At a tissue-air interface, the transmitted energy is mostly which?

At a tissue-air interface, the transmitted energy is mostly which?

• A. Reflected
• B. Transmitted
• C. Absorbed
• D. Scattered

Answer: (A)

A tissue-air boundary creates a large acoustic impedance mismatch, because air has a very low impedance compared with tissue. When the ultrasound wave hits this boundary, most of the energy cannot enter the air and is reflected back toward the transducer. The transmitted portion into air is very small (only a tiny fraction), so the majority of energy appears as a reflection. This strong reflection is why tissue-air interfaces produce bright echoes and, in many cases, little energy is transmitted beyond the boundary. Absorption and scattering occur, but they are not the dominant effect at this boundary; the key factor is the near-total reflection due to impedance mismatch.

A tissue-air boundary creates a large acoustic impedance mismatch, because air has a very low impedance compared with tissue. When the ultrasound wave hits this boundary, most of the energy cannot enter the air and is reflected back toward the transducer. The transmitted portion into air is very small (only a tiny fraction), so the majority of energy appears as a reflection. This strong reflection is why tissue-air interfaces produce bright echoes and, in many cases, little energy is transmitted beyond the boundary. Absorption and scattering occur, but they are not the dominant effect at this boundary; the key factor is the near-total reflection due to impedance mismatch.