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LMC Ultrasound > Physics Final > Flashcards

Physics Final Flashcards

1
Q

T/F Macro means bigger and micro means smaller

A

True

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2
Q

T/F The symbol for millions is mega and millionths is micro

A

True

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3
Q

T/F The symbol for hundreds is giga and the symbol for hundredths is hecto

A

False; hundreds is hecto (h), hundredths is centi (c)

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4
Q

T/F A wave with a frequency of 15,000 MHz is ultrasonic

A

True

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5
Q

T/F If the power of a wave is halved, the intensity is reduced to one-fourth its original value

A

False; intensity is the power of a beam divided by its cross-sectional area. If we halve the power, we will halve the intensity

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6
Q

T/F If the amplitude of a wave is increased to 3 times its original value, the intensity is increased by 6 times

A

False; Intensity is proportional to the amplitude squared. If we triple the amplitude, we increase the intensity by a factor of nine.

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7
Q

T/F Propagation speed is determined by the medium

A

True

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8
Q

T/F Propagation speed increases as frequency increases

A

False; they are unrelated

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9
Q

T/F We need one intensity to calculate decibels

A

False; we need two intensities to calculate decibels

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10
Q

T/F As the path length increases, attenuation of US in soft tissue increases

A

True

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11
Q

T/F Spatial peak intensity is always lower than the spatial average intensity

A

False; Spatial peak intensity is always higher than the spatial average intensity

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12
Q

T/F In addition to location within the beam, sound wave intensities also vary over time

A

True

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13
Q

T/F SPTA intensity is the most relevant intensity with respect to tissue heating

A

True

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14
Q

T/F The duty factor is a unit less number with a value between 0 and 1

A

True

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15
Q

T/F There are two different methods to measure and report intensities

A

False; there are 6 different methods to measure and report intensities

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16
Q

T/F The duty factor for a pulsed ultrasound system is 2%.

A

False; with anatomic imaging the duty factor is 0.2%

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17
Q

T/F An ultrasound beam has the same intensity at different depths or at different side to side locations within the beam

A

False; the beam will have different intensities

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18
Q

T/F At a particular depth, the center of a sound beam is more intense than the edges

A

True

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19
Q

T/F Temporal peak intensity is maximum in time

A

True

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20
Q

How many hertz is 3MHz?

A

3,000,000 Hz

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21
Q

How much bigger is a billion than a million?

A

1,000

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22
Q

What are the units of wavelength?

A

unit of length, mm or m

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23
Q

What are the units of frequency?

A

Hertz; Hz

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24
Q

What are the units of intensity?

A

W/cm^2

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25
Q

What are the units of propagation speed?

A

units: m/s, mm/ μs, or any distance divided by time

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26
Q

What are the units of period?

A

units of time, microseconds, seconds, hours, or days

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27
Q

Of the following which grouping is determined by the sound source?

A

Amplitude, power, intensity

Period, frequency

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28
Q

If the intensity remains the same while the power is doubled, what happens to the beam area?

A

Doubles

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29
Q

A sound beam travels a total of 10cm in 2 seconds. What is the speed of the sound in this medium?

A

5cm/sec

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30
Q

What term describes the time from the start of a pulse to the end of that pulse?

A

Pulse duration

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31
Q

Pulse Repetition frequency is the reciprocal of..

A

Pulse Repetition Period

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32
Q

db is a mathematical representation with a __scale?

A

Logarithms

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33
Q

Rayleigh scattering is related to?

A

Frequency raised to the fourth power

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34
Q

Which of these media have the greatest attenuation and the slowest speed?

A

Bone

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35
Q

Which of the following mathematically describes the physics of refraction?

A

Snell’s Law

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36
Q

Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with ______?

A

Lower frequency

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37
Q

Characteristics of an imaging transducer

A
  • Pulses with short duration and length
  • Uses backing material to limit ringing
  • Reduced sensitivity
  • Wide bandwidth or broadband
  • Lower Q-factor
  • Improved axial resolution
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38
Q

When PZT’s temperature exceeds the Curie point, the PZT is _______?

A

Depolarized

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39
Q

PZT in an ultrasound transducer is also known as

A

Ceramic, active element, or crystal

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40
Q

Which of the following describes the transducer component that reduces the “ringing” of the pulse?

A

Damping element or backing material

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41
Q

Mathematically, the Q factor is the main frequency divided by _____?

A

Bandwidth

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42
Q

Imaging transducers can also be referred to as ______?

A

Pulsed wave transducers

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43
Q

Which of the following crystals will produce sound with the lowest frequency?

A
  • Thicker PZT crystal

- PZT with lower speeds

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44
Q

The damping material in the transducer improves the system’s _____ resolution?

A

Axial

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45
Q

If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is ____MHz.

A

With pulsed wave transducers, the frequency of sound is not determined by the electrical signal.

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46
Q

The impedance of a transducer active element is 1,900,000 Rayls, and the impedance of the skin is 1,400,000 Rayls. What is an acceptable impedance of the matching layer?

