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CVSOH BVSc3 > Diagnostic imaging > Flashcards

Diagnostic imaging Flashcards

1
Q

How are xrays produced?

A

Interaction with fast moving electrons with a metal target

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2
Q

What makes up the cathode?

A

Tungsten wire filament

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3
Q

How are free electrons produced at the cathode?

A

Electrical current is run through the tungsten wire filament causing a cloud of free electrons which are focussed into a beam by a negatively charged focussing cup

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4
Q

What is the relationship between current and no of electrons?

A

More current = higher no of electrons

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5
Q

What is the anode made of?

A

Solid tungsten

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6
Q

What are the two mechanisms of xray formation?

A

General emission - ‘braking’ speed

Characteristic emission - electron knocked out of atom

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7
Q

What is the area of the anode that is hit by electrons and produces xrays called?

A

Focal spot

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8
Q

What is produced when electrons interact with the anode?

A

Heat and x-rays

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9
Q

How does a stationary anode remove heat?

A

Conduction - copper

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10
Q

How does a rotating anode remove heat?

A

Convection - molybdenum

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11
Q

How does a high voltage (kV) affect xrays?

A

Electrons travel faster, have more kinetic energy so xrays have a higher ENERGY

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12
Q

When do you use higher voltage (kV)?

A

When radiographing thicker parts of the body - more penetration

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13
Q

What affect the quantity of xrays produced?

A

mA and time

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14
Q

What is the inverse square law?

A

The exposure is inversely proportional to the square of the distance from the xray tube

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15
Q

What is used to filter out low energy xrays?

A

Thin sheet of aluminium

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16
Q

What are the three ways xrays interact with matter?

A

Pass through unchanged
Absorbed
Scattered

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17
Q

What factors affect absorption of xrays?

A

Atomic number
Density
Thickness

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18
Q

What does xray image formation depend on?

A

Differential absorption

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19
Q

What does computed radiography use to capture the image?

A

A storage phosphor plate

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20
Q

How is the storage phosphor plate read?

A

Energy is stored in plate and later excited by a laser beam in a plate reader and converted to electrical signal

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21
Q

What does direct digital radiography use to capture the image?

A

Electronic detector

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22
Q

What is contrast?

A

The difference in density between two adjacent areas on a radiograph

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23
Q

How does voltage affect contrast?

A

Higher kV increases penetration so lowers the contrast

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24
Q

How does scattered radiation affect contast?

A

Causes overall blackening of the film so reduces contast

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25
Q

How do you reduce scattering of radiation?

A

Use a grid

Collimation

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26
Q

What is collimation?

A

Reducing the size of the primary beam to the area of anatomy that we want to see

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27
Q

When are grids used?

A

When radiographing thicker objects

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28
Q

What are grids made up of?

A

Thin lead strips alternating with thin radiolucent strips

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29
Q

What is a side effect of using a grid?

A

Need to increase the exposure

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30
Q

What is the grid factor?

A

Multiple of mAs needed when using grid compared to same exposure without grid

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31
Q

What does the grid factor tend to be?

A

2-6x

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32
Q

What are the different grid types?

A

Parallel

Focussed

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33
Q

What is a side effect of using a parallel grid?

A

Get cut off on the sides

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34
Q

What do you have to make sure when using a focussed grid?

A

Its the right way up otherwise will get massive cut off

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35
Q

How do you alter the collimation?

A

Using a light beam diaphragm to alter aperture size

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36
Q

What affects the sharpness of radiographs?

A

Movement blur
Focal spot size
Distance

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37
Q

What is the focal spot?

A

Point of xray source

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38
Q

How does focal spot affect the sharpness of the image?

A

Smaller focal spot = sharper image

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39
Q

What are the two distances that affect sharpness?

A

Film/focal spot distance

Object/film distance

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40
Q

What is the focal film distance?

A

The distance from the x-ray tube to the film plate

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41
Q

How does focal film distance affect sharpness?

A

The closer the x ray machine is, the more divergence there is so its less sharp

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42
Q

What does penumbra mean?

A

Spread of xrays after a point when they start to diverge

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43
Q

What is the object film distance?

A

Distance between the object (animal) and the film plate

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44
Q

How does the object film distance affect the sharpness?

A

Larger OFD leads to larger penumbra and so less sharpness - want to be as close as possible

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45
Q

How is magnification calculated using the two distances?

A

FFD/(FFD-OFD)

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46
Q

How do you reduce magnification?

A

Longer FFD

Shorter OFD

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47
Q

When does distortion occur?

A

When an object is not parallel to the film

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48
Q

What is a film fault only found on cassette based systems?

A

Double exposure - two images on one plate

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49
Q

What is a sign of underexposure in digital photography?

A

Very grainy and pixelated image

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50
Q

How do you correct underexposure?

A

Increase exposure factors - kV and/or mA

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51
Q

What causes the Uberschwinger artefact in radiographs?

