Reducing the number of focal zones during scanning primarily affects which imaging parameter?

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

Answer: (A)

Focal zones are the depths where the ultrasound beam is focused to sharpen lateral detail. When you use many focal zones, the system has to perform extra focusing steps at multiple depths for each line of data, which takes more time and lowers the frame rate. Reducing the number of focal zones cuts those extra steps, so frames are acquired faster and temporal resolution improves. Lateral resolution does improve where you have focusing, and using more focal zones extends that improvement across depths, but the trade-off is a slower frame rate. Axial resolution depends on pulse length and bandwidth, not how many focal zones you use, and contrast resolution relates to the system’s ability to distinguish echo amplitudes, which isn’t directly set by the number of focal zones.