Doppler and Hemodynamics

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dorkfork
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288414
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Doppler and Hemodynamics
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2014-11-06 18:52:09
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Ultrasound Physics hemodynamics sonography spi doppler
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Ultrasound physics hemodynamic and doppler reveiw
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  1. Flow through a blood vessel is determined by:
    • 1. Pressure difference
    • 2. Vascular resistance
  2. Vessel diameter increase as _____ increases.
    Pressure
  3. Veins or arteries, which are more distensible?
    Veins are 6-10 x as distensible as arteries
  4. Arteries
    • Transport blood to tissues
    • High pressure
  5. Arterioles
    • Last, smallest branches of the arterial system
    • Act as "control valves" for blood flow into capillaries
  6. Capillaries
    Exchange between blood and interstital spaces
  7. Vasodilitation occurs when?
    • During exercise
    • After a meal
  8. Vasoconstriction occurs when?
    • In a resting state
    • With fasting
  9. Venules
    Collect blood from capillaries and connect to larger veins
  10. Veins
    • Blood returned to heart
    • Body contians many more veins than all other parts of the vascular system
  11. AO/ICV
    Have the smallest cross-section area and therefore the highest velocity
  12. Relationship of velocity to area
    Velocity is inverse to area
  13. Energy derived from the cardiac pump
    Potential/pressure energy
  14. Potential energy
    • Pressure/stored energy
    • Derived from the cardiac pump
    • Distends vessels and stores energy
  15. Kinetic energy
    • Energy of motion
    • KE < PE due to distensibility of vessels
  16. Kinetic energy can increase due to:
    • Increase in flow>> i.e. exercise
    • Stenosis (increased velocity)
  17. Movement of fluid between 2 points requires:
    • Difference in energy
    • Difference in pressure
  18. Example of low resistance
    • Organs
    • Low resistance = greater energy difference = greater flow
  19. Example of high resistance
    • Resting muscle
    • High resistance = less flow
  20. Pouseuille's law
    Defines relationship between pressure, volume flow, and resistance
  21. The longer the vessel the _____ the resistance.
    • Higher
    • High pressure is required to maintain flow
  22. The shorter the vessel the ____ the flow volume.
    Higher
  23. What has the most significant impact on flow rate?
    • Radius of the vessel
    • Smaller the radius, the higher the resistance
  24. Smaller the radius, the _____ the resistance.
    Higher (and higher pressure)
  25. Plug flow
    • Flat profile
    • Seen in stenotic area
    • Same velocity throughout vessel (slower flow at wall)
  26. Laminar flow
    • Most common flow pattern
    • Seen during systole in smaller arteries
    • Flow in center is highest and gradually tapers as it reaches the wall of the vessel
  27. Disturbed flow is signified by?
    Spectral broadening
  28. Mathematical number to determine when flow turbulence will occur?
    Reynold's number
  29. Reynolds number for when turbulance will occur
    2000 Re or higher
  30. Harmonic resonance produced by flow turbulence transmitted into vessel walls is known as
    audible bruit
  31. Where is normal disturbed flow visualized throughout the cardiac cycle?
    • Bifurcations
    • Curves
  32. Significant stenosis
    70% blockage
  33. Tardus parvus
    Dampened wave forn distal to a stenosis
  34. Monophasic flow
    • Low resistance, continuous and steady throughout S and D
    • Seen in normal arteries that supply low resistance vascular beds -liver, spleen, brain, kidneys
  35. Triphasic flow
    • Highest resistance to flow
    • Antegrade/forward flow during systole
    • Retrograde/reverse flow during diastole
    • Seen in distal AO/iliac arteries
  36. Cosine of the doppler angle is ______ly related to the doppler angle.
    • Inversely related
    • Angle of 0 = cosine 1.00
    • Angle of 90 = cosine 0
  37. Increase transmit frequency and _____ the size of the Doppler shift
    Increase
  38. Decrease velocity of flow and _____ the size of the Doppler shift.
    Decrease
  39. Increase the Doppler angle and _____ the size of the Doppler shift.
    Decrease
  40. Decrease the Doppler angle and ______ the size of the Doppler shift.
    Increase
  41. Cosine = 0
    • 90 degree angle
    • No Doppler shift
  42. Cosine = 1.00
    • 0 degree angle
    • Largest Doppler shift
  43. With spectral analysis the frequency is displayed on which axis?
    Vertical y axis
  44. What is displayed on the X axis of spectral analysis?
    Time
  45. Amplitude or power is displayed as what on spectral analysis?
    Brightness
  46. FFT
    • Fast fourier time
    • Current computer program for analyzing and displaying spectral representation
  47. How can aliasing be eliminated?
    • Increase PRF (increased nyquist limit)
    • Shift baseline
    • Increase size of angle
    • Decrease transmit frequency
  48. Main disadvantage of pulsed Doppler is?
    Aliasing
  49. Nyquist Limit
    • 1/2 the PRF
    • Exceeding this produces aliasing
  50. PRF control
    Changed the number of pulsed emitted per second
  51. Primary advantage of CW Doppler
    No velocity limit/ no aliasing
  52. Main disadvantage of CW Doppler
    • Large fixed sample volume
    • POOR RANGE RESOLUTION
  53. Color Doppler
    • Qualitative, NOT quantitative information
    • Will produce aliasing
    • Good range resolution
    • BART
  54. How to eliminate color aliasing
    • Increase PRF (scale setting)
    • Decrease sample volume depth
    • Use larger Doppler angle
    • Lower transmit frequency
    • Go from triplex(color, image, spectra) to duplex (color, image)
  55. Power Doppler
    • Encodes amplitude of blood cells
    • Provides no info on direction of flow
    • NO aliasing and less angle dependant
  56. Components of pulsed Doppler instrumentation:
    • Pulser
    • Gated detector
    • Spectral analysis
    • Memory
    • Display
    • Speakers
  57. Length of pulses produced by pulser
    5-30 cycles
  58. The time period for acquisition of Doppler signal is determined by the _____.
    Size of the gate
  59. Phase shift means
    Motion is present
  60. Rhythmic cycles or beats produced when waves of different frequencies produce interference are added together and termed
    Beat frequency
  61. Minimum number of cycles per pulse is?
    4
  62. Number of cycles required for fast flow
    6-10
  63. Number of cycles needed for gray scale
    2-3 cycles
  64. Number of cycles needed for slow flow
    20-30
  65. Typical sampling rate
    25,600 times per second
  66. High pass filter
    • Rejects all frequencies below the threshold vaule
    • Usually 100Hz
    • Removes wall thump but not slow flow
  67. Low pass filter
    • Eliminates high frequency noise
    • Improper adjustment can eliminate high frequency (fast) flow
  68. One speed estimate has a _____  pulse minimum.
    Three
  69. More than 3 pulses are required in order to:
    • Improve accuracy of the estimate
    • Determine the variance
    • Improve detection of slow flow
  70. Typical ensemble length range
    10-20 pulse
  71. Increasing ensemble length will ___ frame rate.
    Decrease
  72. Ensemble length
    • AKA pulse packet size
    • The number of pulses required to produce one color scan line

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