Which imaging modality uses magnetic fields and radio frequency pulses to generate detailed images?

• A. CT
• B. MRI
• C. Ultrasound
• D. X-ray

Answer: (B)

Magnetic resonance imaging uses strong magnetic fields and radiofrequency pulses to generate detailed images. In MRI, a powerful magnet aligns the hydrogen protons in body tissues. A radiofrequency pulse disrupts that alignment, and as the protons relax back, they emit signals that detectors pick up and computers convert into highly detailed cross-sectional images. The varying relaxation properties of different tissues create the contrast seen in the images, with special sequences highlighting anatomy and pathology. Because it does not use ionizing radiation, MRI is especially valuable for soft-tissue visualization such as the brain, spinal cord, joints, and muscles. Safety considerations include potential interactions with metal implants and the use of contrast agents in some studies. In contrast, CT and X-ray rely on ionizing radiation, and ultrasound uses sound waves, each with different strengths and limitations.