The concentration of energy in a sound beam is called?

• A. Power
• B. Intensity
• C. Amplitude
• D. Frequency

Answer: (B)

The concept being tested is how energy is quantified in a specific area of a sound beam. Intensity measures how much acoustic power passes through a given area in a given time, so it captures the concentration of energy the tissue experiences at that spot. Power is the total energy per unit time carried by the beam but spread over the cross-sectional area, so a larger beam can have the same power with lower intensity. Amplitude refers to the pressure variation in the wave, which reflects how strong the wave is but doesn’t by itself express energy per unit area. Frequency is the rate of oscillation, not the energy delivery per area. In ultrasound practice, higher intensity means more energy delivered to a small area, which is exactly what is meant by concentration of energy. Therefore, the term is intensity.