A

When there is a large density difference between adjacent objects

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52
Q

What does the Uberschwinger artefact look like in radiographs?

A

Excessive edge enhancement causing radiolucent black ring around artefact

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53
Q

What causes a ghost artefact in radiographs?

A

Incomplete erasure of a plate

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54
Q

What are moire artefacts in radiographs?

A

Bands across image

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55
Q

What causes moire artefacts in radiographs?

A

Interference between the frequency of the laser reader and the grid

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56
Q

What can cause one line across the radiograph image?

A

Dirt in the cassette reader eg. dust particle

57
Q

What is the ALARA principle?

A

As Low As Reasonaby Achievable - radiation

58
Q

What methods of protection are used for radiation?

A

Space/distance
Barriers
Protective clothing
Time

59
Q

What legislation surrounds radiation?

A

Ionising radiation regulations 2017

60
Q

What personnel are required for radiation legislation?

A

Radiation protection advisor - external

Radiation protection supervisor - internal

61
Q

How big should the controlled area for radiation use be?

A

2m - when it is connected to the mains supply

62
Q

What is the device called that monitor radiation levels on individuals?

A

Dosimeters

63
Q

What is the legal dose limit for workers over 18?

A

6mSv

64
Q

What is an MRI?

A

Cross sectional imaging technique - slices

65
Q

What does MRI use to generate images?

A

Radiowaves and a strong magnet - pulses and echoes

66
Q

What are some advantages of MRI?

A

Good for soft tissue
Doesnt use ionising radiation
Good for imaging areas which arent very accessible eg. brain and spinal cord

67
Q

What are some disadvantages of MRI?

A

Expensive
Need to be perfectly still
No metal

68
Q

What is an artefact in MRIs?

A

Metal distorts magnetic field eg. microchip

69
Q

What does CT stand for?

A

Computed tomography

70
Q

How does CT generate and image?

A

Ionising radiation - ring of rotating xray detectors

71
Q

How is the CT information displayed?

A

Different planes and windows

72
Q

What is CT used for?

A

Anatomical reconstructions of bony structures eg. complex joints
Also lymph nodes, lungs

73
Q

How is CT better than radiographs?

A

Avoids superimposition of structures - can get 3D structures

74
Q

What are some disadvantages of CT?

A

Not widely available

Ionising radiation - higher dose than radiography

75
Q

What does scintigraphy use to generate an image?

A

Radioisotope - technetium 99m gives out gamma rays

Bound to a substance that binds to a specific area of the body eg. bone

76
Q

How does scintigraphy work?

A

Bound isotope is injected IV

Pattern of radiation emitted is analysed

77
Q

What are the main uses of scintigraphy?

A

Skeletal injury in horses

Ectopic thyroid tissue in hyperthyroid cats

78
Q

What are some advantage of scintigraphy?

A

Can localise problems that cant be seen otherwise

Assesses function, not just structure as depends on metabolism

79
Q

What are some disadvantages of scintigraphy?

A

Uses ionising radiation
Remains radioactive for a while
Poor anatomical detail

80
Q

What does an ultrasound use to generate an image?

A

High frequency sound waves - 2-18 MHz

81
Q

How are ultrasound waves produced?

A

Disc in a transducer has voltage applied and expands and contracts proportional to the voltage
This movement causes sound waves

82
Q

What is the piezoelectric effect?

A

Conversion of electrical energy to kinetic energy and therefore a sound wave

83
Q

How are ultrasounds read?

A

Sound returns to the transducer
Pressure of the sound wave distorts the disc generating voltage proportional to the pressure
Voltage processed by machine

84
Q

What is acoustic impedance?

A

Density of tissue x speed of sound in tissue

85
Q

What does a change in acoustic impedance cause?

A

Reflection of ultrasound waves

86
Q

What is non-specular reflection?

A

When beam hits small structures and is re-radiated in all directions - causes texture to organs

87
Q

What are the two display modes of ultrasound?

A

B mode - brightness

M mode - motion

88
Q

How does the B mode of ultrasound work?

A

Images a slice - image built up of lots of lines of ultrasound beam
See movement in real time

89
Q

What does brightness depend on in B mode of ultrasound?

A

Amplitude of signal

90
Q

What does position depend on in B mode of ultrasound?

A

Time the signal takes to return

91
Q

When is M mode of ultrasound used?

A

In cardiac work

92
Q

How does the M mode of ultrasound work?

A

Movement of points along a single line - position vs time

93
Q

What do you need to avoid when doing an ultrasound exam?

A

Bone or gas

Hair

94
Q

What do you need to use with the ultrasound transducer?

A

Acoustic gel

95
Q

What are the three different types of ultrasound transducers?

A

Phased
Linear
Convex

96
Q

What is a phased transducer?

A

Beam is steered electronically

Diverges at depth - end up with a fan shaped image

97
Q

What is a linear transducer?

