Which heating method could ultrasound be categorized under?

• A. Conduction
• B. Convection
• C. Radiation
• D. Conversion

Answer: (D)

Ultrasound heats tissue by converting energy. The device sends high-frequency mechanical waves into the body, and as those waves are absorbed by the tissue, their acoustic energy is transformed into thermal energy through absorption and internal friction. This is a change of energy form—from mechanical (acoustic) energy to heat—which is why it’s categorized as conversion. It isn’t conduction, which transfers heat between neighboring molecules, nor convection, which involves moving fluids carrying heat, nor radiation, which uses electromagnetic waves to transfer energy.