Power Doppler brightness is related to the number of what?

• A. White blood cells
• B. Plasma molecules
• C. Platelets
• D. Red blood cells

Answer: (D)

Power Doppler brightness reflects the density of moving scatterers in the tissue, primarily the red blood cells in the blood flow. The Doppler energy detected by this mode increases as more red blood cells pass through the sample volume, so brighter signal means more RBCs are present and moving. White blood cells, plasma molecules, or platelets are much less abundant or effective scatterers for this purpose, so they don’t drive the brightness in the same way. Power Doppler emphasizes how much blood is moving rather than how fast it moves, which is why the concentration of red blood cells is the key factor.