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JJ > Diagnostic Imaging - Ultrasound > Flashcards

Diagnostic Imaging - Ultrasound Flashcards

1
Q

what type of waves does diagnostic ultrasound use?

A

high frequency sound waves

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2
Q

what are the frequencies typically used in diagnostic ultrasound?

A

2-18 MHz

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3
Q

what level of Hz is audible sound?

A

20-20,000 Hz

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4
Q

how do sound waves and x rays differ?

A

sound waves need a material to travel through

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5
Q

why are soundwaves unable to move through a vacuum?

A

rely on compression and relaxation of the medium that they are traveling through

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6
Q

what does the velocity of a soundwave depend on?

A

the material it is traveling through - higher density will lead to higher velocity

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7
Q

what effect is relied upon to produce ultrasound?

A

piezoelectric effect

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8
Q

how does the piezoelectric effect work?

A

electrical voltage is applied to a disc within a transducer
the disc expands or contracts due to electrical current
movement is proportional to voltage and gives rise to sound wave

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9
Q

what is the piezoelectric effect?

A

conversion of kinetic energy to sound energy

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10
Q

what are the 2 types of disc used in production of ultrasound?

A

PZT

PVDF

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11
Q

what does PZT stand for?

A

lead ziconate titanate

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12
Q

what does PVDF stand for?

A

polyvinylidine difluoride

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13
Q

describe how ultrasound is produced

A

voltage applied across crystal
crystal deforms due to its piezoelectric properties
leads to emission of high frequency sound waves

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14
Q

is production of ultrasound in the transducer continuous?

A

no - transducer sends out a pulse of sound

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15
Q

how long is the pulse of sound emitted by the the transmitter usually?

A

typically 3 wavelengths - 1.5 mm

3 compressions and relaxations

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16
Q

what happens between pulses of ultrasound?

A

scanner waits for echos from tissues

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17
Q

what percentage of the time it is being used it the transducer producing ultrasound?

A

1% of the time

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18
Q

what percentage of the time it is being used it the transducer receiving ultrasound?

A

99%

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19
Q

how is the ultrasound signal received and an image produced?

A

sound wave returns from tissues to transducer
pressure of sound waves distorts disc and so piezoelectric crystal
generates a voltage proportional to pressure
voltage is then processed by the machine and displayed

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20
Q

describe the piezoelectric effect

A 
voltage 
deforms piezoelectric disc in transducer
pulse of sound into tissue
hits tissue interface
reflection from tissue interface
returning echo of sound
deforms piezoelectric disc in transducer
voltage
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21
Q

define acoustic impedance

A

density of tissue x speed of sound in tissue

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22
Q

what has the most effect on acoustic impedance?

A

density of tissues

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23
Q

how do tissues vary?

A

in acoustic impedance

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24
Q

what happens when a sound crosses a boundary between tissues of different acoustic impedance?

A

some is reflected back to transducer

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25
Q

what does the proportion of reflected sound depend on?

A

difference in acoustic impedance of tissues

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26
Q

how much reflection of ultrasound is seen at soft tissue boundaries?

A

relatively little (e.g. fat / kidney interface)

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27
Q

how much reflection of ultrasound is seen at interface between soft tissue and bone?

A

much larger percentage - bone surface will appear very bright

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28
Q

when does specular (mirror) reflection occur?

A

when ultrasound beam hits a large smooth surface (e.g. small intestine wall)

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29
Q

when does non-specular reflection occur?

A

beam hits small structures which have density variations

the beam is re-radiated in all directions leading to weak echoes

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30
Q

what is enabled by non-specular reflection?

A

texture is given to organs which allows assessment

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31
Q

describe how echoes are detected

A

sound waves reflected from various acoustic interfaces within the body
the echoes deform the crystal, resulting in the production of electrical signals
electrical signals are displayed as image on screen

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32
Q

what are the 3 display modes of ultrasound images?

