Using multiple transmit focal zones on a linear array primarily improves which aspect of resolution?

• A. Increased lateral resolution
• B. Increased frame rate
• C. Increased axial resolution
• D. Increased contrast resolution

Answer: (A)

Focusing in the lateral dimension is what changes when you use multiple transmit focal zones. By transmitting beams that are focused at several depths, the ultrasound beam is narrower at each focal depth. Narrower beamwidth means better ability to distinguish structures that lie side by side across the image, so lateral resolution is improved over a broader depth range as the system combines the information from those multiple focal zones.

This approach does trade off frame rate (temporal resolution) because more pulses per scan line are needed to cover all focal zones. Axial resolution, which depends on pulse length and frequency, isn’t primarily improved by adding several focal zones. Contrast resolution, tied to signal-to-noise and image processing, isn’t the main gain from multiple focal zones either.

So, the main benefit is improved lateral resolution.