Which tissue has the lowest speed of sound among the listed tissues?

Which tissue has the lowest speed of sound among the listed tissues?

• A. Lung tissue
• B. Soft tissue
• C. Fat tissue
• D. Liver tissue

Answer: (A)

The speed of sound in tissue is set by how stiff the tissue is and how easily it can be compressed. In physics terms, ultrasound speed tends to increase with stiffness and decrease with compressibility. Most soft tissues and organs are fairly dense and not highly compressible, so their speeds are around 1500 m/s to 1600 m/s. Lung tissue, however, contains a lot of air. Air is highly compressible and has a very low acoustic impedance, so the sound wave slows dramatically as it passes through the air-filled spaces and interfaces between air and tissue. This makes the effective speed through the lung much lower than through solid tissues like fat, soft tissue, or liver. So, among the options, lung tissue has the lowest speed of sound because its air-filled structure dramatically reduces how fast sound can propagate compared with the other tissues.

The speed of sound in tissue is set by how stiff the tissue is and how easily it can be compressed. In physics terms, ultrasound speed tends to increase with stiffness and decrease with compressibility. Most soft tissues and organs are fairly dense and not highly compressible, so their speeds are around 1500 m/s to 1600 m/s.

Lung tissue, however, contains a lot of air. Air is highly compressible and has a very low acoustic impedance, so the sound wave slows dramatically as it passes through the air-filled spaces and interfaces between air and tissue. This makes the effective speed through the lung much lower than through solid tissues like fat, soft tissue, or liver.

So, among the options, lung tissue has the lowest speed of sound because its air-filled structure dramatically reduces how fast sound can propagate compared with the other tissues.