What are typical ultrasound frequency choices and the corresponding tissue depths?

• A. 3 MHz for superficial tissues (~1–2 cm); 1 MHz for deeper tissues (~2–5 cm).
• B. 0.5 MHz for deeper tissues (~3–6 cm); 3 MHz for superficial tissues (~1–2 cm).
• C. 1 MHz for deeper tissues (~2–5 cm); 3 MHz for superficial tissues (~0.5–1 cm).
• D. 2.5 MHz for superficial tissues (~0.5–1 cm); 5 MHz for deeper tissues (~3–6 cm).

Answer: (C)

Ultrasound frequency determines how deeply the energy can penetrate: higher frequency is absorbed more quickly and doesn't travel far, while lower frequency penetrates deeper but with less fine detail. In therapeutic practice, a common pairing is to use 3 MHz for superficial tissues, roughly around 0.5 to 1 cm beneath the skin, and 1 MHz for deeper tissues, roughly 2 to 5 cm deep. The option that aligns with this pattern assigns 1 MHz to deeper tissues (2–5 cm) and 3 MHz to superficial tissues (0.5–1 cm). This reflects the practical guideline that deeper targets are treated with the lower frequency, and superficial targets with the higher frequency. Real depth can vary with tissue type and coupling, but these ranges are typical.