Which measurement is used to assess lateral resolution in a phantom?

• A. Depth axis
• B. Lateral width of a target
• C. Elevational width
• D. Temporal resolution

Answer: (B)

Lateral resolution is about how well two features that sit side by side in the image (across the width of the image) can be distinguished. In a phantom, this is quantified by looking at how wide a target must appear along the lateral (left–right) direction to be resolved. Measuring the lateral width of a target gives a direct read on how finely the system can separate side-by-side structures; a smaller measured width means better lateral resolution because the system can distinguish thinner features along the lateral axis.

The other measurements relate to different aspects: depth axis corresponds to axial resolution, which is the ability to separate targets along the beam’s travel direction; elevational width pertains to the dimension across the elevational plane (thickness in that dimension); temporal resolution deals with how quickly frames are acquired (frame rate), not with the spatial separation of targets.