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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
what does the proportion of reflected sound depend on?
difference in acoustic impedance of tissues
26
how much reflection of ultrasound is seen at soft tissue boundaries?
relatively little (e.g. fat / kidney interface)
27
how much reflection of ultrasound is seen at interface between soft tissue and bone?
much larger percentage - bone surface will appear very bright
28
when does specular (mirror) reflection occur?
when ultrasound beam hits a large smooth surface (e.g. small intestine wall)
29
when does non-specular reflection occur?
beam hits small structures which have density variations | the beam is re-radiated in all directions leading to weak echoes
30
what is enabled by non-specular reflection?
texture is given to organs which allows assessment
31
describe how echoes are detected
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
32
what are the 3 display modes of ultrasound images?
A mode B mode M mode
33
what is B display mode for ultrasound?
brightness
34
what is M display mode for ultrasound?
motion
35
what is A display mode for ultrasound?
amplitude - oldest method, only used in opthalmology
36
how is the image produced in b mode?
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
37
what does the brightness of an ultrasound image in B mode depend on?
amplitude of signal - stronger echo will be brighter
38
what does the position of a structure on the screen depend on?
time for the signal to return (longer time = further depth)
39
why must organs be scanned in more than one plane in B mode?
as it only images a slice so full impression cannot be gained from one view only
40
when is M mode most commonly used?
cardiac work
41
how is B mode utilised to aid M mode?
B mode image is used to position a single line - movements along this line are followed
42
how is the image in M mode displayed?
position vs. time
43
how is a trace of movement developed in M mode?
continuous updating
44
what is being shown by the yellow line in this B mode ultrasound?
the area being imaged in M mode
45
in what state of consciousness can an ultrasound exam be completed?
tolerated well fully conscious or with light sedation | deeper sedation may be required for abdominal exam
46
what are the main benefits of ultrasound exam?
relatively quick (e.g. diagnosis of pyometra) non-invasive safe
47
what considerations should be made when choosing the area of the body to place the transducer?
area of the body which overlies the region of interest, avoiding interveneing bone or (where possible) gas
48
how should the area be prepared for ultrasound?
clip clean the skin apply ultrasound gel
49
when cleaning the skin why may surgical spirit not be the best option?
may damage transducer
50
what are the 2 types of arrays found in transducers?
phased | linear
51
is on type of transducer going to work for all imaging?
no - need a range of frequencies and types for optimal examination
52
what 3 factors can be considered when choosing transducers?
type footprint frequency
53
what are the 3 types of transducer?
phased array linear array microconvex / convex
54
how is the beam steered in phased array?
electronically
55
what size footprint does a phased array have?
small
56
why does phased array produce a triangular shaped image?
sound waves diverge the further into tissue they move
57
how does a linear array transducer work?
multiple elements are triggered in groups | image is the width of the transducer as waves don't diverge
58
how are the elements on microconvex / convex transducers arranged?
in a curve
59
what is a benefit of microconvex / convex transducers?
contour better with the animal
60
does the wave diverge in a microconvex / convex transducer?
yes
61
what is the key difference between microconvex and convex transducers?
size of footprint - larger in convex
62
what are phased array transducers useful for?
cardiac work - sit between ribs but larger image can be produced at depth due to divergence of beam
63
what is a linear array transducer useful for?
limbs
64
describe the similarities between phased array and microconvex transducers
easy to manipulate small contact area wide field at depth
65
describe the linear array transducers
large contact area | large field of view near skin
66
why are linear array transducers useful for superficial structures?
large field of view near the skin
67
what happens to wavelength as frequency increases?
wavelength decreases
68
what is a benefit of shorter wavelengths?
better resolution as pulse length is smaller
69
how does shorter pulse length lead to better resolution?
better separation between structures as there is no overlap of reflections that can be seen with longer wavelengths
70
what frequencies of ultrasound give good image resolution?
7.5-18 mHz
71
what is the cost of using high frequency ultrasound?
sound attenuation is proportional to frequency so sound will not penetrate as far into the body
72
what can high frequency ultrasound be used to image?
superficial structures in larger animals (e.g. eyes, tendons)
73
what can low frequency ultrasound be used to image?
``` deeper structures (e.g. the liver in large dogs) large animals (e.g. horses) ```
74
what is the resolution like of lower frequency ultrasound transducers?
poor
75
what cna be imaged with lower frequency ultrasound transducers?
deeper structures
76
what range are lower frequency transducers?
2.5 - 5 MHz
77
when should patients be starved overnight for ultrasound?
abdominal ultrasound
78
why should patients be starved for abdominal ultrasound?
empty stomach is prefurrable improves ability to examine organs can safely sedate or GA if needed
79
what is essential when performing ultrasound?
good contact with skin | still patient
80
how can good contact with the skin during ultrasound be achieved?
clipping surgical spirit coupling gel
81
what are the issues with using surgical spirit alongside coupling gel?
can damage transducer
82
describe clipping required for an abdominal ultrasound
xiphisternum to pubis line of costal arch up to lumbar muscles include last 2-3 intercostal spaces
83
describe the clipping site for heart ultrasound
right side (and left for full echo) 4th to 6th intercostal space costochondral junction to sternum
84
where can the 4th to 6th intercostal space be located?
just behind elbow
85
describe clipping sites for left kidney
behind last rib | below lumbar muscles
86
describe clipping site for right kidney
include last 2-3 intercostal spaces | below lumbar muscle
87
what is involved in ultrasound machine care?
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
what should be kept on record regarding ultrasound?
patients and areas imaged
89
how may a permanent record of ultrasound findings be kept?
digital archive thermal printer video
90
what does the appearance of tissues on ultrasound relate to?
echogenicity
91
how does fluid appear on ultrasound?
black - anechnoic
92
what does anechoic mean?
no echoes produced
93
how does fat appear on ultrasound?
white - echgenic
94
how to soft tissues appear on ultrasound?
variable - hyper/hypoechoic relative to surrounding structures
95
how does a soft tissue / gas interface appear on ultrasound?
total reflection of sound | cannot see beyond gas
96
is it possible to ultrasound through bone?
no - sound is reflected or absorbed
97
what part of bone can be examined through ultrasound?
surface
98
what are the advantages of ultrasound?
``` widely available safe for operator and patient relatively quick non-invasive (except biopsy) rarely need GA sedation is optional but can be helpful ```
99
what clinical information can be gained from ultrasound?
good soft tissue detail functional information / movement can guide aspirates / biopsies
100
what is routine ultrasound used for?
pregnancy diagnosis and monitoring
101
what is difficult to predict with pregnancy monitoring ultrasound?
number of foetuses
102
when can ultrasound reliably detect pregnancy in dogs?
28 days
103
when can ultrasound reliably detect pregnancy in cats?
20 days
104
what are the disadvantages of ultrasound?
equipment relatively expensive and easily damaged need to clip hair (issue in show animals) need experience ot interpret images
105
what are the issues with clinical information gained from ultrasound?
gas/fat/bone hinders exam | many findings are non-specific so biopsy is needed for diagnosis
106
what may hinder ultrasound of the heart?
panting so lots of air in lungs

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