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Vascular 2 > Module 3 : Principles Of Color And Spectral Doppler > Flashcards

Module 3 : Principles Of Color And Spectral Doppler Flashcards

1
Q

Who first described the Doppler effect/ Doppler shift

A
  • Christian johann Doppler
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2
Q

What was the Doppler guy studying when he discovered the Doppler principle

A
  • he was studying the varying color of the stars to determine if they were moving toward or away from the earth
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3
Q

What is the Doppler effect

A
  • change in frequency of sound, light, or other waves caused by the motion of the source or the observer
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4
Q

Ultrasound Doppler shift is caused by what

A
  • change in frequency of sound caused by the motion of red blood cells
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5
Q

The Doppler shift is the difference between what two frequencies

A
  • difference between the transmitted frequency and the received frequency
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6
Q

What is the transmitted frequency

A
  • transducer frequency
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7
Q

What is the received frequency

A
  • reflected or echo frequency
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8
Q

Frequency shift when the RBCs move toward the transducer

A
  • the echo frequency will be larger/higher than the transducer frequency (antegrade flow)
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9
Q

Frequency when the RBCs are moving away from the transducer

A
  • the echo frequency will be smaller/lower than the transducer frequency (retrograde flow)
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10
Q

What is beat frequency

A
  • method used to measure the Doppler shift is based on wave interference
  • the reflected wave will vary slightly from the original transmitted wave the algebraic sum give off beat frequency
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11
Q

In which part of the vessel are cells moving the fastest

A
  • the cells at the center of the vessel move the fastest while those at the sides move the slowest
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12
Q

How is a spectral trace created with the beat frequency

A
  • there are many different frequencies within the beat frequency due to the different velocities of RBCs that are plotted on a graph to form spectral trace
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13
Q

Complicated Doppler shift equation

A

^F = 2Fo x V x Cos0 / C

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14
Q

^ F

A

Doppler shift

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15
Q

Fo

A

Transducer operating frequency

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16
Q

V

A
  • velocity if moving RBCs
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17
Q

Cos0

A
  • angle of insonation
18
Q

C

A
  • speed of sound through soft tissue
19
Q

What is the Nyquist limit

A
  • upper limit to the Doppler shift that can be detected by pulsed instruments
  • 1/2 PRF
20
Q

What must be exceeded if aliasing occurs

A
  • the nyquist limit hast to be exceeded
21
Q

Why does aliasing occur

A
  • PRF is too slow for the true Doppler shift and is sampling the flow to late so its only capturing parts of it
22
Q

Aliasing on color Doppler

A
  • color wraps around the color bar showing both colors with no separation
23
Q

5 ways to compensate for aliasing

A
  • move the baseline
  • increase PRF (scale)
  • increase Doppler angle (not good)
  • lower the operating frequency
  • change to CW
24
Q

What is high PRF mode

A
  • allows the machine to send out subsequent scan lines before the first is returned
25
Q

High PRF mode can lead to what downfall

A
  • range ambiguity
26
Q

What is range ambiguity

A
  • machine does not know what depth the echoes are being returned and could show misrepresented echoes on the display
27
Q

3 ways Doppler info can be represented

A
  • spectral
  • color
  • sound
28
Q

Characteristics of spectral Doppler

A
  • graphed information shown on display

- QUANTITATIVE (can measure speed) using FFT

29
Q

What is fast Fourier transformation (FFT)

A
  • means if taking complex beat frequency and dissecting it into its component waves
  • each wave is the result of a reflection off a moving blood cell within the sample volume
30
Q

Color Doppler characteristics

A
  • visualize flow by sending out two set of scan lines (one for 2D one for color)
  • Doppler info is OVERLAID the 2D
  • obtained using autocorrelation
  • qualitative
31
Q

What velocity does color Doppler represent

A
  • mean flow velocity

- different colors represent positive or negative Doppler shift and give the direction of flow

32
Q

Characteristics of Doppler sound

A
  • Doppler info can be heard

- helps us detect changes in flow

33
Q

Characteristics of CW

A
  • sounds waves emitted continuously from ONE crystal and is continuously received by another crystal
  • zone of sensitivity
34
Q

What is the zone of sensitivity

A
  • in CW the velocities received come from a large overlap zone
  • area where transmitted and received sound is overlapped
35
Q

Advantages to CW

A
  • no nyquist limit so can scan really high velocity with no aliasing
36
Q

Disadvantages to CW

A
  • no range resolution

- no 2D image

37
Q

PW characteristics

A
  • one crystal is used to fire and then listens for returning echoes
38
Q

Advantage to PW

A
  • we know how fast the sound is traveling so we can determine at what depth we would like to sample
39
Q

PW sample volume increase in size causes what

A
  • increases ring time

- increases spectral broadening

40
Q

PW sample size decrease in size does what

A
  • decreases ring time

- samples a more discrete area of flow and the spectral waveform displays less spectral broadening

41
Q

Power Doppler characteristics

A
  • overlay of color onto the 2D image
  • power Doppler uses amplitude of returning Doppler signals to detect flow
  • very sensitive to low flow states and independent of angle
  • directional power Doppler has been introduced

Vascular 2 (9 decks)

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