What is the advantage of using multiple transmit focal zones?

• A. Increased lateral resolution
• B. Increased temporal resolution
• C. Increased axial resolution
• D. Increased elevation resolution

Answer: (A)

Using several transmit focal zones tightens the beam at multiple depths, which directly improves how well you can distinguish structures side-to-side. Lateral resolution depends on beam width: a narrower beam yields sharper detail across the image. A single focus is optimized at one depth, so lateral detail is best only there and worsens away from that depth. By transmitting with multiple foci, the beam is narrow at several depths, giving better lateral resolution over a broader range.

Keep in mind the trade-off: more focal zones mean more transmissions per image line, which lowers temporal (frame) rate. Axial resolution and elevational resolution aren’t directly gained by adding focal zones, since axial resolution hinges on pulse length and elevational resolution on beam thickness.