How is a CT scan and an MRI different?

MRI vs CT. The main difference is that CT uses ionizing radiation and MRI uses radiowaves (non-ionizing radiation). It is the ionizing radiation that causes injury to the DNA and potential to develop a cancer down the road. In general, CT is good at looking a differences in radiation absorption (x-ray density). MRI is good at looking at subtle chemical differences (water and fat) in tissues.