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SPI > Doppler > Flashcards

Doppler Flashcards

1
Q

Relative motion between the sound source and the receiver. The change in frequency is due to

A

Doppler shift / doppler frequency

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2
Q

Doppler frequency is used to measure the

A

velocity

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3
Q

Process the extracts the low doppler frequency from the transducers carrier frequency

A

demodulation

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4
Q

Doppler shift formula

A

Doppler shift (hz) = reflected frequency - transmitted frequency

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5
Q

When blood cells move toward the transducer it creates a ____ and the reflective frequency is ___ than transmitted

A

positive doppler shift / higher

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6
Q

Doppler shifts are created when ___ sound waves strike moving red blood cells

A

transmitted

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7
Q

Doppler shifts range from ___ to ___ whereas transducer frequencies range from ____ to _____

A

20 to 20,000 hz / 2 mhz to 10 mhz

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8
Q

Velocity is defined by

A

magnitude and direction

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9
Q

doppler shift equation

A

Doppler shift = 2 x velocity x transducer frequency x cos / prop speed

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10
Q

Relationship between velocity and doppler shift

A

directly / the faster the velocity, the greater the doppler frequency

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11
Q

the x axis of a doppler spectrum represents ___ and the y axis represents ___

A

time / doppler shift (velocity)

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12
Q

requires 2 crystals in the transducer

A

CW doppler

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13
Q

The greatest advantage of CW doppler is

A

ability to accurately measure very high velocities

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14
Q

Disadvantages of CW doppler

A

range ambiguity and lack of TGCs

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15
Q

Transducer that does not create anatomic images and contains only 2 elements

A

CW transducer

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16
Q

Since CW transducers do not have damping material, what are the characteristics

A

narrow bandwidth, high Q factor, and high sensitivity

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17
Q

The crystal alternates between sending and receiving sound pulses so only 1 put crystal is needed.

A

PW doppler

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18
Q

The greatest advantage of PW doppler is

A

being bale to select the exact location where velocities are measured (range resolution)

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19
Q

In PW doppler, the velocities are measured from the

A

sample volume (gate)

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20
Q

The most common error associated with PW doppler is

A

aliasing

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21
Q

High velocity flow in one direction is incorrectly displayed as traveling in the opposite direction

A

Aliasing

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22
Q

Since PW transducer have backing material, what are the characteristics

A

wide bandwidth, low sensitivity, low Q factor

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23
Q

The very top of the baseline is called the

A

Nyquist limit

24
Q

Aliasing occurs when the doppler sampling rate is ___ in comparison to the measured blood velocities

A

too low

25
Q

The highest doppler frequency/velocity that can be measured without the appearance of aliasing

A

Nyquist frequency (limit)

26
Q

Nyquist limit formula

A

Nyquist limit (hz) = PFR/ 2

27
Q

2 ways to avoid aliasing are

A

raise the nyquist limit and reduce the doppler shift

28
Q

___ frequency transducers create more aliasing

A

higher

29
Q

5 techniques to avoid aliasing

A

Increase PRF
Select a shallower sample volume
lower frequency transducer
use baseline shift
use CW doppler

30
Q

Range resolution, sample volume, nyquist limit, and aliasing (what doppler)

A

PW doppler

31
Q

Range ambiguity, region of overlap, unlimited max velocity, no aliasing

A

CW doppler

32
Q

PW transducer characteristics (5)

A

1 crystal
dampened pzt
low Q factor
Wide bandwidth
low sensitivity

33
Q

CW transducer characteristic (5)

A

2 crystals
undampened pzt
high Q factor
narrow bandwidth
high sensitivity

34
Q

Higher frequency, pw only, 1 crystal, and normal incidence

A

Imaging

35
Q

0 or 180 agrees, low frequency, pulsed or cw, 1 or 2 crystals

A

Doppler

36
Q

Color doppler measures

A

mean velocity

37
Q

Spectral doppler measures

A

peak velocity

38
Q

Provides information regarding direction of flow. It is a pulsed ultrasound technique.

A

Color flow doppler

39
Q

Color flow doppler has range ___

A

resolution (range specificity)

40
Q

The 2 most commonly use dictionaries for color maps are

A

Velocity and variance mode

41
Q

The black region in the middle of the color map represents

A

No doppler shift

42
Q

This mode provides information on flow direction and velocity

A

Velocity mode

43
Q

With velocity mode maps, the color change is always

A

up and down

44
Q

This mode distinguishes laminar flow from turbulent flow

A

Variance mode

45
Q

Colors on the left side of the map represent

A

laminar flow

46
Q

With variance mode, the color change

A

side to side and up - down

47
Q

Non directional color doppler and only identifies the presence of a doppler shift

A

Power doppler

48
Q

Power doppler is also called

A

energy mode or color angio

49
Q

Used to eliminate low frequency doppler shifts from moving anatomy. Serve as a reject

A

Wall filter

50
Q

Wall filters are also called

A

high pass filters

51
Q

Special form of mirror image artifact arising only from spectral doppler.

A

Cross talk

52
Q

Crosstalk results from

A

doppler gain is too high
The incident angle is near 90 degrees between the flow direction and the sound beam

53
Q

Tool that breaks the complex signal into its basic building blocks and identifies the individual velocities that make up the reflected doppler signal

A

Spectral analysis

54
Q

A digital technique used to process both pulsed and cw doppler signals. that distinguishes laminar flow from turbulent flow

A

Fast Fourier transform (FFT)

55
Q

Used to analyze color flow doppler. Less accurate but faster than fast Fourier transforms

A

Autocorrelation

56
Q
A

SPI (16 decks)

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