The MRI Scanner

You have probably been inside one. Roughly 100 to 150 million people a year lie still inside an MRI scanner, and almost none of them are told what is actually happening around them: a magnet 30,000 times stronger than Earth's own field, cooled to four degrees above absolute zero, hammering out a sound like a car alarm on purpose, thousands of times a second, for exactly twenty minutes.

Other books about this machine are written for radiology students or for one side of an old argument. This one explains the machine itself, and the fight over who invented it, to a reader who has never taken a physics class: 135 figures built for this book, over 243 pages, and every number traced to where it came from.

Inside, you'll find:

• The magnet, sized. 1.5 tesla, held in a bath of 1,000 to 2,000 liters of liquid helium at 4 kelvin - a gas the Earth does not replenish, mined in only a handful of places on the planet.
• The noise, explained. Up to 120 decibels, as loud as a jet at takeoff, made by gradient coils switching hundreds of times a second - not a machine straining, but doing exactly what it was built to do.
• Three people, one prize. A physician, a chemist, and a physicist each did something the machine could not work without. In 2003 the Nobel Assembly gave the prize to two of them. A federal court had already awarded the third man's company $128.7 million - about a hundred times the prize money - six years earlier, for a different reason entirely.
• Who gets scanned, and who doesn't. Japan has about 55 scanners per million people. Most of Africa has fewer than one. The same twenty-minute scan costs $400 in one clinic and $3,000 in another.
• What can go wrong. The oxygen tank pulled across a room in 2001, and why the technologist asks about metal in your body three times before letting you in.

There are no clinical photographs in it - every illustration was drawn for this book and is clearly labeled as such. This is a book about how the machine works and who built it, not a diagnostic manual, and it assumes no science background at all.

A hundred million people a year hold still for twenty minutes inside a machine that never switches off. This book explains what it is listening for.