Which imaging modality uses high-frequency sound waves to produce images?

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

Answer: (C)

Ultrasonography uses high-frequency sound waves to produce images. A transducer emits pulses that travel into the body and then receives the echoes that bounce back from tissue interfaces. By measuring the time it takes for echoes to return and their strength, the system creates real-time images of organs and structures. Doppler techniques can also detect movement, such as blood flow, by observing changes in the frequency of the returning waves.

This modality is radiation-free, making it a preferred choice in pregnancy, pediatrics, and bedside assessments, though image quality can be limited by factors like obesity, overlying gas, or bone. In contrast, X-ray and CT rely on ionizing radiation, and MRI uses magnetic fields and radio waves, not sound, to visualize tissues.