A

A mode
B mode
M mode

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33
Q

what is B display mode for ultrasound?

A

brightness

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34
Q

what is M display mode for ultrasound?

A

motion

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35
Q

what is A display mode for ultrasound?

A

amplitude - oldest method, only used in opthalmology

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36
Q

how is the image produced in b mode?

A

images a slice thorough a patient with a line of ultrasound
beam of ultrasound scans back and forth
image is produced from lots of lines

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37
Q

what does the brightness of an ultrasound image in B mode depend on?

A

amplitude of signal - stronger echo will be brighter

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38
Q

what does the position of a structure on the screen depend on?

A

time for the signal to return (longer time = further depth)

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39
Q

why must organs be scanned in more than one plane in B mode?

A

as it only images a slice so full impression cannot be gained from one view only

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40
Q

when is M mode most commonly used?

A

cardiac work

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41
Q

how is B mode utilised to aid M mode?

A

B mode image is used to position a single line - movements along this line are followed

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42
Q

how is the image in M mode displayed?

A

position vs. time

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43
Q

how is a trace of movement developed in M mode?

A

continuous updating

44
Q

what is being shown by the yellow line in this B mode ultrasound?

A

the area being imaged in M mode

45
Q

in what state of consciousness can an ultrasound exam be completed?

A

tolerated well fully conscious or with light sedation

deeper sedation may be required for abdominal exam

46
Q

what are the main benefits of ultrasound exam?

A

relatively quick (e.g. diagnosis of pyometra)
non-invasive
safe

47
Q

what considerations should be made when choosing the area of the body to place the transducer?

A

area of the body which overlies the region of interest, avoiding interveneing bone or (where possible) gas

48
Q

how should the area be prepared for ultrasound?

A

clip
clean the skin
apply ultrasound gel

49
Q

when cleaning the skin why may surgical spirit not be the best option?

A

may damage transducer

50
Q

what are the 2 types of arrays found in transducers?

A

phased

linear

51
Q

is on type of transducer going to work for all imaging?

A

no - need a range of frequencies and types for optimal examination

52
Q

what 3 factors can be considered when choosing transducers?

A

type
footprint
frequency

53
Q

what are the 3 types of transducer?

A

phased array
linear array
microconvex / convex

54
Q

how is the beam steered in phased array?

A

electronically

55
Q

what size footprint does a phased array have?

A

small

56
Q

why does phased array produce a triangular shaped image?

A

sound waves diverge the further into tissue they move

57
Q

how does a linear array transducer work?

A

multiple elements are triggered in groups

image is the width of the transducer as waves don’t diverge

58
Q

how are the elements on microconvex / convex transducers arranged?

A

in a curve

59
Q

what is a benefit of microconvex / convex transducers?

A

contour better with the animal

60
Q

does the wave diverge in a microconvex / convex transducer?

A

yes

61
Q

what is the key difference between microconvex and convex transducers?

A

size of footprint - larger in convex

62
Q

what are phased array transducers useful for?

A

cardiac work - sit between ribs but larger image can be produced at depth due to divergence of beam

63
Q

what is a linear array transducer useful for?

A

limbs

64
Q

describe the similarities between phased array and microconvex transducers

A

easy to manipulate
small contact area
wide field at depth

65
Q

describe the linear array transducers

A

large contact area

large field of view near skin

66
Q

why are linear array transducers useful for superficial structures?

A

large field of view near the skin

67
Q

what happens to wavelength as frequency increases?

A

wavelength decreases

68
Q

what is a benefit of shorter wavelengths?

A

better resolution as pulse length is smaller

69
Q

how does shorter pulse length lead to better resolution?

A

better separation between structures as there is no overlap of reflections that can be seen with longer wavelengths

70
Q

what frequencies of ultrasound give good image resolution?

A

7.5-18 mHz

71
Q

what is the cost of using high frequency ultrasound?

