In therapeutic ultrasound, what depth is typically targeted by a 3 MHz frequency?

• A. Up to 0.5 cm
• B. 3–5 cm
• C. 5–7 cm
• D. 1–2 cm

Answer: (D)

The main idea is that frequency controls how deep ultrasound energy penetrates tissue. Higher frequencies are absorbed more quickly, so they heat and affect only superficial tissues. A 3 MHz transducer concentrates most of its energy within roughly 1–2 cm beneath the skin, making it suited for superficial structures. Deeper targets (several centimeters down) require lower frequencies, like 1 MHz. That’s why 3 MHz is paired with a shallow treatment depth of about 1–2 cm.