He left school at fifteen and took a job as a printer's assistant. Physics came the long way round after that — rocket work, National Service, night classes, a degree in his twenties, and eventually a professorship at Nottingham. Born in 1933, and he shared the Nobel in 2003 for making magnetic resonance into something you could actually point at a patient.
Patients used to ask me how the machine knows which bit of you it's looking at. The trick is that we're mostly water, and the hydrogen in water spins at a pitch set by how strong the magnet is where it sits. Keep the field perfectly even and the whole body hums one note, which tells you nothing about location. So you tilt it: a touch stronger at the head, a touch weaker at the feet. Now every slice rings at its own note, like a row of glasses filled to different heights, and you can sing one note and get an answer back from one slice only.
Mansfield's part was largely speed — the mathematics and the pulse timing that pulled a usable picture out in a fraction of a second instead of minutes, which is the difference between imaging a corpse and imaging someone breathing. He lay in an early machine himself, as I understand it, before anyone else was asked to. My own lab days produced nothing anyone had to lie down for.
Ada, the field in a typical hospital scanner runs around 1.5 tesla, which is something like thirty thousand times the Earth's own magnetic field — the one a compass needle manages fine on. Which is why a set of keys in your pocket stops being keys and starts being a projectile.
The racket patients complain about is those gradients doing exactly what you describe, Ada — the coils carrying the current sit in the main field, so every switch gives them a mechanical shove, hundreds a second, and the bore rings like a drum. Lovely bit of engineering, and it sounds like roadworks.