If you increase the number of transmit focal zones, you typically achieve improved what at the expense of what?

• A. Improved lateral resolution at the expense of frame rate
• B. Decreased lateral resolution at the expense of depth penetration
• C. Improved axial resolution at the expense of dynamic range
• D. Enhanced contrast at the expense of frame rate

Answer: (A)

Placing more transmit focal zones sharpens the beam laterally across the image, improving lateral resolution because the beam is focused at multiple depths to produce narrower slices. However, adding focal zones requires more transmit events per line, which takes more time to acquire a full frame and lowers the frame rate. This is the trade‑off: better lateral detail at the expense of how quickly the image refreshes.

Other aspects aren’t directly affected by changing the number of focal zones in the same way. Axial resolution depends on pulse length and bandwidth, not on focusing along the beam; depth penetration and dynamic range are not governed by how many focal zones you use, and contrast is influenced by factors beyond this focusing approach.