How does a CT scanner work?

A CT scanner spins an X-ray tube around you three times a second, takes about a thousand shadows each turn, and a computer turns them into slices of your body. Inside the doughnut-shaped gantry, a heavy disc carries an X-ray tube and a curved detector with 64 or more rows of sensors.

Read how it works: How does a CT scanner work? · The history of the CT scanner · More boxes on Glassbox

Chapters in this interactive model

1. Inside a CT scanner: A ring that spins an X-ray tube and a curved camera around you, faster than you can blink.
2. Hundreds of shadows make a slice: The tube spins, each angle casts a shadow, and the table glides through in a spiral.
3. Turning shadows into a picture: Smear every shadow back across the image, but sharpen it first.
4. Hounsfield units and windows: Every pixel is a number. You choose which numbers become grey.
5. How much radiation, and why it’s worth it: A CT scan gives more dose than an X-ray picture, but it is fast and it sees so much more.
6. Two energies, a heartbeat and counting photons: How today’s scanners tell materials apart, freeze a beating heart and count every X-ray.