Which phenomenon occurs when sound direction changes as it crosses a boundary between media?

Which phenomenon occurs when sound direction changes as it crosses a boundary between media?

• A. Reflections
• B. Refraction
• C. Shadowing
• D. A-Mode

Answer: (B)

Refraction occurs when ultrasound travels from one tissue into another with a different speed of sound, causing the beam to bend as it enters the second medium. According to Snell’s law, the transmitted angle changes based on the speed ratio, so the path is no longer straight. If the second medium is slower, the beam bends toward the normal; if faster, away from the normal. This bending affects where structures are imaged and can shift the apparent position of features. This is different from reflections, which send energy back to the transducer and create echoes at interfaces; shadowing, which results from strong attenuation behind a structure; and A-Mode, which is a one-dimensional depth display rather than a change in beam direction.

Refraction occurs when ultrasound travels from one tissue into another with a different speed of sound, causing the beam to bend as it enters the second medium. According to Snell’s law, the transmitted angle changes based on the speed ratio, so the path is no longer straight. If the second medium is slower, the beam bends toward the normal; if faster, away from the normal. This bending affects where structures are imaged and can shift the apparent position of features. This is different from reflections, which send energy back to the transducer and create echoes at interfaces; shadowing, which results from strong attenuation behind a structure; and A-Mode, which is a one-dimensional depth display rather than a change in beam direction.