What does frequency determine?

• A. Depth of penetration
• B. Beam width
• C. Acoustic impedance
• D. Tissue perfusion

Answer: (A)

The main idea is that frequency sets how deeply ultrasound can travel before it gets attenuated. Higher frequencies attenuate more quickly in tissue, so they don’t reach as far, giving better resolution up close but shallower penetration. Lower frequencies travel farther because they attenuate more slowly, though with lower resolution. So frequency largely determines how deep the ultrasound can image.

Beam width depends mainly on the transducer’s aperture and focusing, not frequency alone. Acoustic impedance is a property of the tissue (density times sound speed) and doesn’t change with frequency. Tissue perfusion is about blood flow and physiology, not the frequency of the ultrasound.