Ability to distinguish two structures along a path parallel to the sound beam is called

• A. Aperture
• B. Apodization
• C. Array
• D. Axial Resolution

Answer: (D)

Axial resolution is the ability to distinguish two structures located along the direction of the sound beam. This separation is limited by the spatial pulse length, which equals the number of cycles in the pulse times the wavelength. Shorter pulses—achieved with higher-frequency transducers or by using shorter-duration pulses with fewer cycles—produce better axial resolution, so two closely spaced interfaces along the beam can be seen as separate echoes rather than a single combined one. In practice, axial resolution is roughly half the spatial pulse length, so reducing either the number of cycles or the wavelength makes finer axial detail possible.

Aperture, apodization, and array refer to how the beam is formed and shaped: aperture affects beam width and thus lateral resolution, apodization reduces side lobes to improve image quality, and an array is a configuration of multiple elements used for steering and focusing. These influence resolution across the beam or in other directions, but the specific ability to separate structures along the beam’s path is governed by axial resolution.