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DMS 101- Ultrasound Physics > Test 2- both powerpoints & all drills > Flashcards

Test 2- both powerpoints & all drills Flashcards

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1
Q

A …….. is any device used to convert energy from one form to another.

For transduction to occur, a change from one form of energy must also take place, such as a conversion from mechanical to electrical energy or vice versa.

A

transducer

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2
Q

Each active element requires how many electrical contacts

A

two

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3
Q

………….. is the electric charge that accumulates in certain solid materials (such as crystals & certain ceramics) in response to applied mechanical stress (vibrations)

A

Piezoelectricity

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4
Q

possible natural ultrasound crystal material

A

Quartz
Rochelle salts
Tourmaline

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5
Q

Ultrasound Crystals
MAN-MADE MATERIALS

A

Barium titanate
Lead metaniobate
Lead titanate
Lead zirconate titanate (PZT)

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6
Q

crystal material that is most commonly used because of its high conversion efficiency.

A

PZT. Lead zirconate titanate

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7
Q

If PZT is heated about the curie temperature, approximately ……………., it will lose the piezoelectric component of the crystal (and thus depolarize).

A

360C or 680 degrees F

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8
Q

Operating frequency is sometimes called ………..

A

resonance frequency

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9
Q

The main factor in the operating frequency comes from the …………… and not so much the propagation speed of the crystal.

A

thickness of the element

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10
Q

frequency formula

A

Propagation speed (mm/μs) /
Wavelength (mm)

or Propagation speed (mm/μs) /
2 X thickness (mm)

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11
Q

Propagation speed is typically …………..

hint measurements

A

Propagation speed is typically 4 to 6 mm/μs

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12
Q

As the propagation speed of the crystal increases the operating frequency of the transducer …………..

A

increases

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13
Q

The shorter the pulse (fewer cycles) the (MORE OR LESS) frequencies are present in the pulse—wider bandwidth

A

more

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14
Q

………….. also known as the first harmonic

A

fundamental frequency

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15
Q

When THI is activated, only the ……….. frequency component is detected, greatly improving the beam profile.

–Backscattered echoes (noise) are very low intensity and do not generate any significant harmonics: this improves the signal to noise ratio (SNR) thus improving contrast resolution
–Side lobes disappear and the beam becomes narrower resulting in improved lateral resolution.
–Because the beam becomes narrower in the orthogonal plane as well as the scan plane, slice thickness is reduced

A

harmonic

info about harmonics to commit to memory

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16
Q

Damped pulse increases …………

A

bandwidth

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17
Q

Facts about Damping:

Shortens the pulse duration
Shortens the spatial pulse length
Improves picture quality/resolution
Increases bandwidth
Decreases Q factor
Decreases the transducer’s sensitivity to reflected echoes

A

study

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18
Q

Decreases (improves) axial resolution by decreasing PD & SPL (wavelength)

A

damping element

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19
Q

Backing material must have …………………………. impedance of the crystal for maximum sound transmission

A

similar or identical acoustic

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20
Q

An electronic means to suppress ringing
A voltage pulse of opposite polarity is applied to the crystal
Counteracts the expansion and contraction of the crystal stimulated by the first pulse

A

dynamic damping

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21
Q

a unitless number that represents the ability of a transducer to emit a “clean” ultrasound frequency

A

quality factor
q factor

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22
Q

Q Factor =

A

Operating Frequency (MHz) / Bandwidth

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23
Q

Specifically, the optimum thickness of the matching layer is …………… of a wavelength

A

1/4th

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24
Q

Provides physical protection for the transducer components

Reduces EM interference (noise), which prohibits the detection of weak echoes

A

transducer housing

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25
Q

Memorize this chart!!

Imaging Transducer Characteristics

A

-Damping is effective (backing material)
-Short pulse length & duration
-Low sensitivity
-Wide bandwidth
-Low Q factor
-Decreased output power

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26
Q

You ALWAYS want the (LOWEST OR HIGHEST) resolution probe possible.

