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Rad > ULTRASOUND COPY > Flashcards

ULTRASOUND COPY Flashcards

1
Q

mechanical energy that propagates thru a continuous elastic medium by the compression and rarefaction of particles

A

Sound

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2
Q

energy propagation occurs as a wavefront in the direction of energy travel

A

longitudinal wave

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3
Q

distance (mm) bet compressions and rarefactions or bet any 2 points that repeat on the sinusoidal wave of pressure amplitude

A

wavelength (λ)

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4
Q

of times the wave oscillates thru one cycle each second

A

frequency (f)

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5
Q

infrasound Hz

A

<15 Hz

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6
Q

Audible acoustic spectrume Hz

A

15-20kHz

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7
Q

Ultrasound Hz

A

> 20 kHz

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8
Q

Medical Ultrasound Hz

A

2-100 mHz

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9
Q

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

A

Reflection

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10
Q

describes the change in direction of the transmitted US energy w/ non perpendicular incidence

A

Refraction

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11
Q

occurs by reflection or refraction usually by small particles w/in the tissue medium

A

Scattering

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12
Q

gives rise to the characteristic texture and gray-scale in the image

A

Scattering

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13
Q

: loss of intensity of beam from absorption and scattering in the medium

A

Attenuation

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14
Q

process whereby acoustic energy is converted to heat energy –> sound energy is lost and cannot be recovered

A

Absortpion

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15
Q

Can be likened to the stiffness and flexibility of a compressible medium

A

Acoustic impedance (z)

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16
Q

Acoustic impedance (z) unit

A

Rayl

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17
Q

Large difference in acoustic impedance results to

A

Large Reflection

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18
Q

means for producing an image using pulse echo technique

A

Acoustic impedance (z)

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19
Q

Type of Transducer

converts electrical energy to mechanical energy by physical deformation of crystal structure

A

Piezoelectric materials

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20
Q

Type of Transducer

mechanical pressure applied to its surface creates electrical energy

A

Piezoelectric materials

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21
Q

Type of Transducer

characterized by a well defined molecular arrangement of electrical dipoles

A

Piezoelectric materials

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22
Q

molecular entities containing (+) and (-) electrical charge w/ overall neutral charge

A

Electric dipole

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23
Q

Piezoelectric materials are often mad of ?

A

PZT
Plumbum
Zicornate
Titanate

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24
Q

Type of Transducer

voltage is applied to PZT => PZT initially contract then subsequently vibrates at a natural resonance frequency

A

Resonance Transducer

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25
Q

higher frequencies are achieved w/ thinner/thicker? elements and lower frequencies w/ thinner/thicker? elements

A

high frequency - thinner

low frequency - thicker

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26
Q

layered on the back of the PZT and absorbs the backward directed US energy and attenuates stray US signals from the housing

A

Damping block

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27
Q

creates an US pulse w/ a short spatial pulse length necessary to preserve detail along the beam axis (axial resolution)

A

Damping block

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28
Q

bandwidth of sound from a transducer

A

Q factor

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29
Q

Q factor: narrow bandwidth, long SPL

A

High Q transducer

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30
Q

Q factor: broad bandwidth, short SPL

A

Low Q transducer

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31
Q

requires a relatively narrow band transducer response to preserve velocity information encoded by changes in the echo frequency relative to the incident frequency

A

Doppler

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32
Q

Provides the interface bet the raw transducer element and the tissue
Minimizes acoustic impedance difference bet the transducer and the patient
Consists of layers of materials w/ acoustic impedance intermediate to soft tissue and transducer material

A

Matching layer

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33
Q

is used to eliminate air pockets w/c could attenuate and reflect sound beam

A

Acoustic coupling gel (acoustic impedance is similar to soft tissue)

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34
Q

Center of frequency can be adjusted in the transmit mode
Piezo element is machined into a large # of small rods and filled w/epoxy resin for smooth surface
Provides greater transmission efficiency w/o multiple matching layers because its acoustic properties are closer to tissue

