MRI uses an interaction of ______ and ______ with tissues.

• A. Magnetic fields and radio waves
• B. X-rays and gamma rays
• C. Sound waves and light
• D. Electrons and photons

Answer: (A)

MRI relies on interactions with magnetic fields and radiofrequency energy to study tissues. A strong static magnetic field aligns the hydrogen nuclei in the body, creating a net magnetization. Then a brief radiofrequency pulse at the appropriate frequency perturbs this alignment; when the pulse stops, the protons relax back and emit signals that are detected by coils. The way different tissues relax (their T1 and T2 properties) and their proton density shape the image contrast. This approach uses non-ionizing magnetic fields and RF energy, unlike X-rays or gamma rays, which are ionizing. It also isn’t based on sound waves or visible light, or on electrons and photons as the primary imaging interaction.