Which medium among the following has the lowest attenuation for ultrasound?

Which medium among the following has the lowest attenuation for ultrasound?

• A. Air
• B. Water
• C. Liver
• D. Lung

Answer: (B)

Attenuation describes how ultrasound loses energy as it travels, mainly through absorption and scattering. Water is nearly transparent to diagnostic ultrasound, with very low absorption, so the wave preserves most of its energy as it propagates. Air, however, creates a huge impedance mismatch with tissue, causing most of the energy to reflect at interfaces and be quickly attenuated; it essentially blocks transmission. The lung contains air pockets, leading to similar high attenuation due to scattering and energy loss. The liver, being soft tissue, absorbs more than water but less than air-containing media, so its attenuation sits between water and the more troublesome media. Therefore water has the lowest attenuation among the options.

Attenuation describes how ultrasound loses energy as it travels, mainly through absorption and scattering. Water is nearly transparent to diagnostic ultrasound, with very low absorption, so the wave preserves most of its energy as it propagates. Air, however, creates a huge impedance mismatch with tissue, causing most of the energy to reflect at interfaces and be quickly attenuated; it essentially blocks transmission. The lung contains air pockets, leading to similar high attenuation due to scattering and energy loss. The liver, being soft tissue, absorbs more than water but less than air-containing media, so its attenuation sits between water and the more troublesome media. Therefore water has the lowest attenuation among the options.