Color Doppler Ultrasound: Red, Blue, and White Color Interpretation
In Doppler ultrasound, red and blue colors indicate the direction of blood flow relative to the ultrasound probe—NOT arterial versus venous blood—while white (or bright colors) indicates high-velocity flow. 1
Color Assignment Based on Flow Direction
- Red colors (including orange and yellow) represent blood flow moving TOWARD the ultrasound transducer, regardless of whether the vessel is an artery or vein 1, 2
- Blue colors (including cyan) represent blood flow moving AWAY FROM the ultrasound transducer 1, 2
- The color assignment depends solely on flow direction relative to the probe position, not on vessel type—this is the most common misinterpretation to avoid 1
White and Bright Colors: Velocity Information
- Brighter or lighter shades of red and blue indicate faster blood flow velocities, while darker shades indicate slower flow 1
- White or yellow colors (aliasing) appear when blood flow velocity exceeds the machine's measurement capacity (exceeds the Nyquist limit) 1
- This aliasing creates a multicolored mosaic pattern and should not be misinterpreted as pathology—it simply indicates high-velocity flow and can be normal in certain vessels 1
Power Doppler Distinction
- Power Doppler displays flow amplitude (strength) as a single color (usually orange or yellow) rather than showing directional information 1
- Power Doppler is more sensitive for detecting slow flow and flow in small vessels compared to color Doppler 1, 3
- The trade-off is that power Doppler provides no directional information about blood flow 1
Clinical Applications
- Color Doppler helps differentiate true vascular flow from solid components such as clots, debris, or hemorrhagic material within masses 3, 1
- Internal vascularity detected by color Doppler helps distinguish malignancy from benign solid-appearing components 3
- A color score ranging from 1 to 4 (no flow to very strong flow) is used in standardized classification systems like O-RADS for adnexal mass characterization 3, 1
Critical Pitfalls to Avoid
- Never interpret red as arterial and blue as venous—this is the most common error in Doppler interpretation 1, 2
- Absence of color flow does not always mean absence of vascularity—slow flow may be below the detection threshold, and technical factors like gain settings significantly affect visualization 1
- Distinguish true flow from motion artifacts by using spectral Doppler to confirm actual blood flow versus movement-related color changes 1, 3
- Flow perpendicular to the ultrasound beam may not be detected, while 0-degree angles provide optimal velocity measurements 1