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Ultrasound Flashcards

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1
Q

Mechanical energy that propagates thru a continuous, elastic medium by the compression and rarefaction of particles that comprise it

A

Sound

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2
Q

Generated by a mechanical displacement in compressible medium, which is modeled as an elastic spring

A

Ultrasound energy

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3
Q

Shown as a function of time, resulting in areas of compression and rarefaction with corresponding variations in positive and negative pressure amplitude

A

Energy propagation

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4
Q

Distance between compressions or rarefactions or between any two points that repeat on the sinusoidal wave of pressure amplitude

A

Wavelength

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5
Q

Number of times the wave oscillates thru one cycle each second

A

Frequency

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6
Q

Sound waves with frequencies less than 15 cycles per second are called

A

Infrasound

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7
Q

Frequency range of 15 and 20 kHz comprises the

A

Audible acoustic spectrum

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8
Q

Frequency range above 20 kHz are

A

Ultrasound

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9
Q

Medical ultrasound is at what frequency range

A

2-10 MHz

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10
Q

Specialized medical ultrasound applications are up to what frequency range

A

50 MHz

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11
Q

Time duration of one wave cycle an is equal to 1/f

A

Period

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12
Q

Distance travelled by wave per unit time and is equal to the wavelength divided by the period

A

Speed of sound

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13
Q

A highly compressible medium such as air, has a high or low speed of sound?

A

Low speed of sound

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14
Q

A less compressible medium such as bone, has a higher or lower speed of sound?

A

Higher speed of sound

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15
Q

True or false: ultrasound frequency is unaffected by changes in sound speed as the acoustic beam propagates thru different media

A

True

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16
Q

True or false: ultrasound wavelength affects the spatial resolution achievable along the direction of the beam

A

True

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17
Q

Provides better resolution and image detail than a low frequency beam

A

High frequency ultrasound beam

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18
Q

Interaction of 2 or more separate ultrasound beams in a medium can result in

A

Constructive and/or destructive wave interference

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19
Q

Position of the periodic wave with respect to a reference point

A

Phase

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20
Q

Amount of constructive or destructive interference depends on several factors, but the most are the

A

Phase and amplitude of interacting beams

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21
Q

Defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of soundwave

A

Pressure amplitude

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22
Q

In diagnostic ultrasound applications, the compressional amplitude significantly _______ the rarefactional amplitude

A

Exceeds

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23
Q

SI unit for pressure is the

A

Pascal (Pa) defined as 1 newton per square meter

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24
Q

Relative intensity and pressure levels are described as a logarithmic ratio, the

A

Decibel

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25
Q

Occurs at tissue boundaries where there is a difference in the acoustic impedance of adjacent materials

A

Reflection

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26
Q

Describes the direction of the transmitted ultrasound energy with nonperpendicular incidence

A

Reflection

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27
Q

Occurs by reflection or refraction, usually by small particles within the tissue medium, causes the beam to diffuse in many directions and gives rise to the characteristic texture and gray scale in the acoustic image

A

Scattering

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28
Q

Refers to loss of intensity of the ultrasound beam from absorption and scattering in the medium

A

Attenuation

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29
Q

Process whereby acoustic energy is converted to heat energy, whereby sound energy is lost and cannot be recovered

A

Absorption

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30
Q

SI unit for acoustic impedance is

A

Kg/m2s

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31
Q

Gives rise to differences in transmission and reflection of ultrasound energy, which is the means for producing an image using pulse echo techniques

A

Acoustic impedance

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32
Q

Describes the fractiom of sound intensity incident on an interface that is reflected

A

Reflection coefficient

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33
Q

Change in the direction of transmitted ultrasound energy at a tissue boundary when the beam is not perpendicular to the boundary

A

Refraction

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34
Q

Arises from objects and interfaces within a tissue that are about the size of the wavelength or smaller, and represent a rough or nonspecular reflector surface

A

Scattering

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35
Q

A smooth boundary between two media, where the dimension of the boundary between two media, where the dimensions of the boundary are much larger than the wavelength of the incident ultrasound energy

A

Specular reflector

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36
Q

These areas usually have a greater number of scatterers, larger acoustic impedance differences and larger scatterers

A

Hyperechoic areas

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37
Q

Specular reflection is dependent or independent? of frequency

A

Independent

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38
Q

Attenuation coefficient is expressed in units of

A

dB/cm

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39
Q

Ultrasound is produced and detected with a ______, comprised of one or more ceramic elements with electromechanical properties and peripheral components

