This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals in Radiology, Subject name: Radiology
The intensity of colour in Doppler is determined by - 
Select and explain. 
A. Direction of flow, B. Velocity of flow, C. Strength of returning echo, D. None of the above
B: Velocity of flow
Answer: B: Velocity of flow 
Explanation: Color intenstiy indicates the relative velocity of the red blood cells. yellow white represents the highest velocity for flow directed towards the transducer. green white represents the highest velocity for flow directed away from the transducer. Doppler effect is due to shift in sound frequency as the sound as reflected from the moving Red blood cells.