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Registry Review Class > SPI 2 > Flashcards

SPI 2 Flashcards

1
Q

Beam width

A

As sound travels the width of the beam changes.
Start- same size as transducer diameter (aperture)

Gets progressively narrower until it reaches smallest diameter

Then diverges

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2
Q

Focus (focal point)

A

Location where beam reaches its minimum diameter.

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3
Q

Focal depth (focal length, near zone length)

A

The DISTANCE from the transducer face to the focus.

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4
Q

Near zone (Fresnel zone)

A

The REGION or zone in between the transducer and the focus

Sound beams converge here

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5
Q

Far zone (Fraunhofer zone)

A

The REGION or zone deeper than the focus, beyond the near field.

Sound beam diverges here.

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6
Q

Focal zone

A

Region surrounding the focus where the beam is “sort of narrow”

Picture is relatively good here.

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7
Q

Beam Diameter at transducer

A

Same as transducer diameter

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8
Q

Beam Diameter at end of near zone

A

1/2 of transducer diameter

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9
Q

Beam Diameter at 2 near zone lengths

A

Same as transducer diameter

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10
Q

Beam Diameter deeper than 2 near zone lengths

A

Greater than transducer diameter

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11
Q

Focal depth is determined by

A 
Transducer diameter (aperture)
Frequency
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12
Q

Shallow focus (focal depth)

A

Small diameter, low frequency

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13
Q

Deep focus (focal depth)

A

Large diameter, high frequency

Have lower intensity at focus than shallow

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14
Q

Sound beam divergence

A

Describes the spread of the sound beam in the deep far zone

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15
Q

Sound beam divergence is determined by

A

Transducer diameter

Frequency of the ultrasound

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16
Q

Less divergence

A

Narrower beam in far field, large diameter crystal, high frequency, improved lateral resolution in field

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17
Q

More divergence

A

Wider beam in far field, smaller diameter crystal, low frequency, degraded lateral resolution in far field.

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18
Q

Diffraction

A

V-shaped wave (Huygen’s wavelet)
Produced by tiny source with a size near the wavelength of the sound.
Waves diverge in this shape as they propogate.

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19
Q

Huygen’s principle

A

Hourglass shape of sound beam.

Result of the constructive and destructive interference of many sound wavelets emitted from numerous sound sources.

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20
Q

Resolution

A

The ability to image accurately

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21
Q

Axial resolution

A

Ability to distinguish two structures that are close to each other front to back, parallel to, or along the beam’s main axis

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22
Q

LARRD

A 
Longitudinal
Axial
Range
Radial
Depth
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23
Q

Axial resolution is measured in what units?

A

Units of distance (mm, cm)

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24
Q

Shorter pulses provide what?

A

Better axial resolution

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25
Q

Can sonographer change axial resolution ?

A

No

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26
Q

“Short pulse” means?

A

Short spatial pulse length or a short pulse duration

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27
Q

Equation for axial res.

A

Axial res. (mm)= SPL (mm)/2

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28
Q

Axial res. Inproves with

A

Less ringing

Higher frequency

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29
Q

Axial res. is best using

A

Highest frequency and fewest number of cycles per pulse

Think of this with numerical questions

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30
Q

Lateral resolution

A

Minimum distance that two structures are separated by side to side, or perpendicular to the sound beam that produces two distant echoes

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31
Q

LATA

A

Lateral
Angular
Transverse
Azimuthal

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32
Q

Units of lateral res.

A

All units of length (mm)

A smaller number creates more accurate image

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33
Q

Lateral res. is equal to

A

Beam diameter

Beam width variation

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34
Q

Lateral res is best at

A

The focus because it is the narrowest

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35
Q

Lateral res. is not as good as

A

Axial resolution

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36
Q

Axial and lateral res. In high frequency pulsed US

A

Improved axial res. entire image

Inproved lateral res. In the far, far field (at depths greater than twice the focal depth)

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37
Q

Focusing alters the beam in what three ways?

A

Narrower “waist” in the US beam
shallower focus
smaller focal zone

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38
Q

Focusing is effective mainly where?