A

highest

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27
Q

BURST EXCITED OR SHOCK EXCITED

–Cycle or two of alternating voltage
–PRF of sound produced = PRF of driving voltage
–Produces wider bandwidth
–Can be used to selectively operate the same transducer at more than one frequency (multihertzing)

A

BURST EXCITED

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28
Q

BURST EXCITED OR SHOCK EXCITED

Usually 2-3 cycles
Narrow bandwidth
Operates at single frequency

A

SHOCK EXCITED

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29
Q

The resonance frequency of the transducer depends on….

A

The thickness of the piezoelectric element

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30
Q

Which statement is INCORRECT for piezoeletric transducers?

A- Convert sound waves to eletrical signals
B- Responds equally to most frequencies
C- Converts electrical signals to sound waves
D- Vibrates when an electrical signal is applied

A

B- Responds equally to most frequencies

Fact: Most piezoelectric transducers have a resonance frequency that depends on the thickness of the element. The crystal responds best at the resonant frequency

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31
Q

Which of the following will not change if you change the transducer to one having a different frequency?

A- Amount of attenuation
B- Amount of scatter
C- Speed of sound
D- Axial resolution
E- Lateral resolution

A

C- Speed of sound

Scatter, attenuation and resolution all depend on frequency.
Don’t let a lot of choices take your mind of a principal that is considered a constant in ultrasound–take one when you can get it!! :o)

The MEDIUM always determines the speed of sound.

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32
Q

Before we can use a ceramic transducer element, such as lead zirconate titanate, it must be:

A

polarized

Polarized by heating above the Curie temperature, applying a strong electric field and then cooling to hold the polarization.

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33
Q

The advantage of composite transducer material over solid PZT is that they:

A- are easier to manufacture
B- produce lower intensity ultrasound beams
C- have a lower impedance and a wider bandwith
D- have better resolution and smaller slice thickness

A

C- have a lower impedance and a wider bandwith

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34
Q

To produce a sound beam, a pulsed transducer is made to oscillate by:

A

Applying an electrical pulse

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35
Q

The backing layer:

A

dampens the transducer

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36
Q

The purpose of the quarter-wave matching layers on the transducer surface is to:

A

Improve transmission into the medium

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37
Q

The manufacturer is selecting a material to use as a matching layer on a transducer. The piezoelectric element has an impendance of 30 x 106 rayls. The impedance of soft tissue is 1.6 x 106 rayls. The best material for the matching layer likely has an impedance of about:

1.0 x 106 rayls
6.9 x 106 rayls
32 x 106 rayls
121 x 106 rayls

A

6.9 x 106 rayls

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38
Q

Axial resolution is most closely associated with:

Transducer size
Transducer focusing
Beam width
Pulse duration

A

Pulse duration

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39
Q

For a fixed frequency, increasing the pulse duration does what to the frequency bandwidth?

A

Decreases it

Decreases the bandwidth. Think about music, the longer you hear the note the more there is one tone that can be heard. Short pulse creates a broad range

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40
Q

Ultrasound transducers typically generate pulses of how many cycles?

A

2-3

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41
Q

The beam of an unfocused transducer diverges:

A

In the Fraunhofer zone

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42
Q

Greater beam divergance in the far field results in:

A- Better axial resolution
B- Poorer axial resolution
C- Better lateral resolution
D- Poorer lateral resolution

A

D- Poorer lateral resolution

Narrow beam width=better lateral resolution, Wider beam width=poorer lateral resolution

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43
Q

Apodization helps reduce:

A

side lobes

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44
Q

If the frequency doubles but the crystal diameter remains the same for a single element non-focused transducer, the near field:

A

Doubles

If the frequency double, the wavelength halves.

The NZL is inversely proportional to wavelength, so it will double when the wavelength halves.

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45
Q

Widening of the sound beam is demonstrated in the __________________.

A

Fraunhofer zone

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46
Q

Weak beams emitted from a linear sequenced array transducer are termed:

A

grating lobes

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47
Q

The fundamental frequency of the pulsed wave is determined by

A

thickness and propagation speed of the element

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48
Q

Heat sterilization is not recommended for diagnostic transducers because:

A

The piezoelectric properties will be lost

49
Q

An electronic means to suppress the elements from ringing describes:

A

dynamic damping

50
Q

More frequencies and wavelengths are present in:

A

shorter pulses

51
Q

The width of the transducer is 5.0cm. The width of the focal point is ______.

