Amplitude is initially determined by the sound source; as the sound propagates through the body, amplitude ____.

• A. Remains constant
• B. Increases
• C. Varies randomly
• D. Decreases

Answer: (D)

As sound travels through the body, its amplitude decreases due to attenuation. Tissues absorb part of the energy and scatter the rest, and the wave’s energy spreads over a larger area as it propagates, which lowers the pressure amplitude at greater depths. Boundaries between different tissues can also reflect some energy, further reducing the forward amplitude. So, as distance from the source increases, the amplitude diminishes. The amount of attenuation depends on tissue properties and the ultrasound frequency—higher frequencies are attenuated more quickly, making the decrease more pronounced. This isn’t a matter of constant, increasing, or random variation; it follows a predictable pattern of energy loss with distance and tissue characteristics.