Doppler ultrasound
Doppler ultrasound: A form of ultrasound that can detect and measure blood flow. Doppler ultrasound depends on the Doppler effect, a change in the frequency of a wave resulting here from the motion of a reflector, the red blood cell.
There are several kinds of Doppler ultrasound:
Color Doppler — This technique estimates the average velocity of flow within a vessel by color coding the information. The direction of blood flow is assigned the color red or blue, indicating flow toward or away from the ultrasound transducer.
Pulsed Doppler — This method allows a sampling volume or “gate” to be positioned in a vessel visualized on the gray-scale image, and displays a graph of the full range of blood velocities within the gate versus time. The amplitude of the signal is approximately proportional to the number of red blood cells and is indicated, not in color, but simply as a shade of gray.
Power Doppler — This device depicts the amplitude, or power, of Doppler signals rather than the frequency shift. This allows detection of a larger range of Doppler shifts and thus better visualization of small vessels, but at the expense of directional and velocity information.
Color Doppler depicts blood flow in a region and is used as a guide for the placement of the pulsed Doppler gate for more detailed analysis at a particular site.
Doppler ultrasound has many applications including, for example, the detection and measurement of decreased or obstructed blood flow to the legs. Color Doppler ultrasound is done first to evaluate vessels rapidly for abnormalities and to guide placement of the pulsed Doppler to gain sample volume for detailed analysis of velocities.
Named for Christian Johann Doppler (1803-1853), the Austrian physicist, who discovered the effect that now bears his name.
Read Also:
- Doraphobia
Doraphobia: An abnormal and persistent fear of fur. Sufferers of this fear avoid fur-bearing animals such as dogs, cats, foxes, beavers and rabbits because fur is repulsive to them. Perhaps some of these phobics associate fur with childhood stories about “the big bad wolf” and other fur-bearing predators. Their fear is not always unfounded, for […]
- Dorian Gray effect
Dorian Gray effect: Sudden aging, an abrupt change from seeming youthfulness to the reality and ravages of age, as can occur naturally or when the effects of plastic surgery and Botox treatments wear off. Named after “The Picture of Dorian Gray” (1890), the novel by Oscar Wilde, in which Dorian gives his soul to remain […]
- Dormant tuberculosis
Dormant tuberculosis: See: Tuberculosis, dormant. See also: Tuberculous meningitis.
- Dorsal
Dorsal: Relating to the back or posterior of a structure. As opposed to the ventral, or front, of the structure. Some of the dorsal surfaces of the body are the back, buttocks, calves, and the knuckle side of the hand. For a more complete listing of terms used in medicine for spatial orientation, please see […]
- Dorsum
Dorsum: The back or posterior side of a structure. Something that pertains to the dorsum is dorsal.