3 MHz gets warm faster due to which characteristic?

• A. Superficial treatment
• B. Deeper heating
• C. Higher energy conversion
• D. Lower impedance

Answer: (A)

The key idea is that frequency sets how deep ultrasound energy is absorbed in tissue. A higher frequency like 3 MHz is absorbed more rapidly and over a shorter distance, so most of the energy is deposited in superficial layers. That means the superficial tissues heat up faster with 3 MHz than deeper tissues, making it a choice for near-surface targets. In contrast, deeper heating would come from a lower frequency, such as 1 MHz, which penetrates further before being absorbed. The heating pattern isn’t primarily about more energy being produced; it’s about where the energy is absorbed. Impedance affects coupling at boundaries, but it doesn't determine the depth of heating.