Comparison · Imaging study vs Imaging study
CT vs MRI
Both produce cross-sectional images of the body, but by different physics: CT uses X-rays and is fast, MRI uses magnetic fields and radio waves and shows soft tissue in more detail without radiation. The choice depends on the question, the urgency and the patient.
| Aspect | CT scan | MRI scan |
|---|---|---|
| How it works | Rotating X-ray beam and detectors reconstruct slices from tissue density | Strong magnetic field and radio pulses map hydrogen nuclei; sequences highlight different tissue properties |
| Radiation | Yes: a moderate dose that adds up with repeated scans | None |
| Speed | Seconds to a few minutes | 20-60 minutes, lying still in a narrow tunnel |
| Best tissue contrast | Bone, lung, acute bleeding, calcification, contrast-enhanced vessels | Brain, spinal cord, muscle, ligaments, cartilage, pelvic organs, marrow |
| Contrast agents | Iodinated contrast (allergy and kidney precautions; metformin paused) | Gadolinium (avoided in severe kidney impairment) |
| Limitations | Radiation, less soft-tissue detail, iodine contrast risks | Metal implants and devices, claustrophobia, cost and availability, motion |
Where CT scan fits
Emergencies (trauma, stroke within minutes, bleeding, pulmonary embolism), bone and lung detail, people who cannot lie still or have MRI-incompatible implants
Where MRI scan fits
Brain and spinal cord, joints, ligaments and cartilage, the pelvis, liver lesions, and when radiation must be avoided
Educational content. A comparison explains what each test, marker or medicine is for and how they differ. It is educational and does not say which one a person should have; that decision belongs to the clinician who knows the person and the question.