What is the general term for phenomena that weaken the ultrasound beam?

• A. Attenuation
• B. Refraction
• C. Diffraction
• D. Reflection

Answer: (A)

Attenuation is the general term for phenomena that weaken the ultrasound beam as it travels through tissue. As the wave propagates, part of its energy is absorbed by the medium (often turning into heat) and part is scattered by structures within the tissue, while the wave also spreads out, all of which reduce the forward amplitude and intensity. Attenuation increases with depth and with higher frequencies, since more energy is lost per centimeter at higher frequencies. This is different from refraction, which is the bending of the wave at interfaces due to speed changes; diffraction, which is the spreading and bending of waves around obstacles or apertures; and reflection, which is energy that is redirected back toward the transducer at boundaries.