The ERA is determined by the

The ERA is determined by the

• A. The outer boundary of the transducer
• B. The depth of tissue penetration
• C. The maximum power setting on the unit
• D. Diameter of the crystal in the transducer

Answer: (D)

ERA is the portion of the transducer surface that actually emits ultrasound energy. It is set by the crystal’s size—the diameter of the crystal determines the effective radiating area. This radiating surface is used to calculate intensity (I = power divided by ERA), so a larger crystal increases ERA and changes the delivered intensity for the same power. The outer boundary of the transducer isn’t the radiating area, the depth of tissue penetration is determined by frequency and tissue properties rather than ERA, and the maximum power setting affects total energy, not the actual radiating surface.

ERA is the portion of the transducer surface that actually emits ultrasound energy. It is set by the crystal’s size—the diameter of the crystal determines the effective radiating area. This radiating surface is used to calculate intensity (I = power divided by ERA), so a larger crystal increases ERA and changes the delivered intensity for the same power. The outer boundary of the transducer isn’t the radiating area, the depth of tissue penetration is determined by frequency and tissue properties rather than ERA, and the maximum power setting affects total energy, not the actual radiating surface.