Physics 2000 Einstein's Legacy CAT Scans

X-Ray Scanning

So how do we look at the inside of something?

Instead of using a regular "visible light" spotlight, let's start using a special top-secret Pentagon "x-ray spotlight." X-rays don't get absorbed as easily as visible light rays do.

Yeah, some x-rays get through, depending upon what they're going through.


Use the mouse to click and drag the box around in a circle.
Press the "Scan" button to make an x-ray shadow.

This time we will "scan" an object using a beam of x-rays. We will see where the box is "thick" on the inside by how bright the x-rays are on the other side. Just to keep things simple, we'll use a basic box with a rectangle inside it, but you can imagine it's a fruitcake with a single nut inside.

Aha! Just like I said, it's easier to rotate the thing you're looking at rather than the whole machine.

You're right. However, real CAT scan machines rotate around in a circle, while the person being CAT scanned lies still. But if you think about it, spinning the machine is exactly the same as spinning the person. It's just that machines don't get dizzy (or sick...).

And every time I turn it I get a slightly different shadow. But how am I supposed to keep track of all this in my head? If I couldn't actually see inside the box, I would have no idea what I was looking at!

That's where the computer comes in handy.



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