In Chapter 5 of Biopsychology (9th Edition) you learned about the structural brain imaging technique known as Magnetic Resonance Imaging (MRI). The purpose of this blog post is to instill an even better understanding of how MRI works. This will be accomplished through a brief discussion of how the MRI machine works.
There are three key components to an MRI machine:
1. A large magnetic field.
2. A magnetic pulse.
3. A radiofrequency (RF) signal detector (often called a ‘RF coil’).
The following animation (flash plugin is required) shows you how these three elements interact to generate the RF signal that is detected by the RF coil.
Briefly, the large magnetic field created in an MRI scanner serves to align the axes of rotation of all the hydrogen protons in whatever tissue is placed in the scanner (e.g., the brain). Next, a magnetic pulse is emitted in the scanner that pushes the axes of rotation of the protons out of their common alignment. When that magnetic pulse ends, the protons ‘relax’ back to their common alignment in the large magnetic field. As the protons relax, they release RF energy (this RF energy is often termed the ‘relaxation signal,’ since it occurs during the process of relaxation) that is detected by the RF coil. Because different tissues in the body (and brain) have different amounts of water (whose major constituent is hydrogen), different tissues have different relaxation signal strengths.
Stay tuned for a future post where I will provide a more comprehensive explanation of how functional magnetic resonance imaging (fMRI) works.
Mansfield and Lauterbur won the 2003 Nobel Prize in Physiology/Medicine for their work on the MRI. The Nobelprize.org website has a little game you can play that teaches about the MRI.
Simply Physics. For tons of great information and amusing photos related to the MRI scanner.