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FEESICKS BUSHBIRD III > ***Chapter 14 - Ultrasound > Flashcards

***Chapter 14 - Ultrasound Flashcards

1
Q

Transmitter and receiver of ultrasound pulses

A

Transducer array

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2
Q

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

A

Sound

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3
Q

Energy propagation occurs as a wave front in the direction of energy travel

A

Longitudinal wave

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4
Q

Expressed in mm or um; 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

The number of times the waves oscillates through one cycle each second

A

Frequency

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6
Q

Sound waves with frequencies less than 15 cycles per second (Hz)

A

Infrasound

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7
Q

Comprises the range between 15 Hz and 20kHz

A

Audible acoustic spectrum

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8
Q

Represents the frequency range above 20kHz

A

Ultrasound

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9
Q

Uses frequencies in the range of 2 to 10 MHz,with specialized ultrasound applications up to 50 MHz

A

Medical ultrasound

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10
Q

Time duration of one wave cycle

A

Period

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11
Q

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

A

Speed of sound

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12
Q

Determined by the ratio of the bulk modulus and the density of the medium

A

Wave speed

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13
Q

A highly compressible medium such as AIR, has a ____speed of sound

A

Low

*while a less compressible medium(e.g.bone),has a higher speed of sound

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14
Q

A less dense medium (e.g.dry air) has a ______ speed of sound than a denser medium (e.g.humid air)

A

Higher

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15
Q

Average speed of sound for:
A. Soft tissue
B. Fatty tissue
C. Air

A

A. 1,540 m/s
B. 1,450 m/s
C. 330 m/s

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16
Q

Fundamental property that generates echoes in an ultrasound image

A

Difference on the speed of sound at tissue boundaries

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17
Q

Higher frequency sound has _____ wavelength

A

SHORTER

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18
Q

Spatial resolution of the ultrasound image depend on the ____

A

Wavelength

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19
Q

Attenuation of the ultrasound sound beam energy depend on the _______

A

Frequency

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20
Q

High frequency utz beam (small wavelength) provides _____ resolution and image detail than a lower frequency beam

A

Better

*the depth of the beam penetration is significantly reduced at higher frequency

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21
Q

Position of the periodic wave with respect to a reference point

A

Phase

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22
Q

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

A

Pressure amplitude

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23
Q

SI unit of pressure; defined as one Newton per square meter (N/m2)

A

Pascal (Pa)

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24
Q

Occur with two utz waves of the same frequency and phase, resulting in a higher amplitude output wave

A

Constructive interference

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25
Q

Occurs with the waves 180 degrees out-of-phase, resulting in a lower amplitude output wave

A

Destructive interference

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26
Q

Occurs when waves of slightly different frequency interact, resulting in an output waveform of higher and lower amplitude

A

Complex interference

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27
Q

Amount of power (energy per unit time) per unit area

A

Intensity,I

*described in milliwatts/cm2

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28
Q

Relative intensity and pressure levels described as a logarithmic ratio

A

Decibel (dB)

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29
Q

When the intensity ratio is >1 the dB values are _____;

When the intensity ratio is <1 the dB values are ____

A

Positive; negative

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30
Q

The tissue thickness that reduces the ultrasound intensity by 3 dB is considered the _____

A

Half-value thickness (HVT)

*a loss of 3 dB (-3 dB) represents a 50% loss of signal intensity

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31
Q

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

A

Reflection

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32
Q

Describes the change in direction of the transmitted ultrasound energy with nonperpendicular incidence

A

Refraction

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33
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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34
Q

Loss of intensity of the utz beam from absorption and scattering in the medium;

Loss of acoustic energy with distance traveled

A

Attenuation

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35
Q

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

A

Absorption

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36
Q

Likened to the stiffness and flexibility of a compressible medium
Density X speed of sound; SI Unit is kg/m2s,
rayl(special name).

*one rayl is equal to 1 kg/(m2s)

A

Acoustic impedance

*gives rise to difference is transmission and reflection of ultrasound energy

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37
Q

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

A

Reflection coefficient

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38
Q

Defined as the fraction of the incident intensity that is transmitted across an interface

A

Intensity transmission coefficient

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39
Q

A conduit of tissue that allows ultrasound transmission through structures such as the lung is known as an _____

A

Acoustic window

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40
Q

A smooth 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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41
Q

Terms used for describing the scatter characteristics relative to the average background signal

A

Hyperechoic (higher scatter amplitude);

Hypoechoic (lower scatter amplitude)

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42
Q

2 chief causes of attenuation

A
  1. Scattering

2. Tissue absorption of the incident beam

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43
Q

The relative intensity loss per centimeter of travel for a given medium

A

Attenuation coefficient

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44
Q

An approx. rule of thumb for soft tissues…

A
  1. 5 dB per cm per MHz OR

0. 5 (dB/cm)/MHz

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45
Q

Utz attenuation occur ____ with penetration depth and

____ with increased frequency

A

Exponentially; increases

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46
Q

Functional component of the transducer

A

Piezoelectric material (often a crystal or ceramic)