A

2.5 cm

52
Q

Reducing the impedance difference between the crystal and the skin is the primary function of which of the following transducer components?

A

matching layer

53
Q

A sound beam demonstrates the most uniform intensity in the:

A

far zone

-The far zone has the most uniform intensities
-Intensities have much variability in the near zone
-The focus has the greatest intensity

54
Q

Which of the following changes will improve temporal resolution

A

decrease in imaging depth

55
Q

The distance from the face of the transducer to the point of spatial peak intensity is called the:

A

near zone length

56
Q

Which of the following best describes channels?

A

multiple transducer elements with individual wiring and system electronics

57
Q

Which of the following determines the diameter of the focus?

A

diameter of the transducer

58
Q

The impedance of the damping layer is____________

A

similar to the element’s

59
Q

The purpose of the backing material in the transducer assembly is to:

A

reduce the number of cycles in a pulse

60
Q

Focusing of the sound beam is directly related to_________

A

lateral resolution

61
Q

Contains an oscillating component that is immersed in a coupling liquid within the transducer assembly.

A

Mechanical Transducer

62
Q

T or F
Within transducers, there is a conversion zone which concentrates the sound beam into a smaller beam area than would exist otherwise.

A

True

Within transducers, there is a FOCUS which concentrates the sound beam into a smaller beam area than would exist otherwise.

63
Q

Waves of very high frequency (2MHz or greater)

A

Ultrasound

64
Q

___________________are the reflections of the sound beam as it travels through the media.

A

Echoes

65
Q

T or F
Propagation in gases is poor because the molecules are too widely spaced which is why lung does not image well with ultrasound.

A

true

66
Q

______________________is the time it takes for 1 cycle to occur; the inverse of frequency.

A

period

67
Q

The deeper your sound goes into the body, the greater the _________ the sound beam will incur.

A

attenuation

68
Q

A device which houses the element for transmitting and receiving ultrasound waves.

A

Transducer

69
Q

The number of complete cycles per second (Hertz)

A

Frequency

70
Q

Sound waves do not exist in a _________________,

A

Vacuum

71
Q

Good__________________________ is achieved with short spatial pulse lengths.

A

Axial Resolution

72
Q

The ultrasound beam undergoes a progressive weakening as it penetrates the body due to absorption, scattering and beam spread.

A

Attenuation

73
Q

Allows the sweeping of the ultrasound beam through the tissues rapidly and repeatedly by oscillating a transducer crystal(s).

A

Mechanical Transducer

74
Q

An acoustic wave that has a frequency higher than the upper limit of human hearing.

A

Ultrasound

75
Q

____________________ is propagated via waves of compression and rarefaction, and requires a medium (tissue) for travel.

A

Utrasound

76
Q

_______________________ is a longitudinal, mechanical wave that carries variations of quantities referred to as acoustic variables.

A

ultrasound

77
Q

Refers to the amount of amplification of the returning echoes.

A

gain

78
Q

________________operate on piezoelectricity; meaning that some materials (ceramics, quartz) produce a voltage when deformed by an applied pressure, and reversely results in a production of pressure when these materials are deformed by an applied voltage.

A

transducer

79
Q

Power is the rate of energy transferred. The power is proportional to the wave amplitude _____________.

A

squared

Power is the rate of energy transferred. The power is proportional to the wave amplitude squared. Unit: watts (W).

power ∼ amplitude2

80
Q

Not associated with bioeffects, this is a better option than increasing power when needing to amplify the brightness of the returning echoes and subsequent ultrasound image on our screen. Amplify the brightness by adjusting the __________________

A

gain

81
Q

If more penetration is required you need to use a lower ________________ with the sacrifice of some resolution.

A

frequency

82
Q

Good ___________________ is achieved with narrow acoustic beams.

A

Lateral Resolution

83
Q

__________________________ is the minimum required reflector separation along the direction of propagation required to produce separate reflections.

A

axial resolution

84
Q

The shape of the beam is varied and is different for each transducer frequency. There is a fixed focused region of the ultrasound beam called the focal zone of that transducer and that is where the best ____________ resolution can be achieved with that particular transducer.

