What is a key difference between CT and MRI in terms of safety and contraindications?

• A. CT uses ionizing radiation and iodinated contrast; MRI uses strong magnetic fields; contraindicated with certain implants and ferromagnetic devices; gadolinium risk in CKD.
• B. CT uses no radiation; MRI uses strong magnetic fields.
• C. CT is contraindicated with implants; MRI is safe with any implant.
• D. CT uses gadolinium contrast; MRI uses iodinated contrast.

Answer: (A)

Safety differences come from how each imaging method interacts with the body. CT uses X-ray beams that deliver ionizing radiation and often iodinated contrast when enhanced imaging is needed. Ionizing radiation carries a small but real cumulative cancer risk, and iodinated contrast can cause allergic reactions or contrast-induced kidney injury in susceptible patients. MRI relies on a strong magnetic field and radiofrequency energy; many ferromagnetic implants or devices are unsafe or require careful evaluation, and when contrast is used it’s gadolinium-based, which can pose a risk of nephrogenic systemic fibrosis in people with advanced kidney disease and has other patient-specific considerations. Some implants today are MRI-conditional, but many devices still limit MRI use or require precaution. The other statements are incorrect because CT does involve radiation and iodinated contrast, MRI is not universally safe with any implant, and gadolinium is not used in CT while iodinated contrast is not used in MRI.