In color Doppler displays, which color convention is commonly used to represent flow toward the transducer, and how is direction encoded in spectral Doppler?

• A. Toward is red; spectral Doppler uses positive/negative velocity relative to baseline to indicate direction.
• B. Toward is blue; spectral Doppler uses positive/negative velocity relative to baseline to indicate direction.
• C. Toward is red; spectral Doppler uses only speed with no direction indicator.
• D. Toward is blue; spectral Doppler uses only magnitude.

Answer: (A)

In color Doppler, direction and speed are conveyed by color, with toward the transducer most commonly shown as red and away as blue. This helps you quickly gauge not only how fast the flow is moving but also its direction relative to the probe. In spectral Doppler, direction is encoded by the sign of the Doppler velocity relative to a zero baseline. Velocities plotted above the baseline (positive) indicate flow toward the transducer, while velocities below (negative) indicate flow away, and the magnitude shows the speed. This combination lets you read both how fast the blood is moving and in which direction, using the same Doppler principle.