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Hemodynamic and Doppler > Ch 19 > Flashcards

Ch 19 Flashcards

1
Q

Doppler Shift or Doppler frequency

A

The change in frequency

Used to measure velocity of blood in the circulation

a low frequency that rides on top of a much higher transducer frequency

range from 20 Hz to 20 kHz and are in the audible range

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2
Q

When does the frequency of sound change?

A

when the sound source and the receiver move closer together or father apart

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3
Q

When doesn’t the frequency change?

A

the distance between the sound source and receiver remain constant

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4
Q

Demodulation

A

the process of extracting the low Doppler frequency from the transducer’s carrier frequency

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5
Q

Creation of a frequency shift

A

transmitted sounds waves strike moving red blood cells

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6
Q

Positive Doppler Shift

A

Moves toward transducer

Doppler Shift is positive

Reflected frequency is higher than the transmitted frequency

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7
Q

Negative Doppler Shift

A

Blood cells move away from the transducer

Doppler Shift is negative

Reflected frequency is lower than the transmitted frequency

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8
Q

Speed vs Velocity

Doppler Frequency indicates which

A

Velocity not speed

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9
Q

Speed vs Velocity

Speed

A

magnitude

indicates the distance that a red blood cells moves in 1 sec

cm/s

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10
Q

Speed vs Velocity

Velocity

A

magnitude and direction

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11
Q

Doppler shift equation

A

2 x velocity of blood x transducer frequency x cos / propagation speed

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12
Q

Doppler Shift relations to velocity of blood

A

directly related

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13
Q

First shift during Doppler Shift exam

A

occurs when the sound waves from the transducer strikes moving blood cells

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14
Q

Second shift during Doppler Shift exam

A

after the sound waves strikes blood cells, reflections return to the transducer

results from transducer reception of sound waves from moving blood cells

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15
Q

Doppler Shift relation with frequency of the transmitted sound

A

directly related

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16
Q

Doppler Shift units

A

Hz

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17
Q

Measurement of the Doppler frequency depends on

A

the relationship between the direction of the blood flow and the direction in which the sound waves propagate

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18
Q

Doppler Shifts represents

A

100% of the true velocity when blood flow is parallel to sound beam

could be moving directly to or away from transducer

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19
Q

Doppler shifts when there is an angle

A

Doppler measures something less than the true velocity

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20
Q

Cosine

A

Percentage of the true velocity that is measured depends on the cosine of the angle between the sound beam and the direction of motion

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21
Q

Measured velocity =

A

true velocity x cosine

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22
Q

Doppler Shift relation with the cosine of the angle between the direction of flow and the direction of sound

A

directly related

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23
Q

0 and 180

A

flow is parallel to sound beam and measured velocity are equal

24
Q

Cosine 0

A

flow toward transducer

25
Q

Cosine 180

A

flow away from transducer

26
Q

Perpendicular, 90 degrees

A

measured velocity is zero because cosine of 90 is zero

Doppler can’t be measured

27
Q

Cosine 60 degree is

A

0.5, 1/2 the actual velocity

28
Q

Flow toward the transducer is displayed _____ baseline

A

above

29
Q

Flow toward the transducer is displayed _____ baseline

A

below

30
Q

Phase quadrature, or quadrature detection

A

commonly used signal processing technique for bidirectional Doppler

31
Q

Bidirectional Doppler distinguishes

A

which direction the flow is going

32
Q

Continuous Wave Doppler

A

requires two crystals, one transmits and one receives reflections

33
Q

Continuous Wave Doppler

Advantages

A

ability to accurately measure very high velocities

34
Q

Continuous Wave Doppler

Disadvantages

A

exact location of the moving blood cells can’t be determined

35
Q

Range Ambiguity

A

Signals arise from all blood cells in the region of overlap between the transmitted and receive beam

36
Q

Continuous Wave Doppler

Disadvantages

A

Lack of TGC

located deeper will have a lower amplitude than reflections from blood cells that are at shallower depths

Doppler shifts produced by deeper blood cells may be incorrectly interpreted as having been created by fewer blood cells

37
Q

Duplex Imaging

A

Simultaneous anatomic imaging and Doppler

38
Q

Continuous Wave Transducer

A

A dictated continuous wave does not create anatomic images

39
Q

Continuous Wave Transducer don’t use a backing layer which results in

A

undampened transmitted signal

narrow bandwidth

high quality factor

higher sensitivity

40
Q

Matching layer is used in

A

both duplex and dedicated continuous wave transducer

41
Q

Dedicated Continuous Wave Transducer

A

have increase sensitivity

detect low amplitude reflections and small Doppler shift

42
Q

Pulsed Wave Doppler

A

Only one PZT is necessary

alternate between sending and receiving the sound pulses

43
Q

Pulsed Wave Doppler Advantages:

Range Resolution

A

Able to select the exact location where velocities are measured

range specificity, or freedom form range ambiugity artifact

44
Q

Pulsed Wave Doppler Disadvantages

A

inaccurate measurement of high velocity is signaled

45
Q

Sample volume or gate

A

sonographer positions a small marker on image

then calculated the time of flight for a sound pulse traveling to and from the gate

transducer emits a sound pulse and then waits that time of flight before briefly listening for a reflection

46
Q

Pulsed Wave Transducer

A

Contains backing layer

low quality factor

lower sensitivity

wide bandwidth pulses

47
Q

Aliasing

A

most common error associated with Doppler ultrasound

false identity

Very high velocities in one direction are incorrectly displayed as going in the opposite direction

48
Q

Two ways aliasing is created

A

Pulsed Doppler

Doppler sampling rate is too low in comparison to the measured blood velocity

49
Q

Nyquist limit equation

A

PRF / 2

50
Q

Nyquist frequency or Nyquist limit

A

highest Doppler frequency or velocity that can be measured without the appearance of aliasing

51
Q

Aliasing occurs when

A

Doppler sampling rate is too low in comparison to the measured blood velocities

52
Q

Penalty

A

issued when speed is over the limit

53
Q

Two ways to avoid penalty

A

raise speed limit

reduce the speed

54
Q

Aliasing occur when

A

the Doppler shift exceeds the Nyquist limit

55
Q

Two ways to avoid aliasing

A

raised the Nyquist limit

reduce the Doppler shift

Hemodynamic and Doppler (6 decks)

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