For a 3.0 MHz ultrasound beam at 1.5 W/cm^2, the majority of ultrasound energy is absorbed at which depth?

The majority of ultrasound energy from a 3.0 MHz beam is absorbed at a depth of 1 to 2 cm. This is primarily due to the frequency of the ultrasound. As frequency increases, tissue absorption also increases. At higher frequencies like 3.0 MHz, the ultrasound waves have a shorter wavelength and tend to be absorbed by tissues more effectively at shallower depths.

In clinical applications, lower-frequency ultrasound (e.g., 1 MHz) penetrates deeper (up to 5-6 cm) but is absorbed less, making it suitable for deeper tissue treatments. In contrast, higher frequency ultrasound penetrates less deeply but provides more energy absorption at the surface and shallow layers of tissue. This characteristic is particularly useful when targeting superficial tissues for therapeutic effects, such as in cases of muscle injuries or tendon inflammation.

Therefore, when using 3.0 MHz ultrasound, the optimal therapeutic effects are generally achieved at depths of 1 to 2 cm, making this choice the most appropriate for the question presented.