MRI and CT both produce detailed, cross-sectional images of the inside of the body, which is why they are easy to confuse. They work in completely different ways, though, and each is better at answering certain questions.
How they work
An MRI uses a strong magnetic field and radio waves, no radiation. It is excellent for soft tissue: joints and ligaments, the spine and discs, the brain, and the abdominal and pelvic organs. A CT scan uses X-rays and is very fast. It is particularly good for fine bone detail, the chest and lungs, and imaging of the heart’s arteries.
Which one for which question
As a rule of thumb, if the question is about soft tissue, MRI is usually the better test; if it is about bone detail, the lungs, or a rapid answer, CT often wins. Frequently the two are complementary rather than competing.
Radiation and referrals
Because CT uses radiation, it must be requested by an entitled referrer. MRI uses no radiation, so you can refer yourself. If you are not sure which scan answers your question, ask us, we would rather point you to the right test than the more expensive one.