Spatial resolution consists of:

• A. Contrast and temporal resolution
• B. Temporal and axial resolution
• C. Axial and contrast resolution
• D. Lateral and axial resolution

Answer: (D)

Spatial resolution is about distinguishing two structures in space within the image, and it has two parts: axial resolution (along the direction of the beam) and lateral resolution (across the beam). Temporal resolution and contrast resolution are different concepts: temporal resolution relates to how quickly frames are acquired (frame rate) and affects motion portrayal, while contrast resolution concerns the ability to differentiate tissues by brightness. So the two components that define spatial resolution are axial and lateral resolution. Axial resolution is improved with shorter pulse lengths (higher frequency, fewer cycles), which enhances separation of interfaces along the beam. Lateral resolution improves with a narrower beam and good focusing (often via multi-element arrays and proper focusing), which enhances separation across the beam.