Magnetic resonance imaging (MRI) is a very powerful medical imaging technique that has redefined the ways in which physicians literally view the body and disease. Unlike other common forms of imaging, including X-rays and computed tomography (CT or CAT), MRI involves no ionizing radiation so it is much safer for patients, and it is also able to image in any plane. However, the magnetic aspect of MRIs does restrict its use from certain patients, such as those with pacemakers or any kind of metal implant (staples, replaced joints, etc.).

MRI is essentially the same thing as nuclear magnetic resonance (NMR), a very common technique used in chemistry to identify compounds. (In fact, the name was changed to MRI in a clinical setting to avoid scaring patients by the word “”nuclear””.) Recall that each electron has a directional spin. A high-powered magnetic field causes the electrons in the compound (or person) to align, creating an energy difference. When the magnetic field is removed, the electrons will fall back to their original energy (Figure 1, arrows denote electrons).

Often, to improve the contrast quality of the image, such as when assessing for masses or tumors in the brain, radiologists will infused a contrast agent prior to taking the image. Gadolinium-based compounds are the most common.

Figure 1. NMR spin alignment.
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