Which ultrasound frequency is typically used to heat superficial tissues?

• A. 1 MHz
• B. 3 MHz
• C. 5 MHz
• D. 0.5 MHz

Answer: (B)

Heating depth with ultrasound depends on frequency: higher frequency is absorbed more quickly and deposits most of its energy near the surface, while lower frequency penetrates deeper with less surface heating. When you want to heat tissues close to the skin, a frequency around 3 MHz is used because it concentrates energy in the superficial layers (roughly the first centimeter or two). Lower frequencies like 1 MHz would warm deeper tissues, not the surface, and while very low frequencies penetrate even more, they don’t provide efficient superficial heating. A frequency such as 5 MHz would be even more surface-focused, but in typical therapy settings 3 MHz is the standard choice for superficial heating.