How does dynamic focusing affect lateral resolution?

• A. It continuously adjusts focus to maintain a narrow beam width over a range of depths.
• B. It increases the transmit power.
• C. It reduces the frame rate.
• D. It fixes a single focal depth.

Answer: (A)

Dynamic focusing sharpens the beam width across multiple depths. By adjusting the timing of the transmitted wavefronts (and/or during reception), the system keeps the focal region effectively narrow as the depth changes. Since lateral resolution depends on beam width in the perpendicular direction, maintaining a narrow beam over a range of depths means objects that are side-by-side can be distinguished over a larger portion of the image. If you fixed the focus at one depth, the beam would be narrow only there and would broaden elsewhere, reducing lateral resolution away from that focal point. Increasing transmit power changes penetration or signal strength but not how narrow the beam is. Using several focal zones can slightly reduce frame rate because more transmissions are needed, but the key effect on lateral resolution comes from keeping the beam narrowly focused across depths.