A

Beam is steered manually

Multiple elements - triggered in groups

98
Q

What is a convex transducer?

A

Elements are arranged in a curve

99
Q

Which transducer is better for superficial structures?

A

Linear

100
Q

What are the advantages of a phased array?

A

Easy to manipulate
Small contact area
Wide field at depth

101
Q

What does a high frequency of ultrasound give?

A

Good image resolution

But cant penetrate as far

102
Q

What are high frequency ultrasounds used for?

A

Superficial structures in larger animals

All structures in smaller animals

103
Q

What do low frequency ultrasounds give?

A

Poorer resolution

Can image deeper structures

104
Q

What are low frequency ultrasounds used for?

A

Deeper structures

Larger animals

105
Q

What does hyperechoic mean?

A

Appears white on ultrasound image

106
Q

What does hypoechoic mean?

A

Appears grey on ultrasound image

Often used as a relative term

107
Q

What does anechoic mean?

A

Appears black on ultrasound image

108
Q

What does echogenic mean?

A

Appears white on ultrasound image - same as hyperechoic

109
Q

What does echolucent mean?

A

Appears black on ultrasound image - same as enechoic

110
Q

What are 4 common ultrasound artefacts?

A

Acoustic enhancement
Acoustic shadowing
Reverberation
Mirror image

111
Q

What is acoustic enhancement?

A

Brighter area distal to fluid filled structures

112
Q

Why does acoustic enhancement occur?

A

Low attenuating structure so no echoes are caused

Then structures deeper to it cause echoes that it thinks are denser so is brighter

113
Q

What is acoustic shadowing?

A

A black area below a structure that is highly attenuating/causes lots of reflection

114
Q

What transition causes the most acoustic shadowing?

A

Soft tissue to gas

Soft tissue to bone is slightly less

115
Q

What causes reverberation artefacts on ultrasound scan?

A

When sound bounces between interfaces giving multiple echoes
Mainly gas interfaces - closely spaced reflective surfaces

116
Q

What do reverberation artefacts look like?

A

Comet tail

117
Q

When do mirror image artefacts occur?

A

At highly reflective interfaces - typically diaphragm-lung interface

118
Q

What does a mirror image artefact look like?

A

Bright white line with mirror image of the liver on either side

119
Q

What are the advantages of ultrasound?

A

Quick
Safe
Non-invasive
Real time

120
Q

What are the disadvantages of ultrasound

A

Need to clip hair
Gas and fat hinder
Needs experience
Non-specific findings eg. dont know what the lesion is

121
Q

What is the doppler shift in ultrasound?

A

When the sound waves hit small moving targets eg. RBC

Changes the frequency of the sound

122
Q

What can you use doppler ultrasound for?

A

Direction of blood flow
Velocity of blood flow
Turbulent blood flow

123
Q

What are the Roentgen signs for in radiology?

A

Features that help you to filly describe a lesion

124
Q

What are the 6 Roentgen signs in radiology?

A 
Size
Shape
Position
Opacity
Margination
Number
125
Q

How is size used as a Roentgen sign?

A

Measured relative to other organs - increase or decrease

May become apparent or displace another organ

126
Q

How can you tell if shape and position of a structure has changed in a radiograph?

A

Know what normal is

127
Q

What can cause an increase in opacity on a radiograph?

A

Excess fluid or soft tissue
Deposition of bone/calcium
Foreign body

128
Q

What can cause a decrease in opacity on a radiograph?

A

Abnormal gas accumulation

Loss of normal tissue eg. demineralisation

129
Q

What can cause poorly defined marginations on a radiograph?

A

Abdominal fluid
Inflammatory change
Malignant bone lesions

130
Q

What is different in the Roentgen signs between radiologic and ultrasonographic?

A

Echogenicity in ultrasounds rather than opacity

131
Q

What can make structures more hyperechoic/brighter on ultrasound?

A

Fat
Glycogen
Collagen
Crystalline material

132
Q

What can make structures more hypoechoic/darker on ultrasound?

A

Oedema

133
Q

Out of the spleen, kidney and liver, which is the most echogenic and which is the least ecogenic?

A

Spleen is most echogenic/bright
Then liver
Then kidney is the least echogenic

134
Q

How does the gall bladder present on ultrasound?

A

Anechoic

135
Q

What does the stomach look like on an ultrasound?

A

5 layered appearance

Has rugal folds

136
Q

How does the renal medulla present on ultrasound compared to the cortex?

A

Hypoechoic to anechoic - much blacker

137
Q

What does the bladder look like on ultrasound?

A

Echogenic double line with thin muscle layer between - hypoechoic

138
Q

What are radiographs better at imaging than ultrasound?

A

Fat, air

139
Q

What are radiographs worse at imaging than ultrasounds?

A

Fluid, soft tissue

CVSOH BVSc3 (60 decks)

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