Which sound beam frequency would exhibit the greatest intensity loss with increasing depth?

• A. 2 MHz
• B. 10 MHz
• C. 8 MHz
• D. 5 MHz

Answer: (B)

Attenuation in tissue increases with frequency, so higher-frequency ultrasound loses more of its intensity as it travels deeper. In most tissues, the attenuation coefficient is roughly proportional to frequency, meaning the intensity drops roughly as I(z) ≈ I0 e^{-2αz} with α ∝ f. Among the given options, the highest frequency beam (10 MHz) will therefore experience the greatest loss of intensity with increasing depth. The lower frequencies attenuate less over the same distance, which is why they retain more of their intensity deeper down. This illustrates the trade-off: higher frequency gives better resolution but greater attenuation and shallow penetration.