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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
Cosine 180
flow away from transducer
26
Perpendicular, 90 degrees
measured velocity is zero because cosine of 90 is zero Doppler can't be measured
27
Cosine 60 degree is
0.5, 1/2 the actual velocity
28
Flow toward the transducer is displayed _____ baseline
above
29
Flow toward the transducer is displayed _____ baseline
below
30
Phase quadrature, or quadrature detection
commonly used signal processing technique for bidirectional Doppler
31
Bidirectional Doppler distinguishes
which direction the flow is going
32
Continuous Wave Doppler
requires two crystals, one transmits and one receives reflections
33
Continuous Wave Doppler Advantages
ability to accurately measure very high velocities
34
Continuous Wave Doppler Disadvantages
exact location of the moving blood cells can't be determined
35
Range Ambiguity
Signals arise from all blood cells in the region of overlap between the transmitted and receive beam
36
Continuous Wave Doppler Disadvantages
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
Duplex Imaging
Simultaneous anatomic imaging and Doppler
38
Continuous Wave Transducer
A dictated continuous wave does not create anatomic images
39
Continuous Wave Transducer don't use a backing layer which results in
undampened transmitted signal narrow bandwidth high quality factor higher sensitivity
40
Matching layer is used in
both duplex and dedicated continuous wave transducer
41
Dedicated Continuous Wave Transducer
have increase sensitivity detect low amplitude reflections and small Doppler shift
42
Pulsed Wave Doppler
Only one PZT is necessary alternate between sending and receiving the sound pulses
43
Pulsed Wave Doppler Advantages: Range Resolution
Able to select the exact location where velocities are measured range specificity, or freedom form range ambiugity artifact
44
Pulsed Wave Doppler Disadvantages
inaccurate measurement of high velocity is signaled
45
Sample volume or gate
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
Pulsed Wave Transducer
Contains backing layer low quality factor lower sensitivity wide bandwidth pulses
47
Aliasing
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
Two ways aliasing is created
Pulsed Doppler Doppler sampling rate is too low in comparison to the measured blood velocity
49
Nyquist limit equation
PRF / 2
50
Nyquist frequency or Nyquist limit
highest Doppler frequency or velocity that can be measured without the appearance of aliasing
51
Aliasing occurs when
Doppler sampling rate is too low in comparison to the measured blood velocities
52
Penalty
issued when speed is over the limit
53
Two ways to avoid penalty
raise speed limit reduce the speed
54
Aliasing occur when
the Doppler shift exceeds the Nyquist limit
55
Two ways to avoid aliasing
raised the Nyquist limit reduce the Doppler shift

Hemodynamic and Doppler (6 decks)

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