Medicine & Health
How does an MRI work?
An MRI works by using a powerful magnet to line up the hydrogen atoms in your body's water, then pulsing radio waves to knock them out of alignment. As the atoms snap back, they emit faint signals that a computer turns into detailed images — with no ionizing radiation involved.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how an MRI works.
Step by step
- 1A strong magnetic field aligns the spin of hydrogen nuclei, which are abundant in the body's water and fat.
- 2A radio-wave pulse tips those nuclei out of alignment, adding energy.
- 3As the nuclei relax back into line, they release radio signals — and different tissues relax at different rates.
- 4A computer maps the signal's strength and timing into cross-sectional images, all without ionizing radiation.
Frequently asked questions
- Is an MRI dangerous like an X-ray?
- No. MRI uses magnetism and radio waves, not ionizing radiation, so it carries none of the radiation exposure of X-rays or CT scans.
- Why is an MRI so loud?
- Rapidly switching 'gradient' coils vibrate against their mountings as strong currents pulse through them, producing the loud knocking sounds.
- Why must you remove metal first?
- The magnet is strong enough to pull ferromagnetic objects forcefully, and metal can heat up or distort the image — so it has to come off.