A

Transducer

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40
Q

Part of the transducer that converts electrical energy into mechanical energy to produce ultrasound and mechanical energy into electrical energy for ultrasound detection

A

Ceramic element

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41
Q

Functional component of the transducer, which is often a crystal or ceramic

A

Piezoelectric material

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42
Q

Measures the magnitude of voltage, which is proportional to the incident mechanical pressure amplitude

A

Surface electrodes

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43
Q

Common piezoelectric ceramic in medical imaging

A

Lead-zirconate-titanium

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44
Q

Higher frequencies are achieved with thinner/thicker elements

A

Thinner elements

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45
Q

Thicker elements produce what type of frequency

A

Lower frequencies

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46
Q

Layered at the back of the piezoelectric element, absorbs the backward directed ultrasound energy and attenuates stray ultrasound signals from the housing

A

Damping block

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47
Q

Creates short spatial pulse length, which is necessary to preserve detail along the beam axis (axis resolution)

A

Damping block

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48
Q

High Q transducer has a _____bandwidth and corresponding ______ spatial pulse length

A

Narrow bandwidth

Long SPL

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49
Q

A low Q Transducer has a _____ bandwidth and ______ spatial pulse length

A

Wide bandwidth and short spatial pulse length

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50
Q

Continuous-wave ultrasound transducers have a very ______ q characteristics

A

High

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51
Q

Provides the interface between the raw transducer element and the tissue and minimizes the acoustic impedance differences between the transducer and the patient

A

Matching layer

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52
Q

Broadband multi frequency transducers have bandwidth that exceeds ____% of the center frequency

A

80%

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53
Q

Located adjacent to the backside of the transducer and limits the vibration of the element to a small number of cycles

A

Damping block

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54
Q

Described as percentage of the center frequency

A

Bandwidth

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55
Q

Recently introduced technique that uses this ability— lower frequency ultrasound is transmitted into the patient, and the higher frequency harmonics, created from the interaction with contrast agents and tissues, are received as echoes

A

Harmonic imaging

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56
Q

Typically, how many individual rectangular elements comprise the transducer assembly

A

128 to 512

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57
Q

Linear array transducers typically contain how many elements

A

256 to 512

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58
Q

Largest transducer assemblies

A

Linear arrays

59
Q

Usually comprised of 64-128 individual elements in a smaller package than a linear array transducer

A

Phased arrays

60
Q

Its basic element is a capacitor cell, with a fixed electrode (backplate) and a free electrode (membrane). The principle of operatjon is electrostatic transduction

A

Capacitive micromachined ultrasonic transducers

61
Q

An alternating voltage is applied between the membrane and the backplate, and the modulation of the electrostatic force results in membrane vibration with the generation of ultrasound

A

Electrostatic transduction

62
Q

Its main advantage is better acoustic matching with propagation medium, which allows wider bandwidth capabilities, improved resolution

A

Capacitative micromachined ultrasonic transducers

63
Q

Slightly converging beam out to a distance determined by geometry and frequency of the transducer

A

Near field

64
Q

Diverging beam beyond the point

A

Far field

65
Q

Also known as the fresnel zone, is adjacent to the transducer face and has a converging beam profile

A

Near field

66
Q

Describes a large transducer surface as an infinite number of point sources of sound energy where each point is characterised as a radial emitter

A

Huygen’s principle

67
Q

Near field distance is increased, as the physical diameter and operation frequency of the transducer are increased or decreased?

A

Increased

68
Q

Peak ultrasound pressure happens in the

A

At the end of the near field

69
Q

Also known as the fraunhofer zone, and is where the beam diverges

A

Far field

70
Q

Less beam divergence occurs with ____ frequency, ____ diameter transducers

A

High frequency

Large diameter

71
Q

Method to rephase the signals by dynamically introducing electronic delays as function of depth (time)

A

Dynamic receive focusing

72
Q

At shallow/deep depths, rephasing delays between adjacent transducer elements are greatest

A

Shallow

73
Q

Process that increases the number of active receiving elements in the array with reflector depth, so that the lateral resolution does nor degrade with depth of propagation

A

Dynamic aperture

74
Q

Unwanted emissions of ultrasound energy directed away from the main pulse, caused by the radial expansion and contraction of the transducer element during thickness contraction and expansion

A

Side lobes

75
Q

How to reduce side lobes

A

Keep the individual transducer element widths small (less than 1/2 wavelength), reduce amplitude if peripheral transducer element excitations relative to the central element excitations

76
Q

Results when ultrasound energy us emitted far off-axis by multi-element arrays and are a consequence of the noncontinuous transducer surface of the discrete elements

