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Vascular Lab > Vascular Lab > Flashcards

Vascular Lab Flashcards

1
Q

What is the Doppler Effect?

A

A change in frequency caused by moving objects.

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2
Q

What are the two components of Sonography?

A

1) Sending pulsees of ultrasound into the body.

2) Using echoes recived from the anatomy to produce an image.

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3
Q

What are ultraound gray-scale scans?

A

pulse-echo images of tisssue cross-sections

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4
Q

Brightness of an echo represents what?

A

stength of the echo

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5
Q

A linear scan is composed of what?

A

many parralel scans

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6
Q

A sector scan is composed of many scan lines with what in common?

A

their origin

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7
Q

What shape is a linear scan?

A

rectangular

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8
Q

A sector scan has what shape?

A

a slice of pie

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9
Q

What shapes can the top of a sector scan have?

A

pointed or curved

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10
Q

Sonography is accomplished by what technique?

A

Pulse-echo

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11
Q

Transducers send what and receive what?

A

U/S pulses and echoes

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12
Q

What re the three displays of Doppler information?

A

Strip-chart recording, spectral display, color display

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13
Q

Sounds is a traveling variation of what?

A

Acoustic variables

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14
Q

What are acoustic variables (3)?

A

Pressure, density, and particle motion

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15
Q

What terms are used to describe all waves? (6)

A 
frequency
period
wavelenght
propagation speed
amplitude
intensity
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16
Q

What is frequency?

A

the number of cycles in a wave that occur in 1 second (Hz)

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17
Q

As sound travels, what are regions of low pressure and high pressure called?

A

rarefaction, compression

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18
Q

What frequency does ultrasound have?

A

> 20, 000Hz

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19
Q

what is a hertz?

A

One cycle per second

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20
Q

What is a period?

A

the time it takes fro one cylce to occur

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21
Q

How does period relate to frequency (equation)?

A

P=1/F

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22
Q

what is Wavelength?

A

length of space over which a cycle occurs

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23
Q

What is propagation speed?

What is the order of propagation speed (gas, solid, liquid)?

A

speed with which a wave moves through a medium

gas, liquid, solid(highest)

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24
Q

how are wavelength, propagation speed, and frequency related (equation)?

A

Wavelength = propagation speed/frequency

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25
Q

Propagation speed are determined by what characteristics of the medium?

A

Density which is the concentration of matter

Hardness which is the resistance of the material to compression

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26
Q

What medium has higher propagation speeds, solid or gas?

A

solid

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27
Q

What is non-linear propagation of a sound wave?

A

when higher pressure portions of the wave travel faster and lower pressure travel slower. This gives the wave a saw-tooth shape.

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28
Q

How many frequencies does a sinusoidal waveform have? a sawtoothed waveform?

A

one, multiple

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29
Q

What is the first frequency and subsequentfrequencies of a saw-toothed waveform called?

A

Fundamental, harmonics

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30
Q

What is the difference is CW US and Pulsed US

A

CW, US cycles repeat indefinitely

PW, pulses seperated by gaps in time. one pulse is a few cycles of US

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31
Q

When is Pulsed US used?

A

Sonography and most of Doppler US

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32
Q

What additional terms describe pulsed U/S over CW?

A 
pulse-repitition frequency,
pulse-repitition period
pulse duration
duty factor
spatial pulse length
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33
Q

what is pulse repetition frequency (PRF)?

A

Number of pulses occurring in 1 second

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34
Q

what is pulse repetition period (PRP)?

A

time to the beginning of the next

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35
Q

When PRF increases what does PRP do?

A

Decreases

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36
Q

What is pulse duration?

A

the time that it takes for one pulse to occur

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37
Q

How many pulses for sonographic vs Doppler pulses

A

2-3, 5-20

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38
Q

How is pulse duration related to the period?

A

PD= period x # of cycles in the pulse (microsecs)

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39
Q

If frequency is increased what happens to the period?

A

decreases

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40
Q

If # of cycles in a pulse is reduced what happens to pulse duration?

A

it decreases

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41
Q

What give better sonographic images shorter or longer pulses?

A

Shorter pulses

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42
Q

What is Duty Factor?

A

the fraction of time that pulsed U/S is on (ie it is not on all the time so it is not 100%)

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43
Q

How is duty factor related to the pulse duration and pulse repetition period?

A

DF= PD/PRP

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44
Q

Duty factors for sonographics U/S vs Doppler?

A

0.1-1%, 0.5-5%

45
Q

What is spatial pulse length?

A

the distance from the begining to the end of a pulse

46
Q

What is amplitude?

A

the maximum variation that occurs in an acoustic variable

47
Q

What is intensity?

A

The rate at which energy passes through a unit of area

48
Q

What is the equation for intensity?

A

I=power/area (cm2)

49
Q

What is power?

A

the rate at which energy is trasnferred

50
Q

Is intensity constant across a sound beam?

A

no it highest in the center and falls of in the periphery

51
Q

What happens to intensity in pulsed U/S

A

some value during the pulse and zero in between

52
Q

Is intensity constant within pulses?

A

starts out high then decreases towards the end of the pulse

53
Q

What is attenuation

A

The weakening of sound as it propogates

54
Q

What are the consequences of attenuation? (2)

A

limits imaging depth, and we must compensate for attenuation with our imaging instrument

55
Q

What causes attenuation?

A

As the sound beam travels amplitude and intensity will decrease. Sound is absorbed as it travels and sound scatters and is reflected off of tissue interfaces and heterogeneous tissue.

56
Q

What units quantify attenuation?