A

Non-resonance (broad bandwidth) multifrequency transducer

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35
Q

Sound pulse can be produced at low frequency and echoes received at higher frequency

A

HARMONIC IMAGING

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36
Q

Greater depth of penetration
Noise and clutter removal
Improved lateral spatial resolution

A

Native tissue harmonic imaging

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37
Q

Rectangular FOV is produced

A

Linear arrays

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38
Q

trapezoidal FOV is produced

A

Curvilinear array

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39
Q

occurs by firing another group of transducer elements

A

Subsequent A line acquisition

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40
Q

Echoes are detected in the receive mode by acquiring signals from most of the transducer elements

A

Linear arrays

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41
Q

Simultaneous firing of approx 20 adjacent elements produce the beam  adjacent elements produce a synthetic aperture

A

Linear arrays

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42
Q

256-512 elements – largest

A

Linear arrays

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43
Q

64-128 elements – smaller

A

Phased arrays

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44
Q

All elements are activated nearly simultaneously to produce a single beam

A

Phased arrays

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45
Q

Beam can be steered electronically w/o physically moving the transducer

A

Phased arrays

46
Q

All elements detect the returning echoes

A

Phased arrays

47
Q

US beams exhibit 2 distinct patterns:

A

Near field

Far field

48
Q

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

A

Near field

49
Q

Fresnel zone

A

Near field

50
Q

Converging

A

Near field

51
Q

Occurs due to multiple constructive/destructive interference patterns of US waves from the transducer surface  causes the beam profile to be tightly collimated

A

Near field

52
Q

Near field length is dependent on

A

Transducer diameter
Propagation wavelength (thus, frequency)
NFL increases if frequency and diameter are increased

53
Q

NFL (near field length) increases if __ and __ are increased

A

frequency and diameter

54
Q

NEAR FIELD

___ is dependent on the beam diameter and is best at the end of the near field for a single element transducer

A

Lateral resolution

55
Q

Ability of the system to resolve objects in a direction perpendicular to the beam direction
Poor in areas close to and far from the transducer surface

A

Lateral resolution

56
Q

occurs at the end of the near field

A

Peak US pressure

57
Q

Beam is divergent

A

Far Field

58
Q

Fraunhofer zone

A

Far field

59
Q

US intensity decreases monotonically with distance

A

Far field

60
Q

the major factor that limits spatial resolution and visibility of detail is the volume of the acoustic pulse

A

Spatial resolution

61
Q

Linear, range, longitudinal or depth resolution

A

Axial resolution

62
Q

Ability to discern 2 closely spaced objects in the direction of the beam
Requires that returning echoes be distinct without overlapping

A

Axial resolution

63
Q

aka azimuthal resolution

A

Lateral resolution

64
Q

Ability to discern as separate 2 closely spaced objects perpendicular to beam direction

A

Lateral Resolution

65
Q

Determines lateral resolution

A

Beam diamter

66
Q

Depth dependent resolution

A

Lateral resolution

67
Q

Far field, beam diverges  substantially reduced ____ resolution

A

Lateral resolution

68
Q

____ –> improved overall in focus lateral resolution w/ depth –> decrease frame rate

A

increase # of focal zone

69
Q

Resolution perpendicular to image plane

A

Elevational resolution

70
Q

dependent on transducer element height

A

Elevational resolution

71
Q

Display of processed info from the receiver vs time

A

A mode

72
Q

Seldom used (ophtha applications for precise distance measurements of the eye)

A

A mode

73
Q

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

A

B mode

74
Q

Brightness of dot is proportional to echo signal amplitude

Used for M mode and 2D gray scale imaging

A

B mode

75
Q

Uses B mode info to display echoes from a moving organ

A

M mode

76
Q

Provides excellent temporal resolution of motion patterns

A

M mode

77
Q

difference between incident and reflected frequency

A

Doppler shift

78
Q

Proportional to velocity of the blood cells

A

Doppler shift

79
Q

angle bet direction of blood flow and direction of sound

A

Doppler angle

80
Q

Without correction, Doppler shift will be less and there will be an underestimate of ___

