[Medical Q&A] What is the difference between spectral Doppler ultrasound and color Doppler ultrasound?

Planner: Chinese Medical Association

Reviewer: Wang Yandong, Chief Physician, Tianjin University Central Hospital

Both spectral Doppler ultrasound and color Doppler ultrasound are ultrasound examination technologies based on the Doppler effect (the phenomenon that the frequency of the waves received by the observer changes when the relative position of the wave source and the observer changes). They can be used to evaluate the speed, direction and nature of blood flow, but there are some differences between the two in their working principles, display methods and application scenarios.

From the working principle, although both spectral Doppler and color Doppler are based on the Doppler effect, the former uses quantitative analysis to measure the speed and direction of blood flow by analyzing the changes in ultrasonic frequency, while the latter uses color coding, that is, blood flow in different directions is displayed on the ultrasound image in different colors, usually red represents blood flow toward the probe, and blue represents blood flow away from the probe. From the display method, the results of spectral Doppler are usually displayed as a two-dimensional chart, with the horizontal axis representing time, the vertical axis representing blood flow speed, and positive and negative values ​​representing the direction of blood flow. This method can only provide detailed information of a specific location, while color Doppler superimposes a color blood flow map on the standard B-type ultrasound image, so the blood flow situation in the entire detection area will be clear at a glance. From the perspective of application scenarios, spectral Doppler is suitable for situations where detailed information about the blood flow velocity and direction at a specific location is required (such as arterial stenosis, venous reflux, etc.), while color Doppler is more suitable for simultaneous monitoring of large areas or multiple areas (such as cardiac ultrasound, abdominal organ perfusion, etc.) because it can dynamically observe the overall distribution and flow pattern of blood flow in a larger range. However, it is not as accurate as spectral Doppler in reflecting blood flow velocity information, and can only intuitively show whether blood flow exists and its general direction.