Triplex exam means the use of three ultrasound modalities in a single examination to study blood flow with gray scale imaging, color Doppler and spectral Doppler.

(CD) Color Doppler is an ultrasound imaging mode, which visualizes the presence, direction and velocity of flowing blood in a wide range of flow conditions. It provides an estimate of the mean velocity of flow within a vessel by color coding the flow and displaying it superimposed on the 2D gray scale image. The flow direction is arbitrarily assigned the color red or blue, indicating flow toward or away from the transducer.
Color (colour, Brit.) Doppler ultrasound is capable of evaluating a wider area than other Doppler modes than for example Duplex or power Doppler, and therefore makes it less likely to miss flow abnormalities. It is also easier to interpret. Color flow is not as precise as conventional Doppler and is best used to scan a larger area and then use conventional Doppler for detailed analysis at a site of potential flow abnormality.

Adjustments for color Doppler in case of too much color:
Adjustments for color Doppler in case of not enough color:
See also Color Power Doppler, Autocorrelation, Color Priority, Triplex Exam and Color Saturation.

Gray scale [also grayscale, grey scale = brit.] produces basically black and white images with series of shades of gray. Solid areas appear white and fluid areas appear black, varying from black at the weakest intensity to white at the strongest. Gray scale resolves artifacts as small as 1 mm. The display is made by transmitting bursts of energy and analyzing the returning signal. Gray scale pictures are limited to the gray scale tones; color pictures display more information because the color is added to the gray scale.
Most ultrasound contrast agents also improve gray scale visualization of the flowing blood to such a degree that the tissue echogenicity increases. Gray scale enhancement of flow in an organ promises to improve lesion detection, along with the ability to differentiate between normal and abnormal areas, using many of the criteria already routinely used in CT and MRI.

See also Compress, Densitometry, Triplex Exam and QB-Mode.

Spectral Doppler refers to the combination of either continuous wave Doppler or pulsed Doppler with a spectral display. Spectral Doppler provides a quantitative analysis of the velocity and direction of blood flow.
The Fourier spectrum analyzer performs a fast Fourier transformation on the Doppler signal. The amplitudes of the resulting spectra are encoded as brightness. In the 2D spectral display, the frequency shift is depicted in the vertical and the time in the horizontal axis. The range of blood velocities in the volume produces a corresponding range of frequency shifts.

See also Acceleration Index and Triplex Exam.