A

lateral resolution

85
Q

Convert one form of energy to another.

A

transducer

86
Q

A gel couplant is used between the skin of the subject and the transducer face otherwise the sound would not be transmitted across the air-filled gap.

A

true

87
Q

The higher the _________________, the less depth penetration; however, the resolution is improved.

A

frequency

88
Q

Prone to leakage and breakage, this probe is not commonly used in diagnostic scanning.

A

Mechanical Transducer

89
Q

__________________________ is the minimum reflector separation perpendicular to the direction of propagation required to produce separate reflections.

A

Lateral Resolution

90
Q

Weakening of sound energy dependent on frequency, tissue density, and the number and types of interfaces

A

Attenuation

91
Q

____________________ describes how many times the acoustic variable (whether it be pressure, density, particle motion, or temperature) changes in one second.

A

Frequency

92
Q

T or F
Ultrasound can be continuous or pulsed. In the continuous mode, the vibratory motions are produced by the source in an uninterrupted stream, whereas in the pulsed mode, the sound is delivered in a series of packets, or pulses.

A

True

93
Q

Does intensity vary throughout beam?

A

yes

94
Q

Beam diameter depends on:

Hint: 3 things

A

Wavelength
Transducer diameter
Distance from the transducer

95
Q

Space between the transducer and the focus is called:

A

Near zone
Near field
Freznal zone

96
Q

Region beyond the near zone is called:

A

Far zone
Far field
Fraunhofer zone

97
Q

Focusing can only be accomplished in the ………… zone of a transducer

A

near

98
Q

Near zone length =

A

(crystal diameter)^2 X Frequency / 6

99
Q

What is the length of the near zone if the diameter of the
crystal is 6mm and the frequency of the transducer is
2 MHz?

A

6mm^2 x 2MHz / 6

36mm x 2MHz / 6

72/6 = 12mm or 1.2cm

100
Q

an increase in ______ or _______ would increase focal length

A

crystal diameter or frequency

101
Q

A (small/large) diameter crystal will produce a more divergent beam in the far field

A

small

102
Q

Recognizes that waves are circular at the front and if two or more points of light or sound are fired at the same time each wavelet will overlap waves running right next to it
When these beams overlap they end up producing one large beam of sound, just like LED lights do in headlights:

A

Huygens’ Principle

103
Q

The ability to separate objects in space, time, or by strength

A

resolution

104
Q

separation of objects in space (distance)

A

detail resolution

which include lateral and axial resolution

105
Q

Axial Resolutions also called:

A

LARD acronym
Longitudinal
Axial
Range
Depth

106
Q

Axial resolution (SPL) improves with (lower/higher) frequency

A

higher

107
Q

Axial resolution =

A

spatial pulse length (mm) / 2

108
Q

how does frequency affect axial resolution and why

A

increase freq improved axial resolution (decreases it)

AR= SPL / 2
but SPL =cycles x wavelength
AND Wavelength= propagation speed / freq

109
Q

Axial resolution improves with (shorter/longer) spatial pulse length

A

shorter

110
Q

Axial resolution improves with (shorter/longer) wavelength

A

shorter

111
Q

Narrow pulses provide the ability to accurately identify structures that lie close together, side-by-side.

lateral or axial

A

lateral resolution

112
Q

………… resolution is approximately equal to beam diameter

A

lateral

113
Q

lateral resolution AKA

3 other names

A

acronym LATA
Lateral
Angular
Transverse
Azimuthal

114
Q

which is better…..axial or lateral resolution

A

axial resolution
being able to distinguish from objects behind each other

115
Q

how to improve lateral resolution?

A

focusing

116
Q

Occur with SINGLE element transducers

Do not affect most pulsed ultrasound systems (CW)

Created by acoustic energy not in/on the main beam axis

If strong, will degrade lateral resolution

A

Side Lobes

117
Q

Occur with transducer arrays

Created by acoustic energy not in/on the main beam axis

Will add misplaced reflectors on screen (machine thinks that the reflector was in the path of the main beam and therefore puts it there on the screen

Transducers use ‘sub-dicing’ to correct

A

Grating Lobes

118
Q
A

DMS 101- Ultrasound Physics (4 decks)

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