Which transducer type has the same measurement for elevational and lateral resolution?

• A. Convex linear array
• B. Phased linear array
• C. Annular array
• D. Mechanical sector

Answer: (C)

In ultrasound, how sharp the image is in two transverse directions depends on the beam width in those directions. An annular array uses concentric rings, forming a circular aperture that can be focused symmetrically in both the lateral and elevational directions. This circular symmetry produces a beam that remains similarly narrow in both transverse dimensions at the focal region, so the lateral and elevational resolutions come out about the same.

Other transducers tend to have different beam shapes: linear arrays and phased arrays focus mainly in the lateral direction with the elevational dimension set by the element height, often giving finer lateral than elevational resolution; a mechanical sector has fixed geometry that typically leads to differing resolutions between directions.