Increasing the number of transmit focal zones to improve spatial resolution involves the following tradeoff:

• A. lateral resolution vs. axial resolution
• B. lateral resolution vs. temporal resolution
• C. spatial resolution vs. contrast resolution
• D. contrast resolution vs. frame rate

Answer: (B)

Focusing the transmitted beam more narrowly across depth improves lateral resolution because the beam is steadier and objects side by side are resolved more distinctly at each depth. However, adding more transmit focal zones requires delivering more focused pulses per frame, which takes more time to complete. That extra time lowers the frame rate, reducing temporal resolution—the ability to track rapid changes over time. Axial resolution, on the other hand, is governed mainly by the pulse length and bandwidth, not by how many focal zones you use, so it isn’t the primary tradeoff here. So increasing transmit focal zones gives better lateral detail at the cost of slower frame rate.