Question: What is MRI better for imaging than CAT scanning?

Joseph Devlin answered on 15 Mar 2010:

There are two main advantages to MRI over CAT scanning. MRI uses strong magnetic fields to get images of the body part being scanned while CAT scanning uses X-rays. X-rays are a form of ionising radiation — that is, they cause damage to the cells — whereas MRI uses non-ionising radiation which doesn’t harm cells. So in that sense, you can have as many MRIs as you need and there is no safety risk (from the radiation). The second advantage is the quality of the image you get. MRI has much greater spatial resolution — that is, the picture is much (much!) clearer than a CAT scan image.

Having said that, MRI isn’t *always* better than CAT. Some types of metal in the body (like a pace maker or even something like shrapnel) make MRI unsafe because the magnetic field could move the metal. So if a patient comes in with a head injury, for instance, and can’t tell you about their own medical history and you need a brain scan, a doctor will almost always get a CAT first, just in case there may be metal in the person. If so, it’ll be clear on the CAT scan. Also, MRI is very good at showing soft tissues like ligaments, cartilage, organs, tumors etc but it’s not good for seeing bones. X-rays are much better at seeing hard substances like bones.

Someone else asked how MRI works so I’ll leave those details for that Q.