How does an MRI machine work?

A magnet 30,000 times stronger than Earth's, a radio that listens to the hydrogen in your body, and a Fourier transform that turns echoes into a picture. An MRI scanner is a superconducting magnet: coils of niobium-titanium wire bathed in liquid helium at about −269 °C, carrying current with no resistance.

Read how it works: How does an MRI machine work? · The history of MRI · More boxes on Glassbox

Chapters in this interactive model

1. Inside an MRI scanner: A giant magnet that is always on, three coils that tilt its field, and a radio.
2. Your body is full of tiny magnets: Hydrogen nuclei line up, very slightly, and wobble at a radio frequency.
3. A radio pulse, and an echo: Knock the spins over, listen as they fade and recover. Timing sets the contrast.
4. How the scanner knows where: Tilt the field, and frequency tells you position. Then a Fourier transform.
5. The magnet is always on: No X-rays, but a field strong enough to turn a steel cylinder into a missile.
6. Watching the brain work: Blood oxygen, water on the move, and flowing blood, all without X-rays.