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Instrumentation 2 > Sonography 1 + 2 > Flashcards

Sonography 1 + 2 Flashcards

1
Q

What is a ultrasound?

A

Sound waves of frequencies higher than the range of
human hearing and their movement (propagation) in a
medium

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2
Q

What is converted into a grey scale value in US?

A

The echo amplitude.

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3
Q

What is compression?

A

increase of density during propagation

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4
Q

What is rarefaction

A

decrease of density during propagation

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5
Q

Does sound move along the waveform?

A

no

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6
Q

What is a complete cycle?

A

compression followed by a rarefaction

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7
Q

How many cycles in pulsed US?

A

2-5

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8
Q

What frequency does diagnostic US travel at?

A

-2 MHz to 20 MHz

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9
Q

Is a high frequency attenuated more or less?

A

more.

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10
Q

Which frequencies have the higher spatial res?

A

High frequencies

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11
Q

Best frequencies for deep tissues and why?

A

Low because high frequencies will be attenuated before they can hit the structure.

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12
Q

What is wavelegnth?

A

the physical length of the cycle

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13
Q

What is period? (t)

A

Length of time it takes for a cycle to start and finish.

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14
Q

What is the strength of the US beam?

A

its amplitude.

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15
Q

What is the velocity of propagation?

A

Speed of which US travels..

CONSTANT FOR A SPECIFIC TISSUE

1540 ms-1

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16
Q

What is the speed of sound in soft tissue?

A

1540 m/s

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17
Q

Which has a faster speed of sound: air or bone?

A

bone

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18
Q

What is acoustic impedance?

A

 A measure of the resistance of a medium to the transmission of sound.
 The product of velocity (c) of the medium and the density (p) of the medium
 The acoustic impedance is a constant for each medium.

measured in rayls

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19
Q

If there is an increased acoustic impedance BETWEEN materials, will there be less or more reflection?

A

more

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20
Q

What do we spend 99.9% of the time in US doing?

A

listening for echoes.

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21
Q

can a transceiver emit and receive a pulse SIMULATEANOUSLY?

A

no

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22
Q

How long does the reflection from a depth of 1cm take in soft tissue?

A

13micro seconds

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23
Q

What is PRF max?

A

maximum pulse repition frequency

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24
Q

What is PRF max limited by?

A

Imaging depth.

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25
Q

at a larger depth what has to happen for the PRF

A

Less pulses per second due to longer listening times

INCREASED IMAGING DISTANCE = DECREASED PRF.

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26
Q

What is PRS

A

Pulse repetition period :

The time between the start of one pulse to the start of the
next pulse.
 The time required to transmit a pulsed ultrasound wave plus the time devoted to listening for the returning echoes from that wave

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27
Q

If PRS increases what happens to PRF max?

A

Decreases

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28
Q

What is SPL and what does it determine?

A

spatial pulse length.

This is like wavelength .. it is a physical length measurement and hence affects Axial resolution

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29
Q

What is PD?

A

pulse duration

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30
Q

If SPL increases what happens to PD

A

also increases

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31
Q

If SPL increase what happens to axial resolution?

A

decreases

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32
Q

What is Duty factor?

A 
Measure of the fraction of time that the transducer is
emitting sound (or is active).
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33
Q

What is axial resolution?

A

Resolution along the axis of the beam.

THe smaller the resoltuon the better…

in US it should be 1 mm or better.

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34
Q

Does a longer or shorter pulse length give a better axial resoltuon?

A

Shorter is better as its not travelling as far.. so higher frequencies will be attenuated less.

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35
Q

Which beam width increases lateral resolution: wide or narrow?

A

Narrow.

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36
Q

Generally which is better in US? axial or lateral resolution?

A

Axial as the US beam is usually shorter than it is wider.

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37
Q

What is attenuation?

A

Reduction of intensity as sound propagates through a medium

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38
Q

Will an echo reflected at the surface of the body be stronger or weaker than an echo reflecting from an identical structure, deep within the body?

A

Stronger

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39
Q

What affects attenuation in US?

A

Tissue density and shape

Distance travelled

Frequency of the beam

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40
Q

What is the approximate rate of attenuation in soft tissue?

A

1dB/MHz/cm

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41
Q

What is a positive dB value?

A

When a wave has a higher intensity than the reference

wave. AMPLIFIED THE SIGNAL

42
Q

What does doubling and halving the intensity do to the dB?

A

Doubling : +3 dB

Halving : -3dB

43
Q

Why is dB used?

A

compresses large attenuation values into a simpler scale to use.

44
Q

What is the reference wave in US?

A

The intensity produced by the transeiver.

45
Q

What dB values do we expect in US?

A

negative

46
Q

What does a higher frequency have on attenuation

A

More attenuation

47
Q

what are the 4 types of US interactions with a medium?

A

Reflection

Refraction

Scattering

Absorption

48
Q

Which US interaction produces heat?

A

Absorption… can be used in US therapy to help create bloodflow.

49
Q

Which US interaction produces artefacts?

A

Refraction

50
Q

Is US absorption useful for image quality?

A

No. it doesn’t contribute to the image at all.

but the heat can be used for US therapy.

51
Q

Why is absorption more common in higher frequencies?

A

Because higher frequencies are absorbed more.

52
Q

Which tissues absorb more sound?

A

denser structures such as bone.

