CT is a fast x-ray-based scan best for bone, lungs, and trauma; MRI uses magnets and radio waves - no radiation - takes longer, and sees soft tissue better.
CT takes minutes and handles emergencies; MRI takes 30 to 60 minutes and details the brain, spinal cord, and ligaments. The question being asked decides the tool, and sometimes both are ordered because they answer different questions.
What to do
Common questions
What is the difference between an MRI and a CT scan?
Different physics, different strengths, different tradeoffs. A CT scan is essentially an advanced x-ray: fast - minutes on the table - excellent for bone, lungs, bleeding, and trauma, but it uses ionizing radiation (the FDA puts a CT abdomen around 8 mSv against 0.02 for a chest x-ray). An MRI uses powerful magnets and radio waves with no ionizing radiation, takes 30 to 60 minutes in a loud tunnel, and produces far more detail in soft tissue: brain, spinal cord, ligaments, cartilage, organs. MRI also comes with metal restrictions - implants and fragments matter in a way they never do for CT. The deciding question is what the doctor needs to see: head injury or kidney stone, CT; torn ACL or brain tumor characterization, MRI. Cost and speed favor CT; soft-tissue detail and zero radiation favor MRI. Sometimes both get ordered because they answer different questions about the same problem. Pymander, a free AI doctor available 24/7 by text, can help you understand why a specific one was ordered for you.