Which factors determine ultrasound beam intensity?

• A. Power in the beam and area over which the power is applied
• B. Amplitude and frequency
• C. Wavelength and speed of sound
• D. Time duration of the pulse

Answer: (A)

Intensity is the acoustic power delivered per unit area. So the factors that set the beam’s intensity are the power in the beam and the area over which that power is spread. If you increase the power, the intensity rises; if you spread the same power over a larger area, the intensity decreases. Amplitude and frequency describe the strength and the wave’s characteristics but don’t define intensity in the same direct way. Wavelength and the speed of sound affect how the wave travels and interacts with tissue, not the fundamental measure of power per area. The pulse duration influences how much energy is delivered over time (duty cycle), which can change time-averaged intensity, but the instantaneous beam intensity is determined by power and area.