During diagnostic ultrasound, energy is partially converted to heat in tissues. Which factor most directly contributes to this heating?

• A. Refraction
• B. Absorption of sound energy
• C. Scattering
• D. Reflection

Answer: (B)

In diagnostic ultrasound, tissue heating comes from the portion of acoustic energy that is absorbed by the tissue, which is converted into heat through molecular interactions and viscous losses. Refraction, scattering, and reflection affect where the energy goes or how it is distributed, but they do not by themselves convert energy to heat. Absorption directly dissipates the ultrasound energy within the tissue, and the amount of heating depends on how strongly the tissue absorbs the energy, along with how long and how intense the exposure is.