MRI

One of my friends had to get an MRI this past weekend, and I didn't really understand what an MRI was, so I googled it. As it turns out, MRI scans have a lot to do with physics, particularly magnetism. First of all, I learned that MRI stands for magnetic resonance imaging. MRI machines use magnets and radio waves to create a picture of the inner human body.

The magnets used in MRI machines produce a magnetic field between 0.5 and 2 teslas. There are many different types of atoms in the human body, but MRI machines focus on hydrogen atoms. Hydrogen atoms have a large magnetic moment, so when they are placed in a magnetic field, they line up with the direction of the magnetic field.

All of the hydrogen protons will align with the magnetic field in one direction or the other. The vast majority cancel each other out, but, as shown here, in any sample there is one or two "extra" protons.

These extra protons are what create the images. The MRI machines applies a radio wave frequency that is specific to hydrogen, and these radio waves are directed at the part of the body that is being examined. The atoms in this region of the body then absorb the energy from the radio waves, and this causes them to spin in a different direction. Then when the radio wave frequency is turned off, the hydrogen atoms return to their natural alignment and release their excess stored energy. This release of excess energy is essentially what creates the final image that can help doctors diagnose injuries and other health problems.

(information from http://health.howstuffworks.com/mri7.htm)