06/04/2014
Hump Day Highlight: MRI Machines!
Much of our research uses an MRI machine to take various images of brains and bodies. But what is the machine itself?
An MRI is essentially a massive magnet. Modern MRI magnet strengths can be anywhere between 1.5 and 9 Tesla. For comparison, the Earth’s magnetic field is just 30 microtesla, or .00003 Tesla - that means the MRI field is about 100,000 times stronger than the Earth’s! Basic magnets like the ones that come in toys or stick on your refrigerator could never be this strong even at the size of the MRI. Instead, the MRI uses a superconducting material that is cooled to temperatures under -400ºF using liquid helium. When the material is brought to this temperature, special properties of the material cause it to become powerfully magnetic.
To take the images of your brain, we use a radio frequency system. This system transmits electromagnetic waves at very slow, low energy wavelengths. When these waves collide with particles in the body, typically water or hemoglobin, they cause a select few atoms to be “excited”, effectively giving them a tiny bit of extra energy for a brief period. These excited atoms then release this extra energy as a similar electromagnetic wave when they return to the baseline, or “ground state”. The radio frequency system can record this released wave among the many others released after excitation.
To make the images make sense in 3-D space, we use a second magnet, called the gradient magnetic field. This field can be turned on and off in rapid cycles to produce different magnetic field strengths in different locations. This causes different amounts of energy to be released by particles in different places in the brain. We can then use our knowledge of what energy levels were applied in what places to determine which signals came from which locations. These three components together, then, are able to produce the 3-dimensional images you see in an MRI image.
Check out just how strong an MRI magnetic field can be, and what happens when you take metal near the scanner, in the video below! If you are having trouble imagining how much force they are measuring, consider this: 300 pounds of force applied to the side of the wrench in the video would be similar to a grizzly bear sitting on the end of a pencil!
https://www.youtube.com/watch?v=6BBx8BwLhqg
UPDATE: Questions about why we were doing what we were doing? Please see the FAQ under "MRI magnet quench: the movie." That video is also entertaining, btw. ...
