What absorbs the most energy during therapeutic ultrasound?

• A. Deep muscles
• B. Superficial bones and nerves
• C. Cartilage
• D. Blood vessels

Answer: (B)

The main concept is that energy absorption in therapeutic ultrasound is driven by tissue properties, especially attenuation and impedance. Cortical bone has a high density and mineral content, giving it a high acoustic impedance and a high attenuation coefficient. When the ultrasound beam hits bone, most of the energy is absorbed rather than transmitted, causing a rapid temperature rise at or near the bone surface. This makes superficial bones the tissues that absorb the most energy. Nerve tissue by itself doesn’t absorb as much energy as bone, and soft tissues like cartilage or blood vessels have even lower attenuation, so they absorb less energy than bone.