A

decibels

57
Q

What is the attenuation coefficient?

A

Attenuation that occurs with each centimeter the sound wave travles

58
Q

As frequency increases what does attenuation do?

A

increases

59
Q

as frequency increases what does penetration do?

A

decreases

60
Q

In practice what kind of frequency is used for deeper penetration?

A

lower frequencies

61
Q

What is the reflection and scattering of sounds waves at organ and tissue interface called?

A

Echoes

62
Q

What is perpendicular incidence?

A

incident sound either reflect back the direction it came from or continues in the same direction (often both occur). the wave that continues is perpendicular incidence

63
Q

What value is impedance measured in?

A

rayls

64
Q

What is impedance?

A

relationship between acoustic pressure and the speed of particle vibrations in a sound wave.

65
Q

What is the equation for impedance?

A

imp = density x propagation speed

66
Q

What is intensity reflection coefficient? intensity transmission coefficient?

A

divide the echo intensity by the incident intensity and you get the intensity that is reflected (IRC)
divide the transmitted intensity by the incident intensity and you get the intensity that is transmitted to the second medium (ITC)

67
Q

What is the incidence angle?

A

it is the angle measured from a line perpendicular to the surface used when the U/S is at an oblique incidence

68
Q

For oblique incidence what happens to the reflected sound waves (reflection angle)?

A

they are reflected away from the transducer

69
Q

What is refraction?

A

the change of direction of sound when crossing a boudary

70
Q

what is transmission angle?

A

the angle away from a line perpendicular to the surface that the sound wave is travelling through the tissue

71
Q

if propagation speeds are equal, what happens to the incidence angle and the transmission angle?
If propagation speed is greater in the second medium?
if the propagation speed is less in the second medium?
in which scenarios is there refraction?

A

the angle are equal
the transmission angle is greater
the transmission angle is less
the last two, if speed are equal there is no refraction

72
Q

What is scattering?

A

redirection of sound in many directions by a heterogeneous object

73
Q

Why is the U/S display a dot pattern?

A

it is displaying the interference pattern of the scatter distribution scanned

74
Q

why do solids have higher propagation speed then liquids?

A

they have greater stiffness

75
Q

What are odd harmonics of 2MHz?

EVEN?

A

6, 10, 14

4, 8, 12

76
Q

If wavelength is 0.154 mm (over 1micros/sec) what is the propagation speed?

A

WL= propagation speed/time

1.54mm/microsec

77
Q

The number of pulses occurring in one second is called what?

A

pulsed repetition frequency

78
Q

What is the fraction of time the pulsed US is actually on for called?

A

Duty Factor

79
Q

pulse duration = number of cycles in the pulse x what?

A

the period

80
Q

the duty factor of CW doppler is what?

A

1 (100%)

81
Q

What can be calculated if you have propagation speed and frequency?

A

wavelength

82
Q

Which has higher propagation speed, higher or lower stiffness?

A

Higher

83
Q

What is the first harmonic of 3 MHz?

A

6

84
Q

If wavelength is 2 and the frequency is doubled, what does the wavelength become?

A

1

85
Q

If propagation speed is doubled and frequency held constant, what happens to the wavelength?

A

It is doubled

86
Q

What does non-linear propagation mean? (2)

A

depends on the pressure

waveform chages shape as it travels (saw-tooth)

87
Q

If density is 100okg/m and propagation speed is 1540 m/s what is the impedence?

A

1540000 rayls

88
Q

How many cycles are there in 1 second of CW 5 MHz US?

A

5000000

89
Q

What is the unit for intensity?

A

W/cm2

90
Q

Intensity is proportional to what value squared?

A

amplitude

91
Q

If area is doubled and the power remains unchanged, what happens to intensity?

A

halved

92
Q

If power is doubled and area remains unchanged what happens to intensity?

A

Double

93
Q

If both power and area are doubled, what happens to intensity?

A

unchanged

94
Q

If amplitude is doubled what happens to intensity?

A

quadrupled

95
Q

If power is 10mW and bean area is 2 cm2, what is the spatial average intensity?

A

5mW/cm2

96
Q

Multiplying pulse average intensity by duty factor yields what kind of intensity?

A

temporal average intensity

97
Q

Which of the following are equal for CW

spatial peak, spatial average, temporal peak, temporal average

A

temporal peak and average

98
Q

If duty factor 0.5 and pulse average intensity is 4 mW/cm2 what is the temporal average intensity?

A

2

99
Q

attenuation is the reduction of what 2 factors?

A

intensity and amplitude

100
Q

for soft tissue the attenuation per cm for each MHz of requency is what?

A

0.5

101
Q

For soft tissue the attenuation coefficient at 3MHz is approximately what?

A

1.5 dB/cm

102
Q

What does attenuation do in soft tissue when frequency increases?

A

increases

103
Q

Absorption converts sound to what?

A

heat

104
Q

Can absorption be greater then attenuation?

A

no attenuation includes asorption

105
Q

Is attenuation higher in bone or soft tissue?

A

bone

106
Q

What is the attenuation coefficient for soft tissue at 10MHz?

A

5 dB/cm

107
Q

What is the attenuation coefficient for soft tissue at 10MHz?

A

2.5 db/cm

108
Q

What does image depth (penetration) do when frequency increases?

A

decreases

109
Q

If the intensity of a 4 MHz U/S entering soft tissue is 2 W/cm2, what is the intensity at 4cm?

A

0.32 W/cm2 (attenuation is 8dB and intensity ratio is 0.16)

Vascular Lab (5 decks)

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