A

1,726,000 Rayls

*The impedance of the matching layer is between that of the active element and the skin

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47
Q

Of the following, which transducer component is a thin barrier of cork or rubber that isolates or “uncouples” the internal components of the transducer from the case?

A

Acoustic insulator

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48
Q

In an imaging transducer, what is the purpose of attaching the backing material to the PZT?

A

Reduces the ringing of the PZT

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49
Q

Which of the following probes creates a beam with the deepest focus?

A
  • Higher frequency

- Larger diameter

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50
Q

Which of the following probes creates a beam with more divergence?

A
  • Lower frequency

- Smaller diameter

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51
Q

Which of the following determines the frequency of sound created by a pulsed wave transducer?

A
  • Speed of sound in the PZT

- Thickness of the PZT

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52
Q

Which of the following determine the spread of a sound beam in the far field?

A
  • Transducer diameter

- Frequency of the sound

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53
Q

Of the following which term does not belong with the others?
Focus, end of the near zone, end of the Fraunhofer zone, middler of the focal zone

A

The end of the Fraunhofer zone is the very end of the sound beam

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54
Q

The frequency of a transducer does not change. If the diameter of the new piezoelectric increases, what happens to the wavelength?

A

No change

55
Q

Imaging to a greater depth of view requires _____ listening?

A

Longer

56
Q

When reporting a beam’s intensity at the location where it is maximum is referred to as?

A

Spatial peak intensity

57
Q

The highest temporal intensity is which of the following?

A

Temporal peak

58
Q

Choose the units for reporting intensity from the following

A

W/cm^2

59
Q

Rank of intensities from largest to smallest

A

SPTP-Im-SPPA-SPTA-SATA

60
Q

Which of the following is measured where intensity is maximum and averaged over all time?

A

SPTA

61
Q

Which intensity is measured over the entire cross-sectional area of the sound beam, and over all time?

A

SATA

62
Q

Synonyms for normal incidence

A
  • Perpendicular
  • Orthogonal
  • Right angle
  • 90 degrees
63
Q

The intensity of the sound wave at the instant prior to striking a boundary is referred to as?

A

Incident intensity

64
Q

The portion of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling is referred to as the?

A

Transmitted intensity

65
Q

The percentage of the US intensity that is allowed to pass through when the beam reaches a boundary between two media is referred to as?

A

Intensity transmission coefficient (ITC),

66
Q

A sound wave with an intensity of 50W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient?

A

100%

67
Q

The intensity reflection coefficient of sound is 99.9%. What percent of sound is transmitted into the body?

A

0.1%

68
Q

Specular reflections arise when the interface is ______?

A

Smooth

69
Q

What do we know about oblique incidence?

A

Nothing!

70
Q

Transmission with a bend is referred to as?

A

Refraction

71
Q

Snell’s law describes what physics?

A

Refraction

72
Q

Sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?

A

Refraction will not occur when the speeds of the two media are identical

73
Q

What processes occur as the ultrasound passes through all media?

A
  • Reflection
  • Scattering
  • Absorption
74
Q

Two waves are traveling through a medium and arrive at a location at the same time. What event takes place?

A

Interference

75
Q

The percentage of time that a system is transmitting a pulse refers to which of the following?

A

Duty factor

76
Q

A 3MHz sound beam travels through two media. It attenuates 5 dB in medium A and 6 dB in medium B. What is the total attenuation that the sound beam undergoes as it travels through both media?

A

11 dB

* 5dB+6dB=11dB

77
Q

Which of these are considered the dominant contributor to attenuation?

A

Absorption

78
Q

Hertz is a unit of measurement used to describe what wave characteristic?

A

Frequency

79
Q

A low frequency transducer is best at imaging which anatomical structure?

A

OB/AB

80
Q

Which of the following is the best estimate for attenuation coefficient of sound traveling in soft tissue?

A

Is the one-half the frequency

Atten. coef. = 0.5 dB/cm/MHz

81
Q

Attenuation is determined by two factors

A
  • Path length

- Frequency of sound

82
Q

With longer distances and higher frequencies you have?

A

More attenuation

83
Q

With shorter distances and lower frequencies you have?

A

Less attenuation

84
Q

Because attenuation means a weakening or a decrease, the dbs must be?

A

Negative

85
Q

Which term best describes redirection of sound in many directions?

A

Scattering

86
Q

Reflections from a smooth reflector are referred to as?

A

Specular Reflection

87
Q

When a boundary is rough, reflected sound is disorganized and random, also called?

A

Diffuse reflection, or backscatter

88
Q

Rayleigh scattering increases dramatically with increasing frequency, which is the relation?

A

Its proportional

89
Q

Acoustic Impedance is equal to?

A

Density (kg/m^3) * prop. speed (m/s)

90
Q

A sound wave is created by the transducer, reflects off of an object and returns to the transducer. The depth of the reflector is 10 cm. The round trip time is 2 seconds. What is the speed of sound in the medium?

