Doppler ultrasonography

Doppler ultrasonography

(Doppler ultrasound, Doppler sonography, Doppler test or Doppler study) is a non-invasive procedure that uses detectable changes in high frequency sound waves (2-20 MHz), based on the Doppler effect, to create clear digital images in real time. As a medical imagery method, it is used for diagnostics, during medical procedures or for pathology research. It has been in general use for several decades in medicine with no or little report of long-term side effects. Thus, characterized as harmless, painless, cost-effective and generally widely available (note: also requires little or no prior patients preparation or aftercare). Predominantly, it is used to monitor the circulatory system by detecting direction, velocity and turbulence of blood flow, in order to provide information on possible blood clots, blocked vessels, cardiac or valve insufficiency.

Physical principles Doppler ultrasonography is based on two basic principles:
 * 1) Ultrasound principle
 * high-frequency sound wave aimed at a target will be reflected back and detected
 * 1) Doppler principle
 * effect of changes in the sound pitch depending on the movement of the object in relation to the observer (positive or negative shift)

Piezoelectric crystals within the transducer or probe produce electrical pulses when vibrated by the returning wave. The transducer will send a thousands of series of waves, which may be continuous or pulsed. If pulsed then pauses for detection of the returning pulses are necessary. Upon detection, ultrasonograph calculates and determines the direction and depth of each returning sound wave. These are displayed as pixels on the screen. Thousands of such pulses sent and detected are computed and displayed in order to produce an image of the studied object. Also the use of color helps in depicting direction and rate of blood flow clearly for the physician interpreting the results (note: as there is no standard on what color will depict which effect or type of vessel, this varies between manufactures or operating modes).

Gel

Angles

Types color flow Doppler ultrasound a form of pulse wave Doppler in which the energy of the returning echoes is displayed as an assigned color; by convention echoes representing flow towards the transducer are seen as shades of red, and those representing flow away from the transducer are seen as shades of blue. The color display is usually superimposed on the B-mode image, thus allowing simultaneous visualization of anatomy and flow dynamics. continuous wave Doppler ultrasound a technique in which the transducer emits and receives the ultrasound beam continuously, enabling the measurement of high velocity blood flow, such as occurs through heart valve stenoses. color flow Doppler ultrasound a form of pulse wave Doppler in which the energy of the returning echoes is displayed as an assigned color; by convention echoes representing flow towards the transducer are seen as shades of red, and those representing flow away from the transducer are seen as shades of blue. The color display is usually superimposed on the B-mode image, thus allowing simultaneous visualization of anatomy and flow dynamics. continuous wave Doppler ultrasound a technique in which the transducer emits and receives the ultrasound beam continuously, enabling the measurement of high velocity blood flow, such as occurs through heart valve stenoses. duplex Doppler ultrasound a form of image display in which both spectral and color flow images are seen simultaneously. This facilitates accurate anatomical location of the blood flow under investigation. Doppler ultrasound flowmeter a device for measuring blood flow that transmits sound at a frequency of several megahertz downstream along the flowing blood. Some of the sound waves are reflected by the moving red blood cells back toward the transducer. The difference in pitch between the transmitted and reflected sounds is produced as an audible tone and is proportional to the velocity of blood flow. The flowmeter can be incorporated into a stethoscope so that qualitative and quantitative measurements of the flow of blood through arteries and veins can be obtained. The Doppler flowmeter is capable of recording very rapid pulsatile changes in flow as well as steady flow. pulse wave Doppler ultrasound a technique in which the transducer emits ultrasound in pulses. Blood flow velocities so measured are limited to around the physiologic range (up to approximately 1.5 meters/second) but the depth from which the returning echoes originate can be accurately determined. spectral Doppler ultrasound a form of ultrasound image display in which the spectrum of flow velocities is represented graphically on the Y-axis and time on the X-axis; both pulse wave and continuous wave Doppler are displayed in this way.

a form of image display in which both spectral and color flow images are seen simultaneously. This facilitates accurate anatomical location of the blood flow under investigation. Doppler ultrasound flowmeter a device for measuring blood flow that transmits sound at a frequency of several megahertz downstream along the flowing blood. Some of the sound waves are reflected by the moving red blood cells back toward the transducer. The difference in pitch between the transmitted and reflected sounds is produced as an audible tone and is proportional to the velocity of blood flow. The flowmeter can be incorporated into a stethoscope so that qualitative and quantitative measurements of the flow of blood through arteries and veins can be obtained. The Doppler flowmeter is capable of recording very rapid pulsatile changes in flow as well as steady flow. pulse wave Doppler ultrasound a technique in which the transducer emits ultrasound in pulses. Blood flow velocities so measured are limited to around the physiologic range (up to approximately 1.5 meters/second) but the depth from which the returning echoes originate can be accurately determined. spectral Doppler ultrasound a form of ultrasound image display in which the spectrum of flow velocities is represented graphically on the Y-axis and time on the X-axis; both pulse wave and continuous wave Doppler are displayed in this way.

Disrupted or obstructed blood flow through the neck arteries may indicate the person is a risk of having a stroke. (Narrowed arterial flow in the legs does not necessarily indicate a risk of stroke.)