As frequency increases, what happens to the attenuation coefficient in soft tissue?

• A. It decreases
• B. It increases
• C. It remains the same
• D. It becomes negative

Answer: (B)

As frequency rises, the attenuation coefficient in soft tissue increases. In ultrasound, the attenuation coefficient α is roughly proportional to frequency, so higher frequency waves lose more energy per centimeter traveled. This happens because both absorption (conversion of acoustic energy to heat) and scattering become more pronounced as frequency increases, since there are more acoustic cycles interacting with the tissue’s microstructure in a given distance. The practical upshot is that higher frequencies give better image resolution but less penetration, since more energy is attenuated per centimeter. For soft tissue, a typical value is about 0.5 to 1.0 dB per cm per MHz, so doubling the frequency roughly doubles the attenuation per centimeter.