Focusing improves which aspect of resolution by decreasing beam width?

• A. Axial resolution
• B. Lateral resolution
• C. Temporal resolution
• D. Contrast resolution

Answer: (B)

Focusing narrows the ultrasound beam in the plane across its path, so the cross-sectional footprint becomes smaller at the focal depth. With a narrower beam, two objects that lie side by side in the lateral direction are sampled by a smaller portion of the beam, making it easier to distinguish them as separate structures. This directly boosts lateral resolution, which is the ability to resolve objects side-to-side.

Axial resolution, on the other hand, depends on the spatial length of the emitted pulse (the number of cycles and wavelength) and is not improved by focusing. Temporal resolution relates to how quickly frames are acquired (frame rate), not beam width. Contrast resolution is about distinguishing different tissues based on brightness and is more influenced by signal-to-noise and dynamic range than by beam focusing.