How does the choice of coupling medium affect transducer performance and image quality?

• A. It creates air gaps to reduce reflections.
• B. It eliminates air gaps, enabling efficient transmission; poor coupling increases reflections and reduces signal, degrading image quality.
• C. It changes the transmitted frequency to match tissue.
• D. It has no impact on image quality.

Answer: (B)

Effective coupling means filling the interface between the transducer and the skin with a medium that provides a smooth, air-free path for the sound waves. By closely matching the acoustic impedance to tissue, the coupling medium minimizes reflections at the transducer–skin boundary, allowing more energy to enter tissue and return to the probe. When air gaps are present, the large impedance difference causes strong reflections, wasting energy and producing a weaker signal that degrades image quality. With good coupling, energy transmission is efficient, giving stronger signals and sharper images. The coupling medium does not change the transmitted frequency—this is set by the transducer and its drive electronics—so claiming it alters frequency isn’t accurate. And acknowledging its impact is important, because poor coupling directly reduces image quality.