Which imaging technique uses a magnetic field to create a computerized image of internal bodily structures?

• A. Mammography
• B. MRI (magnetic resonance imaging)
• C. MUGA scan
• D. Muscle biopsy

Answer: (B)

Using a magnetic field to create a computerized image of internal structures is MRI. In MRI, a strong, static magnetic field aligns the protons in the body's water molecules. A radiofrequency pulse tips these protons away from alignment, and as they realign with the field they emit signals that a computer collects and processes into detailed cross-sectional images. Spatial encoding with magnetic field gradients tells the machine exactly where signals come from, so you get precise pictures of soft tissues like the brain, spine, muscles, and ligaments. Contrast agents may be used to improve visibility of specific tissues.

Other options work differently: mammography uses X-rays to image tissue and involves ionizing radiation, not a magnetic field. A MUGA scan relies on a radioactive tracer and a gamma camera to assess heart function. A muscle biopsy is an invasive procedure that removes tissue for direct examination rather than producing an image.