A

10 cm/sec
*10cm + 10 cm= 20cm
20cm/2 sec=10 cm/sec

91
Q

The time needed for a pulse to travel to and from the transducer and the reflector is called?

A

Time-of-flight

92
Q

A sound wave is created by the transducer, reflects off an object and returns to the transducer in 52 microseconds. How deep is the object and what is the total distance traveled?

A

4cm, 8 cm

93
Q

The maximum imaging depth during an ultrasound exam is 5 cm. The sonographer adjusts the depth to 10cm. What happens to pulse repetition frequency?

A

It will 1/2. PRF is inversely related to the maximum imaging depth

94
Q

The maximum imaging depth during an ultrasound exam is 4cm. The sonographer adjusts the imaging depth to 8 cm. What happens to the pulse repetition period?

A

It will double. PRP is directly related to the maximum imaging depth

95
Q

A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The time of flight is 130 microseconds. What is the maximum PRF?

A

7,700 Hz

*PRF(Hz) = 77,000 cm/s / 10cm

96
Q

A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The go return time is 39 microseconds. What is the total distance traveled?

A

6 cm

97
Q

Axial resolution deals with structures that are ______ to the sound beam.

A

Front-to-back, or parallel

98
Q

As frequency increases, the numerical value of LARRD resolution _______?

A

Decrease

99
Q

Which of the following has the highest axial resolution?

A
  • Less ringing

- Higher frequency

100
Q

Superior axial resolution is associated with the following?

A
  • Shorter spatial pulse length
  • Shorter pulse duration
  • Higher frequencies (short wavelengths)
  • Fewer cycles per pulse (less ringing)
  • Lower numerical values
101
Q

Two different transducers create pulses. Both transducers create sound with a frequency of 5MHZ. Which of the following is more likely to create a better image in regards to axial resolution?

A

The one with fewer cycles per pulse and shorter pulses

102
Q

Which of the following transducers will create the lowest numerical value of axial resolution?

A

Highest frequency

103
Q

Effects of focusing

A
  • Beam diameter in near field and focal zone is reduced
  • Focal depth is shallower
  • Beam diameter in the far zone increases
  • Focal Zone is smaller
104
Q

Display modes

A

A-mode –Amplitude
B-mode –Brightness
M-mode –Motion

105
Q

What is the only display mode that provides information regarding reflector motion with respect to time?

A

M-mode

106
Q

What display mode looks like a big city skyline?

A

A-mode

107
Q

What display mode was the first form of gray scale imaging?

A

B-mode

108
Q

A-mode display axes

A

X-axis: depth of the reflector

Y-axis: amplitude of the reflected signal

109
Q

With M-mode, what is displayed on the x-axis?

A

Time

110
Q

With B-mode, what is displayed on the y-axis?

A

Nothing! -trick question

111
Q

Depth is displayed on what axis of M-mode?

A

Y-axis

112
Q

Which display mode uses the z-axis?

A

B-mode; Amplitude

113
Q

With B-mode, what is displayed on the x-axis?

A

Depth of the reflector

114
Q

Acoustic propagation properties

A

The effects of the medium upon the sound wave

115
Q

Biologic effects

A

The effects of the sound wave upon the biologic tissue through which it passes

116
Q

Sound must travel through a medium, where molecules are alternately _____ and _____

A

Compressed and rarefied

117
Q

Acoustic variables of a sound wave

A
  • Pressure
  • Density
  • Distance
118
Q

Acoustic parameters of a sound wave

A
  • Period
  • Frequency
  • Amplitude
  • Power
  • Intensity
  • Wavelength
  • Propagation speed
119
Q

Stiffness

A

The ability of an object to resist compression

120
Q

Density

A

The relative weight of a material

121
Q

Materials that are stiff but not dense will have the..

A

Fastest speed

122
Q

Materials that are not stiff and very dense will have the..

A

Slowest speed

123
Q

Five parameters that describe pulsed sound

A
  • Pulse duration
  • Pulse repetition period
  • Pulse repetition frequency
  • Duty factor
  • Spatial pulse length
124
Q

Shallow imaging

A
  • Less listening
  • Shorter PRP
  • Higher PRF
  • Higher duty factor
125
Q

Deep imaging

A
  • More listening
  • Longer PRP
  • Lower PRF
  • Lower duty factor
126
Q

Five words that are related to the intensities of pulsed waves

A
  • Spatial
  • Peak
  • Average
  • Temporal
  • Pulsed
127
Q

3 dB means..

A

Double

128
Q

10 dB means..

A

ten times larger

129
Q

-3 dB means..

A

half

130
Q

-10 dB means..

A

one-tenth

131
Q

T/F A tissue’s impedance is calculated, not measured

A

True

132
Q

What two physical principles always apply to reflection with oblique incidence?

A
  • Conservation of energy

- Reflection angle=incident angle

133
Q

Refraction occurs only if conditions are satisfied:

A
  • Oblique incidence

- Different propagation speeds of the two media

134
Q

Which of these media have the greatest attenuation and the fastest speed?

A

Bone

LMC Ultrasound (32 decks)

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