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DMSO Physics 2 > SPI review 5 > Flashcards

SPI review 5 Flashcards

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1
Q

flow towards the transducer

A

increased flow

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2
Q

flow away from trans

A

decreased flow

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3
Q

the doppler shift ranges from

A

20-20000Hz

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4
Q

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

A

demodulation

tran freq high, doppler freq is low

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5
Q

doppler shift = rcvd freq - transmitted freq

A

FD = FR - FE

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6
Q

doppler equation

A

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

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7
Q

doppler shift is directly related to the

A

red blood cell speed

freq of transducer

cosine of the angle between flow and the sound beam

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8
Q

doppler shift is inversly related to

A

the speed of the sound in the medium

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9
Q

what does the 2 in the doppler equation represent

A

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

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10
Q

in order to accuratley determine velocity

A

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

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11
Q

doppler measures velocity not

A

speed

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12
Q

velocity is

A

magnitude and direction

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13
Q

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

A

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

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14
Q

angle is
0
60
90

the cosines are

A

1
0.5
0

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15
Q

doppler shift is inversly related to

A

the speed of sound in a medium

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16
Q

non coherent processing is used with

A

unidirectioinal dopper

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17
Q

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

A

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

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18
Q

more sophisticated doppler systtem which distinguishes

A

flow towards and away from trans

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19
Q

bidirectional doppler distiguishes to and from trans by

A

the measurment of positive and negative doppler shifts

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20
Q

____ __________ is used in bidirectional doppler

A

phase quadrature

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21
Q

number of crystals in continuous wave trans

A

two

one is transmitting and one is receiving

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22
Q

advantage of continuous wave dopper

A

able to measure very high velocities accurately

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23
Q

disadvantage of continuous wave dopper

A

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

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24
Q

range means

A

depth

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25
Q

other advantages of continuous wave doppler

A

higher sensitivity and ease in detecting small doppler shifts

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26
Q

pulsed wave doppler number of crystals

A

one crystal that alternates between sending and rcving

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27
Q

advantages of pulsed wave doppler

A

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

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28
Q

disadvantage of pulsed wave doppler

A

aliasing, errors in measuring high velocities

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29
Q

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

A

duplex ultrasound

30
Q

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

A

aliasing

31
Q

eliminating aliasing

A

improves the ability to measure the max velocity with doppler

32
Q

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

A

nyquist freq

33
Q

nyquist limit (kHz) =

A

(kHz) = PRF/2

34
Q

deeper samples are more

A

likely to have aliasing

35
Q

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

A

higher

36
Q

5 ways to eliminate aliasing

A

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
Q

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

A

larger cleaner envelopes

38
Q

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

A

smaller envelopes (spectral broadening)

39
Q

x axis on doppler spectrum

A

time

40
Q

y asxis of doppler spectrum is

A

doppler shift or velocity

41
Q

doppler shift and trans freq are _____ related

A

directly

42
Q

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

A

1,500Hz

43
Q

gray shades on a doppler spetrum are related to

A

amplitude of the reflected signal

number of red blood cells creating the reflection

44
Q

color doppler is pulsed ultrasound technique and is subject to

A

range resolution or specificity

aliasing

45
Q

color doppler is

A

semi quantitative

46
Q

color doppler reports

A

average velocities aka mean velocities

47
Q

color doppler gain setting has greatest effect on

A

jet size

48
Q

doppler packets

A

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

49
Q

multiple doppler pulses are call

A

packet

aka

ensemble length

50
Q

the packet must balance between accurate velocity measurements and

A

temporal resolutions, this is why color doppler measures mean velocity

51
Q

disadvanage to doppler packets

A

more time needed

frame rate is reduced

temp res is decreased

52
Q

advantages of doppler packets

A

greater accuracy

sensitivity to low flows

53
Q

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

A

peak velocity

mean velocity

54
Q

color power doppler aka

energy mode and color angio

advantages

A

increased sensitivity to low flows

not affected by doppler angles unless its 90*

no aliasing

55
Q

color power doppler limitations

A

no velocity measurement

slower frame rate and temp res

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

56
Q

spectral analysis

A

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

57
Q

spectral analysis for pulsed or CW doppler

A

fast fourier transform (FFT)

58
Q

spectral analysis for color flow doppler

A

autocorrelation or correlation function

59
Q

FFT and autocorrelations are

A

digital techniques performed by computors

60
Q

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

A

less accurate

faster

61
Q

anremia and doppler

A

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

62
Q

RBC closest to the trans will create the highest

A

amplitude

63
Q

no dppler shift is measured at a _____ angle

A

90*

64
Q

at what engle will the doppler shift be at max

A

0*

65
Q

T or F

only pulsed wave dopppler has ample vomules

A

T

66
Q

T or F

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

A

T

67
Q

pulsed wave doppler has a rcv gate that is

A

adjusted by sonographer

68
Q

nyquist limit -

A

1/2 PRF

69
Q

errors in imaging

A

artifacts

70
Q

artifacts are

A 
not real
missing reflectors
iimproper brightness
improper shape
improper size
improper position
71
Q

causes of artifacts

A

violation of assumptions (acoustic artifacts)

equipment malfunction or design

physics of ultrasound

interpreter error (anatomic pitfalls)

operator error

DMSO Physics 2 (26 decks)

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