Adipose tissue has what kind of effect on ultrasound?

• A. High
• B. Moderate
• C. Little
• D. No effect

Answer: (C)

Adipose tissue has relatively low attenuation compared with other tissues, so it doesn’t absorb or scatter ultrasound energy very much. In therapeutic ultrasound, fat allows the sound wave to pass through with only a small loss of intensity per centimeter, especially at the common treatment frequencies (around 1–3 MHz). Because of this, a layer of fat isn’t a strong barrier to the beam, which is why its effect is described as little. By contrast, denser tissues like muscle attenuate more and bone attenuates even more, which is why they have a greater impact on ultrasound propagation. If the fat layer were very thick or a higher frequency were used, attenuation would increase, but it still remains less than that of muscle or bone, so the best description stays that adipose tissue has little effect.