From the Guidelines
In Doppler ultrasound, red typically indicates blood flow moving toward the transducer, while blue indicates blood flow moving away from the transducer. This color coding is based on the Doppler effect, where sound waves reflected from moving objects (like blood cells) change frequency. When blood flows toward the probe, the frequency increases (positive Doppler shift), displayed as red. When blood flows away from the probe, the frequency decreases (negative Doppler shift), displayed as blue. This convention helps clinicians quickly interpret the direction of blood flow in vessels, which is crucial for diagnosing conditions like valve regurgitation, stenosis, or vascular occlusions, as seen in the evaluation of carotid stenosis using Duplex carotid Doppler 1, 2. The intensity of the color typically correlates with the velocity of blood flow, with brighter shades indicating faster flow. It's essential to consider the orientation of the transducer, as it affects the color display, so the same vessel can appear red or blue depending on the angle of the probe relative to blood flow.
Some key points to consider when using Doppler ultrasound include:
- The accuracy of Duplex carotid Doppler in evaluating carotid stenosis, with a 90% sensitivity and 94% specificity in identifying clinically significant stenosis 1, 2
- The importance of caution when evaluating patients with extremely severe stenosis or multivessel involvement, as Doppler can overestimate or underestimate the degree of stenosis 1, 2
- The potential for US imaging to be the only necessary examination in patients with carotid bruit, in the absence of suspected confounding factors or active treatment plans 2
Overall, understanding the color coding in Doppler ultrasound is crucial for accurate interpretation of blood flow and diagnosis of vascular conditions, and should be used in conjunction with other clinical factors to guide patient management.
From the Research
Doppler Ultrasound Significance
- Red or blue colors on Doppler ultrasound signify the direction of blood flow 3
- The choice of color (red or blue) depends on the direction of flow with respect to the ultrasound probe
- Typically, red indicates blood flowing towards the probe, while blue indicates blood flowing away from the probe 3
Technical Aspects
- Doppler ultrasound measures the frequency shift of the ultrasound signal as it interacts with moving blood cells 4
- The frequency shift is proportional to the velocity of the blood cells, but the exact velocity cannot be determined without knowing the angle between the ultrasound beam and the flow velocity vector 4
- Power Doppler ultrasound encodes the power in the Doppler signal in color, providing an image of a different property of blood flow compared to traditional color Doppler 3
Clinical Applications
- Doppler ultrasound is used to diagnose and monitor various vascular conditions, such as deep vein thrombosis and peripheral artery disease 5, 6, 7
- The technique can provide valuable information on blood flow and vessel morphology, helping clinicians make informed decisions about patient management 5, 6, 7