No, except for the fact that they both use computers and they are both used for medical diagnosis, they really have very little in common. One of the most important differences between a CAT scan and an MRI is the fact that CAT scans use X-ray radiation and MRI scans do not, they use radio waves.
As you probably already know, X-rays can be harmful and it is important therefore to avoid unnecessary exposure to them. Although there are still some situations in which a CAT scan should be used instead of an MRI – your physician will be able to tell you when this is the case and why, for the most part, MRIs are diagnostically superior, especially if soft tissue is involved. If a CAT scan and an MRI are diagnostically equivalent in a particular situation, an MRI is the better choice because it will not subject you to any ionizing radiation. Instead, MRIs use harmless radio waves.
In addition to the superior portrayal of soft tissue, MRIs provide much more flexibility in portraying cross-sectional planes of the body. Unlike a CAT scanner which is relatively limited when it comes to plane selection, an MRI can provide a cross-sectional image taken at any plane in the human body.