How does the choice of matching layers influence energy transfer from the transducer to tissue?

• A. It blocks energy transfer.
• B. It minimizes reflections and maximizes energy transfer by creating gradual impedance steps.
• C. It has no effect on energy transfer.
• D. It only affects color Doppler.

Answer: (B)

Acoustic impedance matching is the key idea. The transducer crystal has a high acoustic impedance and tissue is much lower, so a large portion of the generated energy reflects at the crystal–tissue boundary if there’s no intermediary. A matching layer sits between the crystal and tissue with an impedance between the two and is often designed to be a quarter-wavelength thick at the center frequency. This creates a gradual impedance transition that minimizes reflections at both interfaces, so more energy is transmitted into tissue rather than bounced back. With the appropriate matching layer (or layers), energy transfer is maximized, improving penetration, signal strength, and overall image quality. This effect applies to all transmitted ultrasound energy, not just color Doppler.