Using multiple transmit focal zones primarily improves which resolution?

Using multiple transmit focal zones primarily improves which resolution?

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

Answer: (C)

Focusing the ultrasound beam at multiple depths narrows the beam width across a range of depths. Lateral resolution is how well you can distinguish two reflectors that lie side by side, which depends on how narrow the beam is in the sideways direction. By using several transmit focal zones, the beam is compact at each target depth, so two closely spaced objects in the lateral direction are more easily separated across the image. Axial resolution relies on the pulse length and wavelength along the beam, not on where you focus, so it doesn’t gain from multiple focal zones. Elevation resolution concerns the slice thickness in the dimension perpendicular to the imaging plane; multizone focusing mainly tightens the beam laterally rather than elevationally. A practical trade-off is that more focal zones mean more transmit events, which can lower frame rate and temporal resolution.

Focusing the ultrasound beam at multiple depths narrows the beam width across a range of depths. Lateral resolution is how well you can distinguish two reflectors that lie side by side, which depends on how narrow the beam is in the sideways direction. By using several transmit focal zones, the beam is compact at each target depth, so two closely spaced objects in the lateral direction are more easily separated across the image.

Axial resolution relies on the pulse length and wavelength along the beam, not on where you focus, so it doesn’t gain from multiple focal zones. Elevation resolution concerns the slice thickness in the dimension perpendicular to the imaging plane; multizone focusing mainly tightens the beam laterally rather than elevationally. A practical trade-off is that more focal zones mean more transmit events, which can lower frame rate and temporal resolution.