Color assignments can be switched on any ultrasound system and are used as directional indicators. The colors of red and blue indicates flow direction in color Doppler.
Red is encoded to represent flows toward the transducer.
Blue pixel encoding is used to depict flows away from the transducer.

See also Directional Color Power Doppler.

The divergence is an ultrasound beam characteristic of the far field. The beam divergence angle q, depends on the transducer frequency and diameter according to the following approximation:
sin q 1.22 ld
where l is the wavelength of the ultrasound in the medium of propagation and d is the diameter of the transducer element.

Duplex systems often combine a pulsed Doppler with a spectral display and a real time imaging system. A duplex scanner has usually an imaging transducer or a separate transducer used to collect continuous wave or pulsed Doppler signals, either simultaneously with imaging or sequentially.

The duty factor is the product of the pulse duration and the pulse repetition frequency (the lapse of time the transducer is actively transmitting sound).
Most transducers are acting as the receiver 99 % of the time with a duty factor of 1.

See also Dwell Time.

Dynamic focusing controls the axial position of the focus of an ultrasound beam. Dynamic focusing is often managed by controlling the phase of the signals detected by a transducer array.

See also Real-Time Transducer.