A frequency of what is used for heating superficial with depth less than 2 cm?

• A. 1.0 MHz
• B. 3.0 MHz
• C. 2.0 MHz
• D. 5.0 MHz

Answer: (B)

When using therapeutic ultrasound, the frequency determines how deep the energy is absorbed. Higher frequency heats tissues closer to the surface, while lower frequency penetrates deeper. For targets at a depth up to about 2 cm, a frequency around 3 MHz is ideal because it concentrates heating in the superficial to near-superficial layers without reaching much deeper tissues. A lower frequency like 1.0 MHz would reach deeper structures than intended, and a higher frequency like 5.0 MHz would heat only the very surface, possibly not reaching the full 2 cm depth. So 3.0 MHz provides the proper balance to heat tissues within that shallow depth.