Intensity is determined by what?

• A. The medium
• B. The sound source
• C. The transducer frequency
• D. The distance to the reflector

Answer: (B)

Intensity is the energy per unit area carried by the ultrasound beam, and the amount of energy leaving the transducer is set by the sound source. The drive electronics and the transducer’s efficiency determine how much acoustic power is produced, so the initial intensity is determined by the source. Once the wave enters tissue, the medium can attenuate energy as it travels and higher frequencies tend to lose energy more quickly, which changes the intensity along the path. The distance to a reflector affects how much energy is lost on the way to and from that reflector, influencing the received signal, but it does not set the emitted intensity.