Science Interviews


Sun, 11th Feb 2007

Using Radiation in Medicine

Dr Anant Krishnan, Addenbrookes Hospital, Cambridge

Part of the show Nuclear Power

Chris - Now we're going to talk about the science of radiology. From Addenbrookes Hospital in Cambridge here's Anant Krishnan. Now you're a radiologist and that means you use radiation for medical purposes. It must make a big difference to doctor's lives.

Anant - Absolutely. It helps with both the diagnosis and treatment of disease and it's revolutionised the way things are going. Things are only going to get better now.

Chris - They're a bit dangerous though aren't they, x-rays?

Anant - You would think so, but it's about using it responsibly. If I can just put it in perspective, if you have a chest x-ray, the lifetime risk of developing a fatal cancer is less than being killed by a bolt of lightning.

Chris - But can you put some figures on it in terms of how much excess radiation I'm getting through having a chest x-ray because people say it's the equivalent of going out in the sun for three days or something.

Anant - It's getting about ten day's worth of background radiation.

Chris - But that's a simple chest x-ray. What about when you have more complicated procedures like abdominal x-rays or a CT scan?

Anant - CT scans do give more radiation, but you have to balance the benefits versus the risks. If I use the same analogies as before, having an abdominal CT would have the same lifetime risk of developing a fatal cancer as dying from an accident at work.

Chris - How does an x-ray actually work? When we've got someone and image their internal organs, how does that actually work?

Anant - Well first of all we create the x-rays by accelerating electrons at a metal target and that interaction gives off the x-rays, and we can then target that at the part of the body we want to image.

Chris - Because x-rays are a form of light aren't they, just with a short wavelength.

Anant - It's part of the electromagnetic spectrum, so it's a different part of the spectrum. What we do is target it at the body and it can do one of two things: it can either go through or interact with the soft tissue or the bone. It's the x-rays that go through and we can detect that on the x-ray plate, so we develop a shadow of what's going on in the body.

Chris - So some parts of the body mop up the x-rays more than others, and this is what gives you an image?

Anant - Heavier atoms tend to absorb more of the x-rays, so bone obviously.

Chris - Calcium.

Anant - Yes.

Chris - So what about when you want to do more complicated things, because obviously an x-ray is just literally zapping someone straight through. What about if you want to build a three-dimensional picture with say CT? How does that work?

Anant - Well that's using the same sort of thing, except that you're firing x-rays from different angles. That's then being picked up by a computer so that you get a 3D reconstruction. But everyone talks about x-ray and CT, when radiology also uses non-ionising radiation as well, so ultrasound and MRI. So these are much safer forms of radiation as well.

Kat - There are some people that suggest you should have a full-body CT scan every year, and some people in America do. Is that a good idea?

Anant - I don't actually think so because again you're looking at giving someone a radiation dose and it's not without its own risks, as has been made quite clear today. So we have to look at whether the benefits of doing the test outweigh the risks of getting something as an adverse effect.


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