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DMSO Physics 2 > Doppler > Flashcards

Flashcards in Doppler Deck (67):
1

Doppler Shift (Doppler Frequency)

The change or variation in the freq of sound as a result of motion between the sound source and the receiver

2

What is the difference between received and transmitted frequencies?

Doppler shift

3

When reflected frequency is higher than transmitted?

positive change

4

reflected freq is less than transmitted?

negative change

5

Doppler measures _____ not _______

frequency shift, not amplitude

velocity, not speed

6

untis of freq

Hz

7

Typical audible values created when sound reflects off of RBC's

20Hz-20 kHz

8

flow towards the transducers?

increased freq

9

flow away from the transducers

decreased frequencies

10

frequency shift is related to what?

velocity

11

2 MHz-10 MHz transducers are usedto preform doppler ultrasound studies, but doppler shift ranges from?

20Hz-20kHz

12

The process of extracting the Doppler freq (low) form the transducer frequency (high)?

demodulation

13

Doppler shift=

received freq - transmitted freq

14

doppler equation

doppler shift= 2xrefelctor speedxincident frequencyxcos angle/ prop speed

15

Doppler shift is directly related to:

RBC speed, frequency of transducer, cos of angle between flow and sound beam

16

Doppler shift is inversely related to:

speed of sound in the medium

17

velocity (measured)=

true velocityxcos angle

18

Non-choerent processing used with what

uni-directional doppler

19

ultrasound system that displays real-time images and Doppler simultaneously is called?

duplex

20

Phase quadrature processing used in?

bidirectional doppler

21

number of cyrstals in a CW doppler

2

22

Advantage of CW doppler

Able to measure very high velocities

23

Disadvantage of CW Doppler

range ambiguity

24

Echoes arise from entire length of overlap between the transmit and receive beams

range ambiguity

25

how manycrystals are needed for PW Doppler

1

26

Advantage of PW Doppler

Echoes only arise from the area of integration, ample volume or gate.  We adjust the receive gate. Range resolution

27

Disadvantage of PW doppler

Aliasing, errors in measuring high velocities

28

High velocity measurements are inaccurate if the pulsed Doppler sampling rate is too low in comparison to measured blood velocity?

Aliasing

29

What should be done to improve the ability to measure the max velocity with Doppler?

Eliminate aliasing

30

The doppler freq at which aliasing occurs

Nyquist limit (nyquist freq)

31

PRF/2

Nyquist limit (kHz)

32

Aliasing is more likely to occur with higher or lower frquencies?

Higher

33

Five ways to eliminate aliasing

  1. adjust scale
  2. select transducers with low freq
  3. select new view with shallower sample volume
  4. use CW doppler
  5. baseline shift

34

PRF and Nyquist limit are lower with shallower or deeper sample volumes?

deeper

35

______ sampler volumes (gates) create Doppler spectra with larger, cleaner envelopes

smaller

36

Larger sample volumes create doppler sepectra with smaller envelopes known as what?

Spectral broadening

37

The horizontial axis of a doppler spectrum is?

time

38

The vertical axis of a Doppler spectrum is?

doppler shift or velocity

39

relationship between transducer frequency and doppler shift

when freq is halved, doppler shift is half

40

Gray shades on a Doppler spectrum are related to:

Amplitude of the reflected signal or the number of RBC's creating the reflection

41

pulsed doppler

  1. Min of one crystal
  2. range resolution
  3. limit on max velocity
  4. damped, low Q, wide bandwidth

42

Continuous Doppler

  1. min of two crystals
  2. range ambiguity, region of overlap
  3. unlimited max velocity
  4. undamped, high Q, narrow bandwidth

43

imaging transducers

  1. normal incidence
  2. higher freq- improved resolution
  3. pulsed wave only
  4. at least 1 crystal

44

Doppler transducers

  1. 0 to 180 degrees
  2. lower freq
  3. pulsed or CW
  4. 1 (PW) or 2 (CW) crystals

45

color doppler reports

average velocities

46

variance mode

color map that varies side to side.   left side: laminar   right side: turbulent

47

Which setting has the greatest effect on jet size?

Color doppler gain

48

Multiple ultrasound pulses are needed to accurately determine RBC velocities by doppler?

A packet or ensemble length

49

Advantages of more pulses in the packet

greater accuracy of the velocity measurement sensitivity to low flow

50

disadvantages of more pulses in the packet?

More time is required to acquire info

frame rate is reduced

temporal resolution is decreased

51

Why does color doppler measure mean velocity?

the packet size must balance between accurate velocity measurements and temporal resolution

52

Synonyms for power doppler

energy mode or color angio

53

Advantages of power doppler

  1. increased sensitivity to low flow
  2. not effected by doppler angle unless 90 degrees
  3. no aliasing

54

limitations of power doppler

  1. no measurement of velocity
  2. slower frame rates
  3. susceptible to motion (flash artifact)

55

performed to extract or identify the individual freq making up a complex signal?

spectral analysis

56

Spectral analysis method for pulsed or CW doppler

Fast Fourier transform

57

spectral analysis for color flow doppler

autocorrelation or correlation function

58

FFT and autocorrelation are what type of techniques

digital

59

used due to the large amount of Doppler information that requires processing?

Autocorrelation

Slightly less accurate, but faster than FFT

60

Can a successful Doppler exam be preformed regardless of a patients hematocrit?

yes

61

Ghosting

Low velocity motion from pulsating vessel walls can also produce small doppler shifts that bleed into surrounding anatomy

62

High pass filter

Eliminates low magnitude Doppler shifts that are created from moving anatomy rather than red blood cells

63

Wall filters are used to reject?

Clutter

64

color flash is also called?

ghosting

65

Cross talk is in?

doppler only

66

Special form of mirror image where the Doppler spectrum appears above and below the baseline?

Cross talk

67

Cause of crosstalk

Doppler gain set too high

Incident angle near 90 degrees when flow is at focus