A

the near field and the focal zone

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39
Q

types of focus

A

fixed focus

adjustable

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40
Q

fixed focus

A

conventional or mechanical
-Lens external focus
-curved PZT crystal- internal focusing
poorest lateral resolution since not adjustable

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41
Q

adjustable focus

A

phased array-by electronics better lateral res.
electric focusing- adjustable
multi-focusing

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42
Q

single crystal transducers are what type of focus?

A

always fixed focus

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43
Q

2-D imaging is also called

A

B-scan or B-mode

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44
Q

Mechanical transducer characteristics

A 
Image shape- sector
steering- mechanical
focusing- fixed (conventional)
number of crystals and shape- 1, disc
crystal defect- image loss
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45
Q

Linear switched transducer characteristics

A 
image shape- rectangular
steering- none
focusing- fixed
number and crystal shape- approx. 200, rectangular
crystal defect- vertical line dropout
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46
Q

Linear phased array transducer characteristics

A

Image shape- sector
steering- electronic
focusing- electronic
number and shape of crystals- approx 200, rectangular
crystal defect- poor steering and focusing

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47
Q

Annular phased transducer characteristics

A

image shape- sector
steering- mechanical
focusing- electronic
number and shape of crystals- approx. 5, ring

48
Q

Convex sequential transducer characteristics

A 
image shape- blunted sector
steering- none
focusing- fixed
number and shape of crystals- approx. 200, rectangular
crystal defect- vertical dropout
49
Q

Convex phased transducer characteristics

A

image shape- blunted sector
steering- electronic
focusing- electronic
number and shape of crystals- approx. 200, rectangular
crystal defect- poor steering and focusing

50
Q

Vector transducer characteristics

A

image shape- flat top sector (trapezoid)
steering- electronic
focusing-electronic
number and shape of crystals- approx 200, rectangular
crystal defect- poor steering and focusing

51
Q

contrast resolution

A

visualizing a variety of gray shades in an image

52
Q

poor contrast resolution has

A

few gray shades

53
Q

good contrast resolution has

A

many gray shades

54
Q

spatial resolution

A

visualizing general detail in an image

55
Q

spatial resolution is affected by

A

axial resolution, lateral resolution, gaps between scan lines

56
Q

poor spatial resolution

A

limited detail

57
Q

good spatial resolution

A

fine detail

58
Q

temporal resolution

A

ability to accurately locate moving structures at any particular instant in time

59
Q

temporal resolution is determined by

A

frame rate only

60
Q

frame rate units

A

hertz Hz

61
Q

frame rate is determined by what two factors?

A 
imaging depth
# of pulses per image
62
Q

frame rate is limited by what two factors?

A

speed of sound in medium

imaging depth

63
Q

fundamental limitation of temporal resolution

A

speed.

64
Q

High temporal resolution

A 
high frame rate
shallow imaging
fewer pulses per image
single focusing 
narrow sector
low line density
associated with better movie but lower quality image
65
Q

Low temporal resolution

A

low frame rate
deep imaging
more pulses per image
multi-focusing (improves lateral res)
wide sector
high line density (improves spatial res.)
associated with poor quality movie but higher quality image

66
Q

if imaging depth doubles what happens to the frame rate?

A

it will be halved

67
Q

Master synchronizer

A

communicates with all individual components of US system

organizes and times their functions

68
Q

Transducer

A

converts electrical into acoustic energy during transmission

69
Q

Pulser

A

controls the electrical signals sent to active elements; receives timing signal from synchronizer

70
Q

Pulser determines what?

A

PRP PRF and pulse amplitude

creates firing pattern for phase array systems (beam former)

71
Q

Pulser modes

A 
Continuous wave
Pulsed wave (single crystal)
pulsed wave (arrays)
72
Q

continuous wave

A

constant electrical signal

electrical frequency= sound’s frequency

73
Q

Pulse waves (single crystal)

A

short duration electrical “spike”

one spike per pulse

74
Q

Pulse waves (arrays)

A

many elements fired for each pulse

one electrical “spike” per fire elements

75
Q

Receiver

A

processes electronic signal produced by transducer during reception and produces picture on the screen

76
Q

Display

A

examples include monitor, audio speakers, paper record

77
Q

Storage

A

media is permanently archived to this; ex: computer memory, hard drives

78
Q

Transducer output

A

Determined by excitation voltage from Pulser
PZT crystal vibrates with magnitude related to pulser voltage
when transducer output changes, strength of every pulse transmitted to body changes

79
Q

signal to noise ratio

A

signal- meaningful portion of data

noise- inaccurate portion of data

80
Q

High signal to noise ratio

A

meaningful part of data is stronger than inaccurate portion

81
Q

Low signal to noise ratio

A

inaccurate portion of data is stronger than meaningful part

82
Q

increasing transducer output improves what?

