Using multiple transmit foci in ultrasound imaging affects which two aspects of resolution?

• A. Temporal resolution and axial resolution
• B. Lateral resolution improves at the expense of temporal resolution
• C. Lateral resolution worsens and temporal improves
• D. Color Doppler frame rate increases

Answer: (B)

Focusing the transmit beam with multiple focal points primarily changes how finely the beam can distinguish objects side-to-side. By having several focal points, the beam stays narrower laterally over depth, yielding better lateral resolution. The trade-off is frame rate: each additional focal point requires extra transmissions to build a complete image line, so the time to acquire a frame increases and temporal resolution decreases. Axial resolution, set by wavelength and pulse length, isn’t significantly altered by adding focal points, and Color Doppler frame rate isn’t improved by this approach. So, using multiple transmit foci improves lateral resolution at the expense of temporal resolution.