Elevational resolution is primarily determined by the beam width in which direction?

• A. Along the axial direction
• B. Perpendicular to the imaging plane
• C. Along the lateral direction
• D. Across the transmitting beam

Answer: (B)

The concept here is slice thickness. Elevational resolution refers to how well two structures that are stacked out of the imaging plane can be distinguished. That ability is governed by how thick the ultrasound beam is in the direction perpendicular to the imaging plane—the elevational direction. A thinner beam in this direction creates a thinner slice, which improves elevational resolution.

Axial resolution depends on the pulse length and wavelength along the beam path. Lateral resolution is determined by the beam width within the imaging plane, side to side. The option describing the beam width perpendicular to the imaging plane best captures elevational resolution, since that width defines the slice thickness.