Which heating modality uses other forms of energy, such as ultrasound, to produce heat?

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

Answer: (D)

Heating by converting energy from one form into heat inside the tissue is conversion heating. Modalities like ultrasound deliver another form of energy—mechanical energy in this case—and as that energy is absorbed by the tissue, it is transformed into heat, warming the deeper tissues. This is different from conduction, where heat moves directly from a warmer surface to cooler tissue through contact; convection, where heat is carried by moving fluids or air; and radiation, where heat is transferred by waves (like infrared) to the surface. So ultrasound demonstrates conversion heating because it starts with a different energy form and converts it to heat within the body.