A

signal to noise ratio

83
Q

Receiver functions

A

amplification, compensation, compression demodulation, rejection (hint alphabetical order)

84
Q

Amplification

A

aka receiver gain
adjustable
all signals are treated the same

85
Q

Compensation

A

Time gain compensation TGC, depth compensation DGC
adjustable
signals treated differently based on reflector depth
creates uniform brightness from top to bottom of image
higher frequency more TGC
lower frequency less TGC

86
Q

Compression

A

adjustable, decreases dynamic range, changes gray scale map
allows us to see all gray shades
dB add or subtract

87
Q

Demodulation

A

not adjustable, changes form of signals

88
Q

Reject

A

aka suppression or threshold
adjustable
only weak signals manipulated, strong signals not affected.

89
Q

TGC curve

A 
near gain
delay
slope
knee 
far gain
90
Q

Contrast agents

A

“micro-bubbles”

Injected into the circulation (IV) these agents create strong reflections that actually “light up” blood chambers or vessels.

91
Q

Requirements for contrast agents

A

safe
strong reflector of US
long persistence
metabolically inert

92
Q

adjustments to output power or receiver gain alter what?

A

brightness of the entire image

93
Q

Output Power

A

affects brightness by adjusting strength of sound waves sent to the body from the transducer

affects patient exposure

94
Q

When an image is too bright due to high output power what happens?

A

lateral and longitudinal resolutions degrade

95
Q

Receiver gain

A

affects brightness by changing amplification of electronic signals after returning to the receiver

does not affect patient exposure

96
Q

ALARA (As Low As Reasonably Achievable)

A

when an image is too bright or too dark, changes in output power and receiver gain can enhance the image. As first option always choose the option that will minimize patient exposure.

(decrease output power to decrease patient exposure if image is too bright)

look at pg. 101-104

97
Q

Harmonics (harmonic frequency) imaging creates US scans from sound reflections at

A

twice the transmitted frequency

98
Q

Harmonics are created where?

A

In the tissues (not the transducer or receiver)

99
Q

Fundamental frequency is equal to?

A

the transducer frequency

100
Q

What is non-linear behavior?

A

the small difference between speeds of high and low pressure (compressions and rarefactions of sound)

101
Q

What does non-linear behavior do?

A

distorts the sound waves and creates harmonics

(think uneven) look at pages 105 and 106

102
Q

Bistable properties

A 
black or white
on or off
high contrast
narrow dynamic range
poor contrast resolution
103
Q

Gray scale properties

A 
many shades of gray
multiple levels
low contrast
wide dynamic range
good contrast resolution
104
Q

Brightness

A

related to the brilliance of the image

how “lit up” is the image?

105
Q

Contrast

A

determines the range of brilliancies that are displayed.
(are the whites white? are the blacks black?)
bistable images are high contrast

106
Q

Analog VS. Digital

A

Analog- real world

Digital- computer world

107
Q

Scan converters do what?

A

change the data format from penetrations (spokes) to horizontal lines of a display. Can be manipulated between the storing and displaying of the data
(ex. black on white can be changed to white on black)

108
Q

Computer memory is called?

A

RAM

Random Access Memory

109
Q

What is a Digital Scan Converter?

A

A microprocessor digitizes images. Converts image into numbers which are stored in memory
numbers can be processed and re-translated for display

110
Q

What is a pixel?

A

the smallest element of a digital picture

111
Q

What is pixel density?

A

more pixels per inch, the more detail in the image (spatial or detail resolution)

112
Q

What is a bit?

A

smallest amount of digital storage

113
Q

Bistable

A

having a value of either zero or one

group of bits is assigned to each pixel to store the gray scale color assigned to that pixel

114
Q

The more bits you have per pixel-

A

the more shades of gray and the better the contrast resolution

115
Q

To calculate the # of shades of gray -

A

multiply the number 2 by itself the same # of bits (2^n)

Registry Review Class (6 decks)

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