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47
Q

Molecular entities containing positive and negative electrical charges that have an overall neutral charge

A

Electrical dipoles

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48
Q

Natural piezoelectric material

A

Quartz crystal

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49
Q

Synthetic piezoelectric ceramic

A

Lead-zirconate-titanate(PZT)

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50
Q

Low frequency oscillation is produced with a _____ piezoelectric element

A

Thicker

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51
Q

Layered on the back of the piezoelectric element, absorbs the backward directed ultrasound energy and attenuates stray ultrasound signals from the housing; also dampens the transducer vibration

A

Damping block

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52
Q

Lessens the purity of the resonance frequency and introduces a broadband frequency spectrum

A

Dampening of the vibration (also known as “ring-down”)

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53
Q

Describes the bandwidth of the sound emanating from the transducer

A

Q factor

  • high Q transducer-narrow bandwidth,long SPL
  • caused by light damping
  • low Q transducer-wide bandwidth,short SPL
  • caused by heavy damping
54
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

55
Q

Transducers which contain 256 to 512 elements; physically these are the largest transducer assemblies
-produces a beam by firing a subset of the total number of transducer elements as a group

A

Linear arrays

  • produces a rectangular field of view(FOV)
  • for a curvilinear array, a trapezoidal FOV is produced
56
Q

Produces a beam from ALL of the transducer elements fired with fractional time delays in order to steer and focus the beam

A

Phased array transducer

57
Q

CMUT

  • principle of operation: electrostatic transduction
  • basic element of a CMUT: a capacitor cell with a fixed electrode (backplate) and a free electrode (membrane)
A

Capacitive Micromachined Ultrasonic transducers

58
Q

UTZ beam pattern that is adjacent to the transducer face and has a converging beam profile

A

Near field (Fresnel Zone)

59
Q

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

A

Huygen principle

60
Q

Near field length is dependent on (2):

A

Transducer diameter and propagation wavelength

61
Q

The ability of the system to resolve objects in a direction perpendicular to the beam direction

A

Lateral resolution

62
Q

Where the ultrasound beam diverges…

A

Far field (Fraunhofer zone)

63
Q

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

A

Dynamic receive focusing

64
Q

A process which increases the number of active receiving elements in the array with reflector depth, so that the lateral resolution does not degrade with depth of propagation

A

Dynamic aperture

65
Q

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

A

Side lobes

66
Q

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

A

Grating lobes

67
Q

Off-axis energy emissions produced by linear and phased array transducers (2)

A

Side lobes (are forward directed)

Grating lobes (emitted from the array surface at very large angles)

68
Q

(In UTZ), the major factor that limits spatial resolution and visibility of detail…

A

Volume of the acoustic pulse

69
Q

Determines the minimal volume element in UTZ (3)

A

Axial, lateral and elevational(slice thickness) dimensions

70
Q

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

A

Axial resolution (aka linear, range, longitudinal or depth resolution)

71
Q

The number of cycles emitted per pulse by the transducer multiplied by the wavelength

A

Spatial pulse length (SPL)

72
Q

Refers to the ability to discern as separate two closely spaced objects perpendicular to the beam direction

A

Lateral resolution (aka Azimuthal resolution)

73
Q

The best lateral resolution occurs at the ______

A

Near field-far field interface

74
Q

Dimension of the ultrasound beam that is perpendicular to the image plane

A

Elevational or slice-thickness dimension

75
Q

Typically the weakest measure of resolution for array transducers

A

Slice thickness

76
Q

Multiple linear array transducers with five to seven rows; have the ability to steer and focus the beam in the elevational dimension

A

1.5 D transducer arrays

77
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

78
Q

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

A

Pulser (aka the transmitter)

79
Q

(In digital beam former systems),a ______ determines the amplitude of the voltage

A

Digital-to-analog converter (DAC)

80
Q

Isolates the high voltage associated with pulsing (150 V) from the sensitive amplification stages during receive mode

A

Transmit/receive switch

81
Q

The ultrasound beam is intermittently transmitted, with a majority of the time occupied by listening for echoes

A

Pulse-echo mode of transducer operation

82
Q

Event where the ultrasound pulse is created with a short voltage waveform provided by the pulser of the ultrasound system

A

Main bang

83
Q

Number of times the transducer is pulsed per second

A

Pulse repetition frequency (PRF)

84
Q

The time between pulses; equal to the inverse of the PRF (pulse repetition frequency)

A

Pulse repetition period (PRP)

85
Q

Determined from the product of the speed of sound and the PRP divided by 2

A

Maximal range

86
Q

A. UTZ frequency is calibrated in ____

B. UTZ period is measured in _____

A

A. MHz

B. microseconds

87
Q

A. PULSE REPETITION FREQUENCY (PRF) is calibrated in ___

B. PULSE REPETITION PERIOD (PRP) is measured in ____

A

A. kHz

B. milliseconds

88
Q

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

A

Pulse Duration

89
Q

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

A

Duty cycle

90
Q

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

A

Dynamic frequency tuning

91
Q

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

A

TGC (aka time varied gain, depth gain compensation, swept gain)

