Which of the following has the greatest influence on temporal resolution?

• A. Propagation speed and imaging depth
• B. Wavelength of sound and propagation speed
• C. Frequency of sound and propagation speed
• D. Output power and frequency

Answer: (A)

Temporal resolution is controlled by how fast you can acquire consecutive frames, which depends on the time it takes for a pulse to travel to a reflector and back. That round-trip time is determined by the imaging depth and the speed of sound in the tissue: t ≈ 2 × depth / speed of sound. Because depth directly lengthens the travel time and the speed of sound sets the time scale, this combination has the strongest influence on how quickly frames can be captured. If you image deeper, the return signal arrives later and frame rate drops, reducing temporal resolution.

Wavelength and frequency mainly affect how finely structures are resolved along the axis (spatial resolution) and tissue penetration, not how quickly frames are acquired. Output power changes brightness but not the timing of data acquisition.