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CMI 350 > Ch.12 Two-Dimensional Imaging > Flashcards

Ch.12 Two-Dimensional Imaging Flashcards

1
Q

Mechanical Transducer

A

contains a single, circular, disc-shaped active element that is physically moved. This movement creates a scan plane

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2
Q

Mechanical Transducer
Crystals: # and shape

A

can have only 1 active element ; coin shape

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3
Q

What image shape do mechanical transducers make?

A

fan or sector shaped; crystal is physically moved. (Car wind shield wiper sweep)

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4
Q

Mechanical Transducer:
Beam steering
Beam focusing

A

Mechanical steering
-2D image is built up by rotating the crystal with a motor.
Fixed focal depth called:
conventional, mechanical, or fixed focusing

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5
Q

What are the two methods of fixed focusing?

A

Internal focusing: the use of a curved active element.
External focusing: the use of an acoustic lens.

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6
Q

Focusing occurs in what planes?

A

Both the horizontal and vertical planes bc of the hour glass shape of the sound beam.

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7
Q

Whenever the crystal in any single crystal transducer breaks, the ______ image is ______ .

A

entire
lost

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8
Q

Transducer Arrays

A

contain multiple active elements.
-comprise a single slab of PZT cut into a collection of separate pieces called elements

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9
Q

Each active element is connected by a _____ to its own _______ _______ in the ultrasound system.

A

wire
electric circuitry

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10
Q

Channel

A

is the combination of the active element, wire, and system electronics

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11
Q

Each element has its own electric connection, the system can excite a ______ or _______ _________ in various ways during ___________ .

A

single or multiple elements
transmission

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12
Q

During reception, each individual crystal produces a ________ ________ ________ that returns to the system’s receiver.

A

small electronic signal

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13
Q

What are the types of array transducers?

A

Linear
Annular
Convex

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14
Q

Linear transducer arrangement

A

active elements are arranged in a straight line

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15
Q

Annular transducer arrangement

A

elements are arranged as circular rings with a common center

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16
Q

Convex transducer arrangement

A

Active elements are arranged in a bowed or arched line. The transducer may also be called a curved, or curvilinear array.

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17
Q

Phasing

A

is when the beam is steered and focused using an electrical technique

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18
Q

Linear Phased Array Transducers is a

A

small square or rectangular transducer about 1 cm on each side that has no moving parts. (carotid one)

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19
Q

Linear Phased Array:
Crystal # & Shape

A

as many as 100 to 300 elements arranged along the face of the probe.

Placed side by side, each element is rectangular and narrow with a width of 1/4th to 1/2 of the sound’s wavelength.

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20
Q

Linear Phased Array:
image shape

A

fan or sector-shaped similar to mechanical transducer

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21
Q

Linear Phased Array:
Beam Steering

A

2D image is built up with an electronic steering process called phasing ; no moving parts
(wind shield wiper sweep motion)

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22
Q

Phased array ALWAYS means:

A

adjustable or multi-focus

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23
Q

Linear Phased Array:
Beam Focusing

A

focused electronically

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24
Q

Unlike mechanical transducers with a single fixed focus, the phased array system has controls that allow the sonographer to ______ the ______ and amount of ________ of the sound beam.

A

modify
depth
focusing

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25
Q

What is the advantage of phased array systems?

A

is the availability of electronically controlled, adjustable focusing.

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26
Q

Multi-focusing

A

phased array systems can transmit multiple beams down the same scan line, each with a different focal depth

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27
Q

Damage to one of the elements of a phased array transducer results in

A

inconsistent or erratic beam steering and focusing

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28
Q

How many elements in a phased array probe are used to create a single sound pulse?

A

all the active elements in a linear phased array probe are fired to create each sound pulse.
Ex: if 128 elements are present then 128 wavelets are created

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29
Q

Phased array wavelets interfere

A

constructively and destructively creating a single sound pulse.
The overall pattern of the signals determine the sound beam’s direction and focus

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30
Q

The sound beam is steered if the

A

spike line has a slope

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31
Q

Beam former

A

the electronics within the ultrasound system that create the electrical patterns of travel

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32
Q

When a spike pattern is a straight line, an

A

unfocused sound beam is created

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33
Q

How does the pattern of the electrical spikes from the beam former focus the sound beam during transmission?

A

curved narrow pattern creates a focused sound beam during transmission.
outer crystals are excited earlier than inner

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34
Q

The sound beam is focused if the spike pattern is _________ .

A

curved

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35
Q

The sound beam created by a more curved electrical pattern will have a

A

shallower focus; however, the sound beam will still be directed straight down

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36
Q

Linear phased array:
Electronic Pattern -> Sound beam
Slope
Curvature

A

Sound beam:
steering
transmit focusing

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37
Q

How does a phased array system create images with multiple transmit foci?

A

to create an image with multiple transmit foci at different depths, the ultrasound system must send multiple sound beams down each scan line

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38
Q

Annular Phased Arrays

A

active elements of annular array transducers appear disc-like. The disc comprises multiple ring-shaped elements with a common center.
Appears like a rings on a bull’s eye

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39
Q

Annular Phased Array:
Beam Steering

A

Mechanical steering
(electrical not possible with annular arrays)

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40
Q

What is mechanical steering?