A

blood velocity

81
Q

Doppler Angle: measured Doppler frequency is ½ the actual

A

> 60 degrees

82
Q

Doppler angle: measured frequency is 0

A

At 90 degrees

83
Q

preferred doppler angle

A

30-60 degrees

84
Q

apparent Doppler shift is small

A

> 60 degrees

85
Q

Doppler angle

refraction and critical angle interactions can cause problems as can aliasing

A

< 20 degrees

86
Q

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

A

Color flow imaging

87
Q

determines the processing time necessary to evaluate the color flow data

A

FOV

88
Q

Smaller/bigger? FOV delivers a faster frame rate but sacrifices area evaluated

A

smaller

89
Q

Error caused by insufficient sampling rate relative to the high frequency Doppler signals generated by fast moving blood

A

Velocity aliasing

90
Q

How to eliminate velocity aliasing?

A

Adjust the velocity scale to a wider range

91
Q

wraps around to negative amplitude masquerading a reversed flow

A

Velocity aliasing

92
Q

Relies on the total strength of the Doppler signal (amplitude)
Ignores directional information
Dependent on amplitude of Doppler regardless of frequency shift
Improves sensitivity to motion at the expense of directional and quantitative information
Not dependent as much to Doppler angle
Aliasing is not a problem
Allows detection of very subtle low blood flow
Slower frame rates
Significant amount of flash artifacts from moving tissue, pt motion or transducer motion

A

Power doppler

93
Q

Arise from the incorrect display of anatomy or noise during imaging

A

Artifacts

94
Q

Hypointense signal area distal to an object or interface

A

Shadowing

95
Q

Caused by objects w/ high attenuation or reflection of the incident beam  no return of echoes

A

Shadowing

96
Q

Highly attenuating objects (bone/kidney stone) can induce low intensity streaks in the image

A

Shadowing

97
Q

Occurs distal to objects having very low US attenuation

A

Enhancement

98
Q

Hyperintense signals arise from increased transmission of sound by these structures

A

Enhancement

99
Q

Arise from multiple echoes generated bet 2 closely spaced interfaces reflecting US energy back and forth during acquisition of the signal and before the next pulse

A

Reverberation

100
Q

Often caused by reflections bet a highly reflective interface and the transducer or bet reflective interface such as metallic objects, calcified tissues or air pockets

A

Reverberation

101
Q

Typically manifested as multiple equally spaced boundaries w/ decreasing amplitude along a straight line from the transducer

A

Reverberation

102
Q

Arise from resonant vibrations w/in fluid trapped bet a tetrahedron of air bubbles => creates a continuous sound wave that is transmitted back to the transducer => displayed as a series of parallel bands extending posterior to a collection of gas

A

Ring down artifact

103
Q

The echoes bounce back and forth between the two

boundaries and produce equally spaced signals of diminishing amplitude in the image

A

Comet tail artifact

104
Q

Artifact represented by a rapidly changing mixture of colors

A

Twinkling

105
Q

Artifact typically seen distal to a strong reflector (calculus)

A

Twinkling

106
Q

Artifact possibly due to echoes from the strong reflector w/ frequency changes due to wide bandwidth of the initial pulse and narrow band ringing caused by the structure

A

Twinkling

107
Q

highest instantaneous intensity in the beam

A

Temporal peak

108
Q

time averaged intensity over the PRP

A

Temporal average

109
Q

highest intensity spatially in the beam

A

Spatial peak

110
Q

good indicator of thermal US effects

A

Spatial peak-temporal average intensity

111
Q

Indicator of potential mechanical bioeffects and cavitation

A

Spatial peak-pulse average intensity

112
Q

the accepted methods of determining power levels

A

Thermal index (TI) and mechanical index (MI)

Rad (10 decks)

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