1-MHz ultrasound heats tissue to a depth of

• A. 1-2 cm.
• B. 3-5 cm.
• C. 6-8 cm.
• D. 8-12 cm.

Answer: (B)

Lower frequency ultrasound penetrates deeper into tissue because it experiences less attenuation per centimeter. At 1 MHz, the energy reaches deeper layers before being absorbed, so heating occurs in tissues several centimeters below the surface. In clinical practice, 1-MHz ultrasound typically heats to about 3 to 5 cm beneath the skin, with some variation based on tissue properties, coupling, and intensity. That makes 3–5 cm the best match for the expected heating depth. The shallower 1–2 cm range aligns more with higher frequencies (like 3 MHz), while depths like 6–12 cm exceed the typical therapeutic range for standard ultrasound.