What is the primary consequence of impedance mismatch at transducer-tissue interfaces?

• A. Increased transmitted energy with higher sensitivity.
• B. Reflections at interfaces reduce transmitted energy, sensitivity, and bandwidth.
• C. No effect on energy or imaging.
• D. Only affects color display.

Answer: (B)

When a sound wave meets a boundary where the acoustic impedance differs between the transducer and the tissue, part of the energy reflects back and part transmits forward. The bigger the impedance difference, the more energy is reflected and the less energy enters the tissue. This loss of transmitted energy means weaker echoes from deeper or smaller structures, so sensitivity drops. It also harms bandwidth because the reflected energy and the resulting ringing at interfaces distort the pulse and limit the range of frequencies that effectively propagate, reducing image quality. That’s why coupling and matching layers are used to minimize mismatch and keep energy moving into tissue, boosting both penetration and the clarity of echoes.