How Magnetic Resonance Imaging (MRI) Works

One of the many modern diagnostic tools available to medical doctors is magnetic resonance imaging (MRI). MRI scans provide physicians a view of the interior of the patient's body without harming or invading the patient's body in any way. Magnetic resonance imaging is based on the fundamental physics of nuclear magnetic resonance (NMR). How does MRI work?

Nuclear Magnetic Resonance

Nuclear magnetic resonance is an effect that occurs when the nucleus of an atom is placed in a magnetic field. The spinning nucleus in a constant magnetic field wobbles just like a spinning top.

If in addition to the constant magnetic field, there is another magnetic field that varies at the same frequency as the nucleus wobbles, the nucleus will flip back and forth so that the nucleus effectively alternates the direction in which it spins. As the nucleus flips its spin direction, it either absorbs or emits low energy radio waves. Studying these radio waves allows physicists to deduce various properties of the atomic nuclei undergoing NMR.

Safety of NMR and MRI

Nuclear magnetic resonance uses the word nuclear because it involves the nucleus of the atom. It does not however in any way involve any dangerous radiation as people expect from nuclear weapons or other nuclear reactions. The only radiation patients are exposed to by nuclear magnetic resonance imaging is very low energy radio waves. Nuclear magnetic resonance imaging is therefore very safe. The word nuclear was dropped however to allay patient fears. To the average person magnetic resonance imaging sounds less dangerous than nuclear magnetic resonance, and MRI is very safe.

Magnetic Resonance Imaging

Magnetic resonance imaging is a very useful application of NMR. Medical MRI machines are designed to image the nuclei of the hydrogen atoms in the human body. Human bodies contain a high percentage of water, so there are a large number of hydrogen atoms in all human tissue. X-rays image bones well, but image other tissues very poorly. Magnetic resonance imaging therefore provides medical personnel with much better images of the soft tissue in the patient's body than X-rays can provide.