A 1 MHz ultrasound beam tends to do what in tissue?

A 1 MHz ultrasound beam tends to do what in tissue?

• A. Spread out and dissipate
• B. Focus tightly
• C. Heat only the surface
• D. Be absorbed immediately at the skin

Answer: (A)

When ultrasound frequency changes, how it behaves in tissue changes as well. A 1 MHz beam has a longer wavelength, so it diffracts more as it travels. That means the energy spreads over a larger area and the intensity at any given depth decreases more quickly with distance. Because attenuation grows with frequency, a lower-frequency beam doesn’t get absorbed as quickly per centimeter, but it does lose its focus due to spreading. So, a 1 MHz beam tends to spread out and dissipate rather than staying tightly focused.

When ultrasound frequency changes, how it behaves in tissue changes as well. A 1 MHz beam has a longer wavelength, so it diffracts more as it travels. That means the energy spreads over a larger area and the intensity at any given depth decreases more quickly with distance. Because attenuation grows with frequency, a lower-frequency beam doesn’t get absorbed as quickly per centimeter, but it does lose its focus due to spreading. So, a 1 MHz beam tends to spread out and dissipate rather than staying tightly focused.