What is the force exerted by the sound beam on an absorber or reflector?

What is the force exerted by the sound beam on an absorber or reflector?

• A. Radiation Force
• B. Spatial Average
• C. Ex Vivo
• D. In Vivo

Answer: (A)

Acoustic radiation force is the force exerted by the sound beam on an absorber or reflector. A sound wave carries momentum, and when it encounters an object, momentum is transferred to that object through absorption and scattering. This transfer creates a small, but measurable, push on the absorber or reflector. The strength of this force depends on how the beam interacts with the material—the force is larger when the boundary reflects more of the wave’s energy (momentum change is greater) and can be somewhat smaller when energy is primarily absorbed. This phenomenon is the basis for methods like acoustic radiation force imaging, where a brief, focused high-intensity beam induces localized tissue displacement that can be tracked to assess stiffness. The other terms don’t describe a force: spatial average is a measurement concept over a region, while ex vivo and in vivo describe where a sample exists (outside a living organism vs inside a living organism), not the act of pushing on a target.

Acoustic radiation force is the force exerted by the sound beam on an absorber or reflector. A sound wave carries momentum, and when it encounters an object, momentum is transferred to that object through absorption and scattering. This transfer creates a small, but measurable, push on the absorber or reflector. The strength of this force depends on how the beam interacts with the material—the force is larger when the boundary reflects more of the wave’s energy (momentum change is greater) and can be somewhat smaller when energy is primarily absorbed. This phenomenon is the basis for methods like acoustic radiation force imaging, where a brief, focused high-intensity beam induces localized tissue displacement that can be tracked to assess stiffness. The other terms don’t describe a force: spatial average is a measurement concept over a region, while ex vivo and in vivo describe where a sample exists (outside a living organism vs inside a living organism), not the act of pushing on a target.