A

sound attenuation is proportional to frequency so sound will not penetrate as far into the body

72
Q

what can high frequency ultrasound be used to image?

A

superficial structures in larger animals (e.g. eyes, tendons)

73
Q

what can low frequency ultrasound be used to image?

A 
deeper structures (e.g. the liver in large dogs)
large animals (e.g. horses)
74
Q

what is the resolution like of lower frequency ultrasound transducers?

A

poor

75
Q

what cna be imaged with lower frequency ultrasound transducers?

A

deeper structures

76
Q

what range are lower frequency transducers?

A

2.5 - 5 MHz

77
Q

when should patients be starved overnight for ultrasound?

A

abdominal ultrasound

78
Q

why should patients be starved for abdominal ultrasound?

A

empty stomach is prefurrable
improves ability to examine organs
can safely sedate or GA if needed

79
Q

what is essential when performing ultrasound?

A

good contact with skin

still patient

80
Q

how can good contact with the skin during ultrasound be achieved?

A

clipping
surgical spirit
coupling gel

81
Q

what are the issues with using surgical spirit alongside coupling gel?

A

can damage transducer

82
Q

describe clipping required for an abdominal ultrasound

A

xiphisternum to pubis
line of costal arch up to lumbar muscles
include last 2-3 intercostal spaces

83
Q

describe the clipping site for heart ultrasound

A

right side
(and left for full echo)
4th to 6th intercostal space
costochondral junction to sternum

84
Q

where can the 4th to 6th intercostal space be located?

A

just behind elbow

85
Q

describe clipping sites for left kidney

A

behind last rib

below lumbar muscles

86
Q

describe clipping site for right kidney

A

include last 2-3 intercostal spaces

below lumbar muscle

87
Q

what is involved in ultrasound machine care?

A

regular cleaning of transducers and key board
removal of gel and hair after each use
safe storage of transducers and leads
regular servicing of machine

88
Q

what should be kept on record regarding ultrasound?

A

patients and areas imaged

89
Q

how may a permanent record of ultrasound findings be kept?

A

digital archive
thermal printer
video

90
Q

what does the appearance of tissues on ultrasound relate to?

A

echogenicity

91
Q

how does fluid appear on ultrasound?

A

black - anechnoic

92
Q

what does anechoic mean?

A

no echoes produced

93
Q

how does fat appear on ultrasound?

A

white - echgenic

94
Q

how to soft tissues appear on ultrasound?

A

variable - hyper/hypoechoic relative to surrounding structures

95
Q

how does a soft tissue / gas interface appear on ultrasound?

A

total reflection of sound

cannot see beyond gas

96
Q

is it possible to ultrasound through bone?

A

no - sound is reflected or absorbed

97
Q

what part of bone can be examined through ultrasound?

A

surface

98
Q

what are the advantages of ultrasound?

A 
widely available
safe for operator and patient
relatively quick
non-invasive (except biopsy)
rarely need GA
sedation is optional but can be helpful
99
Q

what clinical information can be gained from ultrasound?

A

good soft tissue detail
functional information / movement
can guide aspirates / biopsies

100
Q

what is routine ultrasound used for?

A

pregnancy diagnosis and monitoring

101
Q

what is difficult to predict with pregnancy monitoring ultrasound?

A

number of foetuses

102
Q

when can ultrasound reliably detect pregnancy in dogs?

A

28 days

103
Q

when can ultrasound reliably detect pregnancy in cats?

A

20 days

104
Q

what are the disadvantages of ultrasound?

A

equipment relatively expensive and easily damaged
need to clip hair (issue in show animals)
need experience ot interpret images

105
Q

what are the issues with clinical information gained from ultrasound?

A

gas/fat/bone hinders exam

many findings are non-specific so biopsy is needed for diagnosis

106
Q

what may hinder ultrasound of the heart?

A

panting so lots of air in lungs

JJ (33 decks)

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