A

Grating lobes

77
Q

Direction of side lobes

A

Forward directed

78
Q

Characteristics of grating lobes

A

Emitted from the array surface at very large angles

79
Q

Major factor that limits the spatial resolution and visibility of detail is the

A

Volume of acoustic pulse

80
Q

Dimensions that determine the minimal volume element

A

Axial, lateral, elevational (slice-thickness)

81
Q

Refers to ability to discern two closely spaced objects in the direction of the beam

A

Axial

82
Q

Also known as linear, range, longitudinal or depth resolution

A

Axial resolution

83
Q

The minimal required separation distance between two reflectors is

A

1/2 of SPL

84
Q

Number of cycles emitted per pulse by the transducer multiplied by the wavelength

A

SPL

85
Q

Also known as azimuthal resolution, refers to the ability to discern as separate two closely spaced objects perpendicular to the beam direction

A

Lateral resolution

86
Q

Best lateral resolution occurs at the

A

Near field-far field interface

87
Q

The elevational or slice-thickness dimension of ultrasound beam is ______ to the image plane

A

Perpendicular

88
Q

Weakest measure of resolution of array transducers

A

Slice thickness

89
Q

Have the ability to steer and focus the beam in the elevational dimension

A

1.5 D transducer arrays

90
Q

Responsible for generating the electronic delays for individual transducer elements in an array to achieve transmit and receive focusing and in phased arrays, beam steering

A

Beam former

91
Q

Provides the electrical voltage for exciting the piezoelectric transducer elements and controls the output transmit power by adjustment of applied voltage

A

Pulser

92
Q

It is synchronized with the pulser, isolates the high voltage associated with pulsing (~150 V) from the sensitive amplification stages during receive mode, with induced voltages ranging from approximately 1 to 2 uV from returning echoes

A

Transmit/receive switch

93
Q

In this transducer operation, the ultrasound beam is intermittently transmitted, with a majority of time occupied by listening for echoes

A

Pulse-echo mode

94
Q

Number of times the transducer is pulsed per second is known as the

A

pulse repetition frequency (PRF)

95
Q

For imaging, PRF range from

A

2000 to 4000 pulses per second (2-4 kHz)

96
Q

Time between pulse is the

A

Pulse repetition period

97
Q

Ratio of number of cycles in the pulse to the transducer frequency and is equal to the instantaneous “on” time

A

Pulse duration

98
Q

The fraction of “on” time, is equal to the pulse duration divided by the PRP

A

duty cycle

99
Q

User adjustable amplification of the returning echo signals as a function of time, to further compensate for beam attenuation

A

Time varied gain, depth gain compensation and swept gain (TGC)

100
Q

Effectively reduces the maximum to minimum range of echo voltages as a function of time to approximately 50dB

A

TGC amplification

101
Q

Feature of some broadband receivers that changes the sensitivity of the tuner bandwidth with time, so that echoes from shallow depths are tuned to a higher frequency range, while echoes from deeper structures are tuned to lower frequencies

A

Dynamic frequency tuning

102
Q

Defines the effective operational range of an electronic device from the threshold signal level to the saturation level

A

Dynamic range

103
Q

Inverts the negative amplitude signals of the echo to positive values

A

Rectification

104
Q

Convert the rectified amplitudes of echo into smoothed, single pulse

A

Demodulation and envelope detection

105
Q

Display of the processed information from the receiver versus time. This is currently used in ophthalmology applications for precise distance measurements of the eye

A

A mode (amplitude)

106
Q

Electronic conversion of the A-mode and A-line information into brightness-modulated dots along the A-line trajectory

A

B-mode (brightness)

107
Q

Technique that uses B-mode information to display the echoes from a moving organ, such as the myocardium and valve leaflets, from a fixed transducer position and beam direction on the patient

A

M-mode (motion)

108
Q

Method in which ultrasound information is obtained from several different angles of insonation and combined to produce a single image

A

Spatial compounding

109
Q

Based on shift of frequency in an ultrasound wave caused by a moving reflector, such as blood cells in the vasculature

A

Doppler ultrasound

110
Q

Difference between the incident frequency and reflected frequency

A

Doppler shift

111
Q

Refers to vector quantity describing both the distance travelled per unit time (speed) and the direction of movement such as blood flow

A

Velocity

112
Q

Preferred Doppler angle ranges from

A

30- 60 degrees

113
Q

In this angle, doppler shift is small, and minor errors in angle accuracy can result in large errors in velocity