92
Q

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

A

Dynamic range

93
Q

Increases the smallest echo amplitudes and decreases the largest amplitudes

A

Logarithmic amplification

94
Q

Inverts the negative amplitude signals of the echo to positive values

A

Rectification

95
Q

Convert the rectified amplitudes of the echo into a smoothed single pulse

A

Demodulation and enveloped detection

96
Q

______ level adjustment sets the threshold of signal amplitudes allowed to pass to the digitization and display subsystems

A

Rejection

97
Q

2 RECEIVER subsequent signal processing steps that the operator can control …

A
  1. TGC

2. Noise/clutter rejection

98
Q

Display of the processed information from the receiver versus time (after the receiver processing steps)

A

A-mode (A for amplitude)

*A-mode and A-line info is currently used in OPHTHA applications for precise distance measurements of the eye

99
Q

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

A

B-Mode (B for Brightness)

  • used for M-mode and 2D gray-scale imaging
100
Q

A 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 (M for motion)

101
Q

Used to create 2D images from echo info from distinct beam directions and to perform scan conversion to enable image data to be viewed on video display monitors

A

Scan converter

102
Q

UTZ spatial resolution has components in three directions, namely…

A

Axial, lateral and elevational

103
Q

UTZ resolution type determined by the frequency of the UTZ and the damping factor of the transducer

A

Axial resolution

104
Q

UTZ resolution types determined by the dimensions (width and height,respectively) of the transducer aperture, the depth of the object, and mechanical and electronic focusing

A

Lateral and elevational resolutions

105
Q

A change in the transmitted UTZ pulse directional boundary with nonperpendicular distance;

Misplaced anatomy often occurs in the image during the scan

A

Refraction

106
Q

A hypointense signal area distal to an object or interface and is caused by objects with high attenuation or reflection of the incident beam w/o the return of echoes

A

Shadowing

107
Q

Occurs distal to objects having very low UTZ attenuation

A

Enhancement

108
Q

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

A

Reverberation

*typically manifested as multiple,equally spaced boundaries with decreasing amplitude along a straight line from the transducer

109
Q

A form of reverberation

A

Comet tail artifact

110
Q

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

A

Ring-down artifacts

111
Q

Caused by the variability of speed of sound in different tissues

A

Speed displacement

112
Q

Emissions of the UTZ energy that occur in a direction slightly off-axis from the main beam and arise from the expansion of the piezoelectric elements orthogonal to the main beam

A

Side lobes

113
Q

Occur with multielement array transducers and result from the division of a smooth transducer surface into a large number of small elements

A

Grating lobes

114
Q

***page 567

A

Multipath reflection and mirror image

115
Q

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

A

Ambiguity artifacts

116
Q

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

A

Twinkling artifact

*possibly due to echoes from a strong reflector with frequency changes due to wide bandwidth of the initial pulse and the narrow band “ringing” caused by the structure

117
Q

Determined by the beam width of the transducer array perpendicular to the image plane and is greater than the beam width in the image plane

A

Slice thickness

118
Q

Rate of energy production, absorption or flow

A

Power

*SI unit: watt(W) - one joule of energy per second

119
Q

Rate at which sound energy flows thru a unit area and is usually expressed in units of watts per square centimeter (W/cm2) or milliwatts per square centimeter (mW/cm2)

A

Acoustic intensity

120
Q

A device containing a small piezoelectric element coupled to external conductors and mounted in a protective housing; measures UTZ pressure amplitude within a beam

A

Hydrophone

121
Q

Highest instantaneous intensity in the beam

A

Temporal peak

122
Q

Time-averaged intensity over the PRP

A

Temporal average

123
Q

Average intensity of the pulse

A

Pulse average

124
Q

Highest intensity spatially in the beam

A

Spatial peak

125
Q

Average intensity over the beam area, usually taken to be the area of the transducer

A

Spatial average

126
Q

The acoustic power contained in the UTZ beam, averaged over at least one PRP and divided by the beam area

A

Spatial average-temporal average intensity(I sata)

127
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 (TI)

128
Q

A consequence of the negative pressures that induce bubble formation from the extraction of dissolved gases in the medium

A

Cavitation

129
Q

A value that estimates the likelihood of cavitation by ultrasound beam

A

Mechanical index (MI)

130
Q

Best indicator of heat deposition (2)

A
  1. I spta

2. Calculated TI value

131
Q

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

A

Stable cavitation

132
Q

Occurs at higher UTZ intensity levels, where the bubble respond linearly to the driving force, causing a collapse approaching the speed of sound. At this point, the bubbles might dissolve, disintegrate or rebound

A

Transient cavitation

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