What is the purpose of curving transducer elements or applying a lens over the elements?

• A. Reduce acoustic impedance mismatch between the crystal and skin
• B. To help reduce electronic interference
• C. Provide focusing in the out-of-plane (elevational) direction
• D. To reduce crystal ringing and improve axial resolution

Answer: (C)

Elevational focusing is achieved by curving the transducer elements or adding a lens, which shapes the emitted wavefront in the elevation (out-of-plane) direction. This creates a converging beam in that axis so the energy is concentrated into a thinner slice at the focal depth. By narrowing the beam across the elevation dimension, the slice thickness improves, and the elevational resolution of the image gets better. The curvature or lens doesn’t primarily change impedance matching, reduce electronic interference, or alter the pulse length; those factors relate to coupling, shielding, and axial resolution, respectively.