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Flashcards in SPI review 5 Deck (71):
1

flow towards the transducer

increased flow

2

flow away from trans

decreased flow

3

the doppler shift ranges from

20-20000Hz

4

the process by which the doppler freq (shift) is extracted from the trans freq

demodulation
(tran freq high, doppler freq is low)

5

doppler shift = rcvd freq - transmitted freq

FD = FR - FE

6

doppler equation

doppler shift=2xreflector speedxincident freqxcos(angle)/prop speed

7

doppler shift is directly related to the

red blood cell speed

freq of transducer

cosine of the angle between flow and the sound beam

8

doppler shift is inversly related to

the speed of the sound in the medium

9

what does the 2 in the doppler equation represent

double doppler shift, 1st occurs when the sound stikes the cell the 2nd the moving blood cell reflecting the wave back to the transducer

10

in order to accuratley determine velocity

the angle between the directions of flow and sound beam must be known

11

doppler measures velocity not

speed

12

velocity is

magnitude and direction

13

doppler freq depends on direction. The magnirude of shift depends upon the

cosine of the angle between the sound beam and the direction of motion

14

angle is
0
60
90

the cosines are

1
0.5
0

15

doppler shift is inversly related to

the speed of sound in a medium

16

non coherent processing is used with

unidirectioinal dopper

17

a basic doppler system (non or unidirectional dopper) that simply identifies the blood flow by the presence of

a freq shift, it does not distinguish blood flowing towards or away from trans

18

more sophisticated doppler systtem which distinguishes

flow towards and away from trans

19

bidirectional doppler distiguishes to and from trans by

the measurment of positive and negative doppler shifts

20

____ __________ is used in bidirectional doppler

phase quadrature

21

number of crystals in continuous wave trans

two
one is transmitting and one is receiving

22

advantage of continuous wave dopper

able to measure very high velocities accurately

23

disadvantage of continuous wave dopper

range ambiguity-echoes arise from entire length of overlap between the transmit and rcv beams

24

range means

depth

25

other advantages of continuous wave doppler

higher sensitivity and ease in detecting small doppler shifts

26

pulsed wave doppler number of crystals

one crystal that alternates between sending and rcving

27

advantages of pulsed wave doppler

range resolution aka

range specificity

freedom from range ambiguity

echoes arise only from the area o interrogation, the sample volume or gate. we adjust the receive gate

28

disadvantage of pulsed wave doppler

aliasing, errors in measuring high velocities

29

imaging and pulsed doppler can be performed with a single crystal trans. Simultanious imaging and doppler is know as

duplex ultrasound

30

high velocities appear negative. with pulsed doppler, high velocity measurements are inaccurate if the pulsed doppler sampling rate (PRF) is too low in comparison to measured blood velocity

aliasing

31

eliminating aliasing

improves the ability to measure the max velocity with doppler

32

the doppler freq at which aliasing occurs, = to 1/2 the PRF.

nyquist freq

33

nyquist limit (kHz) =

(kHz) = PRF/2

34

deeper samples are more

likely to have aliasing

35

w/ _____ freq transducers, aliasing is more likely to occur

higher

36

5 ways to eliminate aliasing

adjust the scale (increases the PRF and Nyquist limit)

get trans w/ lower freq

get a new window/view with shallower sample volume

switch to continuous wave doppler

adjust baseline(only appears gone)

37

smaller sample volumes (gates) create doppler spectra with ____ _____ ______

larger cleaner envelopes

38

larger sample volumes (gates) create doppler spectra with ____ _____

smaller envelopes (spectral broadening)

39

x axis on doppler spectrum

time

40

y asxis of doppler spectrum is

doppler shift or velocity

41

doppler shift and trans freq are _____ related

directly

42

with a 7MHz probe doppler shift is 3000Hz, what will the shift be with a 3.5MHz probe

1,500Hz

43

gray shades on a doppler spetrum are related to

amplitude of the reflected signal

number of red blood cells creating the reflection

44

color doppler is pulsed ultrasound technique and is subject to

range resolution or specificity

aliasing

45

color doppler is

semi quantitative

46

color doppler reports

average velocities aka mean velocities

47

color doppler gain setting has greatest effect on

jet size

48

doppler packets

multiple pulses are needed to determine RBC celocites by dopplers, single measurement is not enought

49

multiple doppler pulses are call

packet

aka

ensemble length

50

the packet must balance between accurate velocity measurements and

temporal resolutions, this is why color doppler measures mean velocity

51

disadvanage to doppler packets

more time needed

frame rate is reduced

temp res is decreased

52

advantages of doppler packets

greater accuracy

sensitivity to low flows

53

spectral doppler (pulsed and continuious) measures _______ -______ while color flow measures _____ ______

peak velocity

mean velocity

54

color power doppler aka

energy mode and color angio

advantages

increased sensitivity to low flows

not affected by doppler angles unless its 90*

no aliasing

55

color power doppler limitations

no velocity measurement

slower frame rate and temp res

susceptible to motion of trans, patient or soft tissues, called flash artifact

56

spectral analysis

performed to extract or edentify the individual freq making up the complex signal

57

spectral analysis for pulsed or CW doppler

fast fourier transform (FFT)

58

spectral analysis for color flow doppler

autocorrelation or correlation function

59

FFT and autocorrelations are

digital techniques performed by computors

60

autocorrelation is used w color doppler cause of the enormous amount of doppler info that requires processing. It is ____ _____ but ______ than FFT

less accurate

faster

61

anremia and doppler

we can always successfully perform a doppler exam regardless of the patients hematocrit

62

RBC closest to the trans will create the highest

amplitude

63

no dppler shift is measured at a _____ angle

90*

64

at what engle will the doppler shift be at max

0*

65

T or F
only pulsed wave dopppler has ample vomules

T

66

T or F
the higher the emitted freq the more likely the pulsed wave signal is to alias

T

67

pulsed wave doppler has a rcv gate that is

adjusted by sonographer

68

nyquist limit -

1/2 PRF

69

errors in imaging

artifacts

70

artifacts are

not real
missing reflectors
iimproper brightness
improper shape
improper size
improper position

71

causes of artifacts

violation of assumptions (acoustic artifacts)

equipment malfunction or design

physics of ultrasound

interpreter error (anatomic pitfalls)

operator error