Which imaging modality uses sound waves and does not involve ionizing radiation?

• A. X-ray
• B. Ultrasonography
• C. MRI
• D. CT scan

Answer: (B)

The imaging modality that uses sound waves and does not involve ionizing radiation is ultrasonography. It works by emitting high-frequency sound waves from a transducer into the body. When these waves encounter tissues, they are reflected back to the transducer as echoes whose timing and strength are used to build an image. Because this process relies on sound, not ionizing photons, there is no exposure to ionizing radiation.

This makes ultrasound especially useful when radiation exposure should be avoided or minimized, such as in pregnancy, pediatrics, or when repeated imaging is needed. It provides real-time images and is excellent for evaluating soft tissues, liver, kidneys, gallbladder, abdomen, pelvic organs, and vascular flow with Doppler.

However, its effectiveness can be limited by things like gas in the intestines or dense bone, which impede sound wave transmission. The quality of the study also depends on the operator’s technique and experience. In contrast, X-ray and CT use ionizing radiation, while MRI uses magnetic fields and radiofrequency energy, not sound waves (and does not involve ionizing radiation either).