Which ultrasound technique has the worst temporal resolution?

• A. B-mode
• B. Spectral Doppler
• C. Pulsed-Wave Doppler
• D. Color Doppler

Answer: (D)

Temporal resolution is the frame rate—the number of image updates per second. Higher frame rates mean better ability to track rapid motion. B-mode grayscale imaging is designed for high frame rates because it simply forms a standard image without Doppler data. Doppler techniques add information, but not all add the same amount of data. Spectral and pulsed-wave Doppler sample velocity along a single scan line and generate time-based waveforms; this keeps the data volume more compact and allows relatively quick updates along that line. Color Doppler, on the other hand, overlays velocity information across many pixels of the image, mapping velocities to colors for multiple locations simultaneously. This added processing and data across the entire field reduces the frame rate, giving color Doppler the poorest temporal resolution among the options.