In Doppler measurement one counters problem of accuracy, precision and artifacts like in any measurement and imaging method. It is important to clearly differentiate among the tree concept.
Precision
The quantitative functional depended of the velocity measurement error on the knowledge of the angle α is known. However, the usual method of measurement of the angle is very crude and thus one should try to avoid using abuse values whenever possible.
Precision
The quantitative functional depended of the velocity measurement error on the knowledge of the angle α is known. However, the usual method of measurement of the angle is very crude and thus one should try to avoid using abuse values whenever possible.
Accuracy
Doppler spectrometry operates adequately for angles between ultrasound beam and flow less than 600. The theoretical measurement error then symptomatically toward 900. The accuracy of the assessment of the Doppler shift really depend on the knowledge and control of the frequency content of the ultrasound pulses. This often not well controlled. An exception is operation with CW Doppler systems where measurement can be made more accurate.
Color Doppler it self is not designed as an accurate measurement method, but mainly a semi quantitative guiding method for Doppler shift spectroscopy. In spite of this, the significance old different colors must be known and particular one must carefully adjust the base line shift since this can essentially change velocity color map. Power Doppler display method has slightly better geometrical accuracy in showing the blood vessel lumen that the normal color Doppler. This happens at cost of image repetition.
Artifact
Several artifacts are encountered in Doppler ultrasound. these are incorrect presentation of Doppler flow information.. However other occur, including range ambiguity, spectrum mirror image . Location mirror image, speckle and electromagnetic interference.
Aliasing
Aliasing is the most common artifact encounters in Doppler ultrasound. There is an upper limit to Doppler shift that can be detected by pulsed instruments, If the Doppler shift frequency exceed one half the pulse repetitions frequency, aliasing occurs and improper wrong value) results. an analogous optical form of aliasing occurs in motion pictures when wagon wheels appear to rotate in reverse direction. This happens here because the number of pictures per second is insufficient to correctly show the rotation screed. Aliasing can be eliminated by increasing pulse repetition frequency, increasing Doppler angle which decreases the Doppler shift for a given flow) or by baseline shifting. The latter is an electronic "cut and paste" technique as long as there are no legitimate Doppler shifts in region of the aliasing. Other approach to eliminating aliasing include changing to a lower frequency Doppler transducer or chaining to a continuous wave instrument, which is often build in specialized cardiologist unit. Aliasing can occur in a pulse system since it is a sampling system. Which can not yield a correct results unless it samples often enough, that is twice he highest Doppler shift frequency, (Nyqusit limit)
Doppler spectrometry operates adequately for angles between ultrasound beam and flow less than 600. The theoretical measurement error then symptomatically toward 900. The accuracy of the assessment of the Doppler shift really depend on the knowledge and control of the frequency content of the ultrasound pulses. This often not well controlled. An exception is operation with CW Doppler systems where measurement can be made more accurate.
Color Doppler it self is not designed as an accurate measurement method, but mainly a semi quantitative guiding method for Doppler shift spectroscopy. In spite of this, the significance old different colors must be known and particular one must carefully adjust the base line shift since this can essentially change velocity color map. Power Doppler display method has slightly better geometrical accuracy in showing the blood vessel lumen that the normal color Doppler. This happens at cost of image repetition.
Artifact
Several artifacts are encountered in Doppler ultrasound. these are incorrect presentation of Doppler flow information.. However other occur, including range ambiguity, spectrum mirror image . Location mirror image, speckle and electromagnetic interference.
Aliasing
Aliasing is the most common artifact encounters in Doppler ultrasound. There is an upper limit to Doppler shift that can be detected by pulsed instruments, If the Doppler shift frequency exceed one half the pulse repetitions frequency, aliasing occurs and improper wrong value) results. an analogous optical form of aliasing occurs in motion pictures when wagon wheels appear to rotate in reverse direction. This happens here because the number of pictures per second is insufficient to correctly show the rotation screed. Aliasing can be eliminated by increasing pulse repetition frequency, increasing Doppler angle which decreases the Doppler shift for a given flow) or by baseline shifting. The latter is an electronic "cut and paste" technique as long as there are no legitimate Doppler shifts in region of the aliasing. Other approach to eliminating aliasing include changing to a lower frequency Doppler transducer or chaining to a continuous wave instrument, which is often build in specialized cardiologist unit. Aliasing can occur in a pulse system since it is a sampling system. Which can not yield a correct results unless it samples often enough, that is twice he highest Doppler shift frequency, (Nyqusit limit)
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