What is the main difference between cat scan and mri?

CT scan uses xrays,: MRI uses magnetic resonance to render images.. Also, CT usually gives a cross sectional view while MRI gives a length like view. There is no radiation from MRI, but because it acts like a super strong magnet,metal must be removed before it is done.

MRI/CT: A CT scan uses x-ray radiation to generate an image. An MRI uses magnetic fields "tuned" to the frequency of protons in the body. Since each scan essentially measures a different property of tissues in the body, they are complementary tests. That is why if one doesn't provide a definitive answer, often the other will be ordered.