How does the magnet in an MRI work to produce an image?

The human body is made up of billions of atoms, which are the fundamental building blocks of all matter. Inside each atom, the nucleus spins on an axis. Think of the nucleus as a top spinning somewhere off its vertical axis.

In the body, billions of nuclei all randomly spin in every direction. The body has many different types of atoms but for the purposes of MRI, we concern ourselves only with the hydrogen atom. Hydrogen is an ideal atom for MRI because hydrogen's nucleus has a single proton and a rather large magnetic moment. The large magnetic moment means, when placed in a magnetic field, the atom has a strong tendency to line up in the direction of the magnetic field.

The MRI scanner has bore where a strong magnetic field runs straight down the center of the tube where the patient is placed. This way, if a patient is lying on his back in the scanner, the hydrogen protons in his body will line up in one direction, either lining up with the feet or the head. By far, the majority of protons will cancel each other out - in other words, for each proton that is lined up toward the feet, a proton lined up toward the head will cancel it out. Out of every million protons, only a few are not canceled out. This doesn't sound like much. Still, with the sheer number of hydrogen atoms in a person's body that's enough to gives the MRI what it needs to create wonderful images.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.