MRI (More than Really Interesting)

Although many of my friends have left campus for the summer, I have remained to continue working in a lab on campus.  I've had the opportunity to learn much about different research techniques which I think will be of great use to my future.  But one of the most fascinating methods I've learned about recently is the ever-useful MRI.

For a few years I was addicted to this television series.

If you've ever seen a show like Gray's Anatomy or House, you've probably watched scenes where patients go into the donut scanner on a little cot and instantly the doctor starts looking at the images.  Well, obviously the tv shows are playing up the speed at which a scanner can actually operate.  But when you think about it, an MRI scanner is a seriously amazing piece of technology.

First of all, did you know that modern day scanners aren't hooked up to the power grid?  They are actually, to a degree, self-sustaining.  The magnet is essentially miles of wire all wrapped around a tube like a tesla coil.  And although I don't know the exact composition of the alloy used to make the wire, I do know that below 7 Kelvin, the wire has no resistance. And resistance is like friction, it'll eventually wear down a power source such as a battery, just as a ball will eventually quit rolling across the floor because of the friction.  But if you have no resistance, it means that you can keep the power cycling forever, just like a ball that would never stop rolling.

Of course, for all those chemistry geeks out there, they know 7 Kelvin is approximately -450 fahrenheit.  That's pretty damn cold.  So how did engineers deal with this problem?  Well, they built a vacuum.

Essentially, the coils of wire are kept in a bath of either liquid Helium or Nitrogen.  My university's new scanner (which is way cool!) uses liquid Helium to keep the coils at 3 Kelvin, plenty cold to keep resistance at zero.  And to keep the liquid helium from turning to gas, this whole apparatus is kept inside a vacuum.  Can you believe all this is necessary just to run a single MRI?

This also explains why the magnet is never turned off.  Because technically it's not hooked up to a power source (remember, once it's charged it never looses energy because the wire has no resistance), so there's nothing to unplug it from.  In an emergency, the only thing you can do is hit the emergency kill button.  This releases the liquid Helium (which turns to gas and pours out of the building through a specially designed system) and the wire regains resistance so the stored energy in the system dissipates.

However, this method is only to be used in life-threatening emergencies.  Killing the magnet like this can do untold amounts of damage.  First of all, thousands of liters are needed to keep the coils cold enough and Helium is becoming more pricey every day. Last I checked, I believe it priced somewhere around 9 dollars a liter.  Next, the sudden heating of the coils after the loss of liquid Helium can heat them so badly that they melt, meaning you have to replace the entire spool of miles of wire.  And of course, there's always the possibility of damage to the electronics and computers hooked up to the scanner.

Seriously, it's a huge red button that tempts me every time
I walk into the IRC (imaging research center).

So I think more than ever, whenever I see the huge red button that will kill the magnet- I have to resist all temptation  to push the button.  That's one act of impulse that I simply can't afford.