In ultrasound therapy, what primarily determines the depth of tissue penetration?

• A. Frequency
• B. Intensity
• C. Duty cycle
• D. Treatment duration

Answer: (A)

Depth of penetration in ultrasound therapy is governed mainly by frequency, because frequency controls how quickly the wave is attenuated as it travels through tissue. Lower frequency waves have longer wavelengths and experience less attenuation, so energy can reach deeper tissues. Higher frequency waves are absorbed more readily, depositing most energy near the surface and limiting depth. That’s why deeper targets are treated with lower frequencies, while higher frequencies are used for superficial tissue. The other factors—intensity, duty cycle, and treatment duration—affect how much energy is delivered and how much heating occurs, but they don’t determine how deep the energy travels.