53
Q

Where does reflection occur?

A

at large SMOOTH surfaces like diaphragm and organ boundaries.

54
Q

Why do we aim to get the US beam to hit the structure at 90 degrees?

A

So it reflects back at that angle.

55
Q

What is angle of incident equal to?

A

angle of reflection

56
Q

Is reflection related to the frequency of the wave or changes in acoustic impedance?

A

it is NOT related to frequency..

it is an attenuation element and thus related to acoustic impedance.

57
Q

Why is gel and drinking water used in US?

A

to decrease the large differences in acoustic impedance.. so some sound can transmit and not hit a wall.

58
Q

WHy is scatter important in US?

A

shows the ‘texture’ of a surface and shows internal structures of organs.

59
Q

WHat is scattering dependent on?

A

Frequency… a higher frequency will increase scattering.

60
Q

When is scatter really useful?

A

Doppler or moving objects.

61
Q

Why is there more scattering in surface imaging?

A

BEcause higher frequencies are used during surface imaging

62
Q

Why does refraction occur?

A

Only occurs if the velocity of sound is different in the two media and when angle of incidence is not perpendicular.

Tissue one density is differnt to tissue 2.

63
Q

If the velocity of speed of sound is lower in the second medium… will it bend towards or away from the ‘normal’

A

towards.

64
Q

If there is larger differences between two mediums what will happen?

A

larger angle of refraction

65
Q

If the refracted beam has bended AWAY from the normal, what has occured?

A

The velocity of the speed of sound in the second medium is higher so the angle has INCREASED.

66
Q

Which effect is used to generate US?

A

CONVERSE piezoelectrict effect.

Electrical energy -> mechanical energy.

67
Q

WHat is the piezoelectric effect?

A

When the echo returns and mechanical energy is converted into electric energy.

68
Q

What is the material in PZT?

A

lead zirconium titanate

69
Q

What do materials need to contain for piezoelectric effect to occur?

A

Dipoles

70
Q

What temperature must be exceeded to cause dipoles to un-freeze?

A

the curie temperature.

71
Q

What does rapidly changing polarity (alternative current) cause to the dipoles?

A

Constant expansion and contraction causing the CONVERSE PEIZO ELECTRIC EFFECT.

72
Q

Will a thicker transducer crystal produce higher or lower frequencies?

A

Low

73
Q

Are transducers typically multi or single frequency?

A

single

74
Q

If the crystal was placed directly onto the skin, about __% of the ultrasound would be reflected.

A

80%

75
Q

Other than gel what else does the transducer use to lower differences in acoustic impedence?

A

the matching layer.

76
Q

why is the matching layer sometimes called the ‘1/4 wave matching layer?

A

IT HAS A THICKNESS OF ONE QUARTER OF ITS WAVELENGTH

77
Q

What layer is used in pulsed US mode?

A

Dampening layer

78
Q

WHat is the purpose of the dampening layer?

A

To stop the transducer making sounds after it is turned off… to keep the pulses at 2-5 cycles.

79
Q

What does the backing layer improve in US?

A

AXIAL RES.

80
Q

Will a continuous transducer produce multiple frequencies?

A

No, they are single frequencies.

81
Q

What frequencies does pulsed transducers produce?

A

a range of frequencies.

82
Q

which pulse has a greater bandwidth?

A

shorter pulses

83
Q

Will a longer SPL have less or more cycles?

A

More.

84
Q

Will a longer SPL have a shorter or longer bandwidth?

A

Shorter/ narrow.

85
Q

typically a longer bandwidth will increase/ decrease axial resolution?

A

Increase as it has a shorter SPL

86
Q

Which array is used more?

A

phased

87
Q

Frequency of linear array

A

5-13 MHz

88
Q

Frequency of curvilinear array

A

1-8 MHz

89
Q

What is the advantage of only activating certain crystals?

A

can create a narrow beam = increased lateral resolution

90
Q

Frequency of phased array and what they are used for typically?

A

2-8 MHz.

good for cardiac images, small area i.e. between ribs.

91
Q

Frequency of endocavitary array

A

8-13 MhHz

92
Q

Why is CMUT considered better than PZT?

A

better acoustic matching.

 Wider bandwidth capabilities (smaller pulse lengths)
 Potentially improved axial resolution
 Potentially lower costs with easier fabrication,

93
Q

Why is a focused beam desirable in US?

A

 Produces pulses with a small diameter.
 Gives better visibility of detail in the image.
 Best detail will be obtained for structures within the focal zone.
 Distance between the transducer and the focal zone is the focal depth.

94
Q

Two zones in the unfocused beam?

A

Near : Frensel zone

Far : Fraunhofer Zone

95
Q

What is the near field the same as?

A

same diameter of the transducer.

96
Q

What is the NZL and what affects the length of it?

A

NEAR ZONE LENGTH

Related to diameter of the transducer.

wavelength

97
Q

what will an increase in frequency do to the NZL?

A

increase it

98
Q

What two things decrease the divergence at the far field?

A

Increasing diameter

and increasing frequency,

99
Q

What affects the diameter of the US pulse?

A

amount of crystals activated or number we use

100
Q

What affects the width of the US beam

A

This is the length and related to the number of cycles we have

101
Q

For a single element transducer, side lobes are about __% of the main beam energy

A

15%

Instrumentation 2 (4 decks)

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