A

More than 60 degrees

114
Q

At this doppler angle, refraction and critical angle interactions can cause problems, as can aliasing of the signal in pulsed Doppler studies

A

Less than 20 degrees

115
Q

Simplest and least expensive device for measuring blood velocity

A

Continuous wave Doppler system

116
Q

A method of signal processing called _______ is phase sensitive and can indicate the direction of flow either toward or away from the transducers

A

Quadrature technique

117
Q

Combines the velocity determination of continuous wave Doppler systems and the range discrimination of pulse echo imaging

A

Pulse doppler ultrasound

118
Q

A signal can be reconstructed unambiguously as long as the true frequency is _______

A

Less than half the sampling rate

119
Q

Combination of 2D B-mode imaging and pulsed Doppler acquisition

A

Duplex scanning

120
Q

2D visual display of moving blood in the vasculature, superimposed upon the conventional gray-scale image

A

Color flow imaging

121
Q

Technique to measure the similarity of one scan line measurement to another when the maximum correlation (overlap) occurs

A

Phase-shift autocorrelation

122
Q

Alternate method for color flow imaging. It is based upon the measurement that a reflector has moved over time, between executive pulse echo acquisitions

A

Time domain correlation

123
Q

Direction of flow is best determined with a

A

Small Doppler angle (about 30 degrees)

124
Q

Error caused by an insufficient sampling rate (PRF) relative to the high frequency Doppler signals generated by fast-moving blood.

A

Aliasing

125
Q

Signal processing method that relies on the total strength of the Doppler signal (amplitude) and ignores directional (phase) information

A

Power doppler

126
Q

Artifacts seen un power doppler imaging which are related to color signals arising from moving tissues, patient motion or transducer motion

A

Flash artifacts

127
Q

Most common ultrasound contrast agents

A

Encapsulated microbubbles of 3-5 um diameter containing air, nitrogen or insoluble gaseous compounds such as perfluorocarbons, encapsulation materials such as human albumin

128
Q

Hypointense signal area distal to an object or interface and is caused by objects with high attenuation or reflection of the incident beam without the return of echoes

A

Shadowing

129
Q

Arise from multiple echoes generated between two closely spaced interfaces reflecting ultrasound energy back and forth during the acquisition of the signal and before the next pulse

A

Reverberation artifact

130
Q

These artifacts are often caused by reflections between a highly reflective interface and the transducer or between reflective interfaces such as metallic objects, calcified tissues or air pocket/partial liquid areas of anatomy

A

Reverberation

131
Q

Comet tail artifact is a form of

A

Reverberation artifact

132
Q

Arise from resonant vibrations within fluid trapped between tetrahedron of air bubbles, which creates a continuous sound wave that is transmitted back to the transducer and displayed as series of parallel bands extending posterior to a collection of gas

A

Ring-down artifacts

133
Q

Caused by the variability of speed of sound in different tissues

A

Speed displacement

134
Q

Created when a high PRF limits the amount of time spent listening for echoes during the PRP

A

Ambiguity

135
Q

Represented as a rapidly changing mixture of colors, typically seen distal to a strong reflector such as a calculus, and is often mistaken for an aneurysm when evaluating vessels

A

Twinkling artifact

136
Q

Determined with the first high-contrast target (positioned at several depths from 0- ~1cm) visible in the image

A

Dead zone depth

137
Q

Rate at which sound energy flows thru a unit area and is usually expressed in units of watts per square centimeter or milliwatts per square centimeter

A

Acoustic intensity

138
Q

Accepted method of determining power levels for real time instruments that provide the operator with quantitative estimates of power deposition in the patient

A

Thermal and mechanical indices of ultrasound operation

139
Q

Ratio of the acoustical power produced by the transducer to the power required to raise tissue in the beam area by 1 degree celsius

A

Thermal index

140
Q

Consequence of negative pressures (rarefaction of the mechanical wave) that induce bubble formation from the extraction of dissolved gas in the medium

A

Cavitation

141
Q

Value that estimates the likelihood of cavitation by ultrasound beam

A

Mechanical index

142
Q

It is directly proportional to the peak rarefaction (negative) pressure and inversely proportional to the square root of the ultrasound frequency

A

Mechanical index

143
Q

Generally refers to the pulsation (expansion and contraction) of persistent bubbles in the tissue that occur at low and intermediate ultrasound intensities

A

Stable cavitation

144
Q

At higher ultrasound intensity levels, ________ can occur, whereby the bubbles respond nonlinearly to the driving force, causing a collapse approaching the speed of sound

A

Transient cavitation

Physics (7 decks)

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