In which medium is there no noticeable attenuation of ultrasound frequencies below 10 MHz?

In which medium is there no noticeable attenuation of ultrasound frequencies below 10 MHz?

• A. Water
• B. Air
• C. Bone
• D. Fat

Answer: (A)

Attenuation in ultrasound comes from absorption and scattering, and it increases with frequency. Water has extremely low acoustic absorption and scattering at diagnostic frequencies, so ultrasound below 10 MHz experiences essentially no noticeable loss as it travels through water. That makes water effectively transparent to these frequencies over typical distances, which is why it's used as a coupling medium in many experiments and imaging setups. In contrast, air introduces a large impedance mismatch and high energy loss, bone causes strong absorption and scattering due to its dense, heterogeneous structure, and fat, while better than bone, still attenuates more than water.

Attenuation in ultrasound comes from absorption and scattering, and it increases with frequency. Water has extremely low acoustic absorption and scattering at diagnostic frequencies, so ultrasound below 10 MHz experiences essentially no noticeable loss as it travels through water. That makes water effectively transparent to these frequencies over typical distances, which is why it's used as a coupling medium in many experiments and imaging setups. In contrast, air introduces a large impedance mismatch and high energy loss, bone causes strong absorption and scattering due to its dense, heterogeneous structure, and fat, while better than bone, still attenuates more than water.