A

A motor physically moves the ringed-element array so that the sound beams are transmitted in different directions.

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41
Q

Annular Phased Array:
Beam Focusing

A

Multiple Transmit focal zones (Advantage)

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42
Q

How is data collected with annular phased array transducers?

A

Information is gathered and stored from a series of 4 different rings. The inner rings collect data from shallow depths. The outer rings collect data from deeper regions. Info is stored only from the respective focal zone’s of each ring.

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43
Q

Annular Phased Array transducers:
Image shape

A

fan or sector shaped

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44
Q

What happens when one ring of an annular array transducer malfunctions?

A

Only a portion of the image is lost. This will appear as a horizontal or side-to-side band of dropout at a particular depth depending on which ring.

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45
Q

What kind of images and acoustic footprint do linear sequential arrays create?

A

large acoustic footprints and rectangular images

46
Q

Linear sequential array transducer:
Crystal number and shape

A

120-250 rectangular shaped stripes of PZT arranged side by side in a line

47
Q

The active elements in linear sequential arrays are much _______ than those found in linear _____ arrays.

A

larger
phased

48
Q

Linear Sequential Array:
Beam Steering

A

a small group of the crystals are fired simultaneously to create each sound beam. They are parallel to each other and are typically directed straight ahead.

49
Q

Linear Sequential Arrays:
Beam focusing

A

in modern linear s. arrays focusing is achieved electronically. They perform both transmit and receive focusing using electronic phase delays.

50
Q

Electronic transmit focusing is achieved with a ?

A

curved excitation pattern of the active elements. The outer elements in the group of PZT crystals are fired earlier than the inner elements

51
Q

Receive focusing is achieved dynamically by

A

introducing electrical delays in the signals returning from the transducer. The phase delays change continuously during reception, thereby focusing the beam at many depths.

52
Q

Linear S. Array transducers:
image shape

A

rectangular image
(image is never wider than the transducer)

53
Q

When on element in a linear sequential array is damaged, only the

A

portion of the image extending directly below the damaged element is affected

54
Q

While using linear array transducers, why is it necessary to fire a group of crystals to produce a sound beam?

A

A sound beam created by the combination of wavelets from a small group of active elements is directional and well defined

55
Q

Why can’t a single crystal be used in a linear array?

A

a sound wave fired from a single element of a linear sequential array would have a Huygen’s V shaped wavelet. The beam would quickly diverge and result in poor lateral resolution.

56
Q

Can linear sequential array transducers steer sound beams electronically?

A

Yes, this form of steering creates a parallelogram shaped image rather than rectangular.

57
Q

_____-______ phase delays in the electrical excitation spikes of the elements steer the beam in linear sequential arrays.

A

Sloped-patterned.
(color doppler has no slope so it is a rectangular shaped image made by linear array, but the color doppler portion is a parallelogram bc electrical spike patterns create sound beams slopes

58
Q

To increase clinical utility of linear array probes, manufacturers have designed arrays with a

A

bowed or curved shape called convex, curved, or curvilinear

59
Q

Convex arrays;
number and shape

A

has 120 to 250 rectangular shaped strips of piezoelectric material arranged side by side in a bowed line (large array)

60
Q

The acoustic footprint may be as long as _ _ cm.
The active elements in a convex sequential array are ________ ___ ______ to a linear array, and much larger than those found in a _______ _______.

A

10
similar in size
phased array

61
Q

Convex transducers:
Beam Steering

A

some, but not all of the crystals are fired simultaneously to create each sound beam

62
Q

The sound beams transmitted from a convex array, unlike linear sequential arrays, are _____ _______ to each other.

A

not parallel

63
Q

Convex transducers:
Beam focusing

A

electronically

64
Q

Just like linear array probes, transmit focusing in convex elements in the fired group with a _______ ______ ______ pattern.

A

curved spike line

65
Q

Dynamic receive focusing

A

is achieved by introducing varying phase delays in the signals returning from the transducer to the ultrasound system during echo reception.

66
Q

Convex transducer:
image shape

A

blunted sector-shaped images

67
Q

Convex transducers rather than coming to a point in the ____ ____, the image appear to have a “bite” taken out of it.

A

near field

68
Q

The curvature at the top of the image of a convex transducer corresponds _______ to the ____of the convex array transducer.

A

directly
arc

69
Q

When one active element in a convex array is damaged, only the portion of the image ________ _______ the damaged element is affected.

A

directly below

70
Q

Vector array is

A

a combination of linear sequential and linear phased array technologies.

71
Q

Sloped phase delay patterns can electronically steer the sound beams in ________ ________.

A

different directions

72
Q

Vector arrays:
Number and shape of crystals

A

120 to 250 rectangular shaped strips of pzt elements arranged side by side in a line

73
Q

The footprint of the vector array may be ________, often only a few ____

A

small
cm

74
Q

Vector arrays:
Beam steering

A

vector arrays combines linear and phased array technology. Crystals are fired simultaneously to create a single sound beam. (like linear sequential)

75
Q

The electrical signals from the beam former are delayed in a _____ spike-line pattern as they excite a group of elements in a vector array.

