In Doppler imaging, which modality provides high sensitivity to low-velocity flow but does not show directional information?

• A. Power Doppler
• B. Color Doppler
• C. Spectral Doppler
• D. Tissue Doppler

Answer: (A)

Power Doppler detects the strength or energy of the Doppler signal from moving blood, not the actual velocity. By summing the Doppler signal energy within each voxel, it becomes highly sensitive to very slow flow and flow in small vessels. However, because it encodes flow presence as energy rather than velocity, it does not convey direction (toward or away) or exact speed. This contrasts with color Doppler, which shows velocity and direction but is less sensitive to slow flow; spectral Doppler and tissue Doppler provide velocity profiles and directional information (or measure tissue motion, not blood flow). So the modality that emphasizes detecting low-velocity flow without providing direction is Power Doppler.