Power Doppler and Artifcats

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Power Doppler and Artifcats
2011-09-18 22:19:37
Power Doppler artifacts

Power Doppler
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  1. Power Doppler
    • Does not show direction of flow
    • also known as color power/energy mode
    • the strength of teh reflected signal is processed
    • strength is also known as amplitude
    • The signal is processed without regard to the blood's direction or speed
    • The brightness is directly related to the number of moving blood cells
  2. PDI Transmit Frequency
    As in color Doppler, changing the transmit Doppler frequency in PDI can have a dramatic effect on the receiced signal
  3. Power Doppler Advantages
    • Improved sensitivity to low flow or slow velocity
    • Unaffected by Doppler angles
    • No aliasing since velocity info is ignored
  4. Power Doppler Disadvantages
    • Very slow frame rate
    • Lower temporal resolutions (susceptible to motion of transducer, patient or soft tissue, flash artifact)
    • No flow direction
    • No velocity measurement
  5. Aliasing
    • Doppler sampling rate is too low in comparison to measured blood velocity
    • Aliasing occurs when the doppler shift frequency exceeds haf the PRF
    • This is called the Nyquist Limit
  6. How to correct Aliasing
    • Lower transmit frequency
    • Adjust scale to its maximum (adjusting teh scale will adjust the PRF)
    • Select a lower frequency transducer (doppler shift directly related to transmit frequency)
    • Repostion the transducer so teh area of interest is shallower (this increases the PRF)
    • Adjust the baseline
  7. Mirror Image or Ghosting
    • Duplicates a structure on the other side of a strong reflector
    • Common around the diaphragm and the pleura because of the total reflection from the air-filled lung
  8. Ghosting or Flash
    • Occurs in color doppler
    • Anything within the field of view that moves relative to the transducer is shown in color (generate blotches of color that can obscure a large portion of the field of view)
    • Correct by (increasing wall filter, decreasing persistence, reducing the width of the color box
  9. Color Blossoming of Bleed
    • It is the extension of color beyond the region of flow ot the adjacent tissue
    • Eliminate color bleed by decreasing the color gain or transmit power
  10. Color Noise or Clutter
    • Random variation in signal detection causes area w/o flow to be encoded with color
    • Increase filter or threshold to eliminate he low level echoes
  11. Color Bruit: Visible
    • Useful flow phenomenon
    • A mixture of color is seen withing the soft tissue adjacent to the blood vessel as a result of the vessel wall vibration (it is a valuable marker of vascular pathology, teh wall vibration is an indication of a severe flow disturbance)
    • Can be seen in AV fistulae, arterial stenosis, and pseudoaneurysms
  12. Spectral Doppler Bruit
    • A small strong signal prominent above and below the baseline
    • Occurs in systole