A

sloped

76
Q

The beams radiate out in ________ ________ from the face of the transducer, this is similar to a _____ _____ transducers.

A

different directions
phased array

77
Q

Vector array:
Beam focusing

A

electronic focusing

78
Q

Vector array:
Similar to the phased array probes, both _______ focusing and ______ _______ focusing improve ________ resolution over a great range of depths.

A

transmit
dynamic receive
lateral

79
Q

Vector image shape

A

Trapezoidal
(Unlike phased or convex array images, the top of the vector image is flat

80
Q

Active Element Malfunction
Transducer type: Effect on image:
Mechanical

A

loss of entire image

81
Q

Active Element Malfunction
Transducer type: Effect on image:
Linear and Convex

A

dropout of image info from the top to the bottom of the image. The location of the line corresponds to the broken crystal

82
Q

Active Element Malfunction
Transducer type: Effect on image:
Phased array

A

Erratic steering and focusing. The extent to which the image is affected is variable

83
Q

Active Element Malfunction
Transducer type: Effect on image:
Annular Phased array

A

a horizontal or side-to-side band of dropout at a particular depth

84
Q

Mechanical:
image shape
steering technique
focusing technique

A

sector
mechanical
fixed

85
Q

Linear sequential
image shape
steering technique
focusing technique

A

rectangular
electronic
electronic

86
Q

Phased Array:
image shape
steering technique
focusing technique

A

sector
electronic
electronic

87
Q

Annular Phased:
image shape
steering technique
focusing technique

A

sector
mechanical
electronic

88
Q

Convex:
image shape
steering technique
focusing technique

A

blunted sector
electronic
electronic

89
Q

Vector:
image shape
steering technique
focusing technique

A

trapezoidal
electronic
electronic

90
Q

Slice Thickness or Elevational Resolution answers the question

A

are the reflections on the image created from structures directly in the imaging plane or from structures that lie above or beneath the imaging plane?

91
Q

Slice thickness is measured in

A

a direction perpendicular to the imaging plane or above-to-below the imaging plane

92
Q

The beam has a measurable thickness that can ______ with _______ .

A

vary
depth

93
Q

When the slice is thick, _____________ above and beneath the “assumed razor thin plane” create ______________ that appear in the image.

A

structures
reflections

94
Q

What shape of active element creates the best elevational resolution? Which transducer types have the best elevational resolution?

A

Disc-shaped crystals
mechanic and annular phased array transducers

95
Q

Active elements that are disc-shaped provide the __________ ultrasound ______ and the _____ elevational resolution within the ______ _____.

A

thinnest
slices
best
focal zone

96
Q

The width of the beam’s circular cross sectional area in one direction indicates the _________ (determining lateral resolution) and the height of the circle indicates the beam _________ (determining elevational resolution).

A

diameter
thickness

97
Q

What determines elevational resolution in phased array, linear array, and convex array transducers?

A

These array probes have rectangular shaped active elements placed side by side. With phasing, the beam is narrowed only side to side, but not above or below. This narrowing improves lateral resolution but does not affect slice thickness

98
Q

2-D array

A

contains thousands of elements arranged in a checkerboard pattern, creates 3D images

99
Q

4-D imaging

A

is real-time 3D imaging also uses 2-D array probes

100
Q

Rendering

A

creates an image from 3D data, constructs photo-like pictures with color, shadows, texture etc.

101
Q

Side lobes

A

additional areas of sound energy that extend outside of the main beam created by a single element transducer in the far zone, off-axis sound beams

102
Q

If side lobes are of sufficient intensity, structures within them can generate reflections that create _______ .

A

artifacts

103
Q

Reflections arising from within the side lobes degrade _________ __________ .

A

lateral resolution

104
Q

Grating lobes

A

similar to side lobes, but these are created by array transducers, beam’s main axis is stronger than these

105
Q

Why are grating lobes undesirable ?

A

they degrade lateral resolution
reduce image quality
create artifacts

106
Q

Transducers are designed to reduce the strength of side and grating lobes. How is this accomplished?

A

apodization

107
Q

What does the apodization process do?

A

alters the electrical spike voltages and reduce lobe strength

108
Q

Explain apodization

A

stronger electrical signals are used to excite the inner crystals, and progressively weaker electrical spikes excite the outer crystals. Lobes are diminished.

109
Q

What is Subdicing?

A

a crystal is divided into a group of smaller crystals called sub-elements. These are electronically joined and act as if they are a single crystal, which reduces grating lobes.

110
Q

Transducers are designed to keep the sound beam narrow over a substantial depth range. How is this accomplished ?

A

Dynamic aperture

111
Q

Dynamic aperture

A

can be used to make a sound beam narrow which improves lateral resolution at a wide range of depths

112
Q

Aperture (variable aperture or dynamic aperature)

A

is a process the ultrasound system does by changing the # of crystals along the face of the probe used to transmit pulses and receive reflections.

CMI 350 (11 decks)

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