The aperture in an ultrasound array refers to the number of active elements.

• A. Bandwidth
• B. Aperture
• C. Elevational resolution
• D. Focal zones

Answer: (B)

Aperture size in an ultrasound array is determined by the number of active elements. The active-element count sets how wide the beam-forming aperture is, and that width directly shapes the beam. More elements create a larger aperture, which makes the beam narrower at the focal depth and improves lateral resolution (and depth of field) in the region you’re imaging. Conversely, using fewer elements widens the beam and degrades lateral resolution.

Bandwidth is about the range of frequencies the transducer can transmit and receive, not how many elements are used. Elevational resolution concerns the thickness of the image slice in the elevational direction, which is influenced by the beam width in that direction, not the basic definition of aperture. Focal zones refer to the regions along the depth where focusing occurs; while aperture affects focusing, it is defined by how many elements are active, not by the concept of focal zones itself. Dynamic aperture techniques can adjust the number of active elements with depth to optimize image quality.