In duplex ultrasonography, Doppler flow data are combined with B-mode, or brightness-mode, grayscale ultrasound.
B-mode produces a two-dimensional grayscale image of anatomy, such as vessel walls, valves, and surrounding tissue. Doppler processing adds information about moving blood, including its direction and velocity. Combining the two lets an examiner connect a flow measurement with the exact structure producing it.
The name “duplex” reflects the traditional pairing of structural B-mode imaging with Doppler information. In modern systems, color Doppler may be overlaid on the grayscale image, while spectral Doppler can display a waveform representing velocity over time. Some descriptions call this fuller combination “triplex” imaging because it includes B-mode, color Doppler, and spectral Doppler.
The distractors refer to other ultrasound display modes or nonstandard choices in this context. M-mode is chiefly used to track motion along a single scan line, especially in echocardiography; A-mode displays echo amplitudes rather than a grayscale anatomical image.