How does the intensity of high-frequency ultrasound change as it passes through the body?

• A. Increased uniformly
• B. Reduced by different amounts depending on acoustic properties of tissues through which they travel
• C. Oscillates
• D. Remains constant

Answer: (B)

As ultrasound travels through the body, its intensity drops because tissues absorb and scatter part of the energy. Different tissues have different attenuation properties, so the amount of energy lost varies with what the beam passes through. In addition, higher frequencies attenuate more quickly, so the beam’s intensity decreases more as it encounters tissues with higher attenuation. A simple way to think about it is I(x) = I0 e^{-αx}, where α depends on both tissue type and frequency. This is why the transmitted intensity is reduced by varying amounts across different tissues. The beam does not increase in strength, oscillate, or stay constant.