability to induce electric current. If that current finds it's way to a "circuit" i.e. pacemaker wires, it cna shock the heart into a bad rhythm. Again, bad.
Typically when the current finds a metal object, it is not in a circuit, and thus has resistance.
current+resistance = heat. very bad.
You however, are good to go. Good luck.
