If 3 MHz sound has a 2 dB attenuation in 1 cm of tissue, what is the attenuation of 6 MHz sound in 0.5 cm of the same tissue?

• A. 5 dB
• B. 2 dB
• C. 10 dB
• D. 1.5 dB

Answer: (B)

Attenuation in tissue scales with both frequency and distance along the path, assuming a constant attenuation coefficient. From the given data, 3 MHz attenuates by 2 dB over 1 cm, so the attenuation coefficient is 2 dB per (cm·MHz) = 2/3 dB/(cm·MHz).

Now apply to 6 MHz over 0.5 cm: attenuation = (2/3) × 0.5 × 6 = 2 dB.

An intuitive check: doubling the frequency tends to double attenuation, but halving the distance halves attenuation, so overall the result remains the same in this case.