How an MRI scanner works
We cut an MRI scanner open: a superconducting magnet chilled by liquid helium to −269 °C, with gradient coils and a radio coil nested inside. A radio pulse at the protons' own wobble rate, 64 million times a second in a 1.5-tesla scanner, tips the hydrogen in your body over, and as it relaxes it induces a faint signal in the coil. Fat relaxes faster than water, so if you time it right, fat shines while water stays dark. Gradient coils give every spot its own rate (switching them is the loud banging), and a computer turns the frequencies into a slice of you.
- 0:00 The question
- 0:07 The layers
- 0:18 Hydrogen, a tiny magnet
- 0:30 The flip
- 0:39 Signal, then relaxation
- 0:47 Fat vs water
- 0:54 Position, and the banging
- 1:04 The image