Which statement best describes the role of a density change at a boundary in ultrasound?

Which statement best describes the role of a density change at a boundary in ultrasound?

• A. It can cause refraction of the transmitted energy
• B. It prevents any energy crossing the boundary
• C. It makes energy pass without any change
• D. It only affects color of the image

Answer: (A)

When a wave moves from one tissue to another with a different density, the acoustic impedance changes. This causes the transmitted energy to bend as it enters the second medium—a refraction effect. Some energy is also reflected at the boundary, but energy does cross into the new tissue. The idea that energy would cross without any change or that density changes only affect color isn’t correct; the boundary primarily governs refraction and the split between transmitted and reflected energy.

When a wave moves from one tissue to another with a different density, the acoustic impedance changes. This causes the transmitted energy to bend as it enters the second medium—a refraction effect. Some energy is also reflected at the boundary, but energy does cross into the new tissue. The idea that energy would cross without any change or that density changes only affect color isn’t correct; the boundary primarily governs refraction and the split between transmitted and reflected energy.