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Flashcards in Diagnostic Imaging - X-Ray Deck (426)
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1
Q

what does the electromagnetic spectrum consist of?

A

a number of different types of waves including radiowaves, visible light and X-rays

2
Q

do all waves on the electromagnetic spectrum travel at the same speed?

A

yes- speed of light

3
Q

in what direction do all waves from the electromagnetic spectrum travel?

A

in a straight line

4
Q

what is energy inversely proportional to?

A

wavelength

5
Q

describe the energy and wavelength of X-rays

A

high energy

shorter wavelength

6
Q

what is the wavelength?

A

the distance between two consecutive peaks or troughs of a wave

7
Q

what is the frequency of the electromagnetic spectrum?

A

number of times a peak passes a fixed point per second

8
Q

what is the frequency of a wave an indicator of?

A

the energy of a wave

9
Q

how are frequency and wavelength related?

A

inverse relationship - as one increases the other will decrease

10
Q

describe the wavelength and frequency of X rays

A

short wavelength and high frequency

11
Q

how much energy do x rays have?

A

high - due to high frequency

12
Q

what is in the nucleus of an atom?

A

positively charged protons and neutral neutrons

13
Q

what surrounds the nucleus of an atom?

A

electrons (negatively charged)

14
Q

what makes an atom electronically neutral?

A

number of protons = number of electrons

15
Q

what is the atomic number of an element?

A

the number of protons (Z)

16
Q

what is the atomic weight of an element?

A

number of protons plus number of neutrons

17
Q

what does a high atomic number mean in terms of x ray production?

A

high x ray production

18
Q

how are x-rays produced?

A

interaction of fast moving electrons with a metal traget

19
Q

when are x rays used?

A

radiography

20
Q

when are gamma rays produced?

A

decay of radioactive elements

21
Q

when are gamma rays used?

A

nuclear medicine (scintigriphy)

22
Q

what are the 2 main components of the x ray tube?

A

cathode assembly

anode assembly

23
Q

what charge does the anode have?

A

positive

24
Q

what charge does the cathode have?

A

negative

25
Q

what is the cathode?

A

a wire filament made of tungsten

26
Q

what happens when a small electrical current is passed through the cathode filament?

A

it heats up

27
Q

what is caused by the cathode filament heating up?

A

a cloud of free electrons form around the wire

28
Q

what is thermionic emission?

A

heating and the associated release of electrons

29
Q

what is used to keep the cloud of electrons together near the cathode?

A

focussing cup

30
Q

why is the focusing cup near the cathode necessary?

A

electrons would naturally be repelled by the cathode

31
Q

what is found on the anode?

A

tungsten target

32
Q

why is tungsten used?

A

it has a high atomic number and so is efficient at producing x rays

33
Q

why is it necessary for tungsten to have a high melting point?

A

most of the energy produced is heat

34
Q

what happens when potential difference is applied across the tube?

A

electrons hit the target of the anode at speed and produce x-rays

35
Q

how is a potential difference applied across the x-ray tube?

A

the circuit is closed

36
Q

what are the 2 mechanisms of x ray formation?

A

general emission

charactoristic emission

37
Q

how are x rays formed during general emission?

A

rapid deceleration of electrons as they meet tungsten atoms causes energy to be released as x rays

38
Q

how are x rays produced during characteristic emission?

A

incoming electron knocks an electron from the tungsten atoms shell, electrons change shells in order to fill the gap that is left and x rays are produced as a byproduct

39
Q

which is the main mechanism of x ray formation?

A

general emission

40
Q

what is the energy produced by characteristic emission specific to?

A

the atom in use (e.g. tungsten has level of energy that will be produced0

41
Q

is the production of x rays efficient?

A

no - majority of energy produced is heat (99%)

42
Q

what is the focal spot?

A

small area of the anode where electrons from the cathode are focussed

43
Q

what is the key issue when x -rays are being produced?

A

ensuring that heat is dissapated

44
Q

what are the 2 types of anode?

A

stationary

rotating

45
Q

where is the tungsten target located in the stationary anode?

A

in a block of copper

46
Q

what is the benefit of embedding the tungsten target in copper in a stationary anode?

A

alows conduction of heat away from target

47
Q

describe a rotating anode

A

anode is a disc with an angled edge - tungsten track runs around the angled edge

48
Q

what is the disc of the rotating anode mounted on?

A

molybdenum rod

49
Q

what is the disc of a rotating anode rotated by?

A

electric motors

50
Q

what is the purpose of the molybdenum rod found in rotating anodes?

A

poor heat coordinator

51
Q

how is heat lost from the rotating anode?

A

radiation and convection from the surface of the disc

52
Q

how is heat produced around circumference of the disc rather than a single point?

A

cathode is offset and targets the edge of the disc

53
Q

what are the anode and cathode placed in?

A

evacuated (vacuum) pyrex tube

54
Q

why do the anode and cathode need to be within a vacuum?

A

prevents interference of gas with the electrons

55
Q

what is the pyrex tube containing the anode and cathode immersed in?

A

oil - to aid heat conduction and electrical insulation

56
Q

what is the x ray tube surrounded by?

A

lead, to prevent x rays from escaping, apart from a small window through which the useful x ray beam emerges

57
Q

what are the 3 main specifications used during x ray?

A

exposure factors
focal spot
filtration

58
Q

what does the focal spot contribute to?

A

quality of image

59
Q

how are exposure factors altered?

A

via the control panel of the x ray machine

60
Q

what are the settings that contribute to exposure factors?

A

on/off button
kV control
mA cntrol
timer

61
Q

what happens when an x ray machine is connected to a power supply?

A

the area around it is considered in law as a ‘controlled area’ with associated access restrictions

62
Q

why is it important to know the location of the mains power switch?

A

disconnecting the machine from the mains in an emergency will stop the emission of radiation

63
Q

what does kV stand for?

A

kilovalots

64
Q

how are kilovolts supplied across a tube?

A

step up transformer supplies a high voltage

65
Q

what is the effect of a higher kV?

A

greater potential difference across the x ray tube and so electrons will travel faster between the cathode and anode

66
Q

what does faster travel of electrons across the x ray tube due to higher kV mean?

A

electrons have more kinetic energy when they hit the anode and the resultant x rays will have higher energy

67
Q

what does kV affect?

A

quality (penetrating power) of the x rays produced

68
Q

what is the typical range of kV?

A

40-120 kV

69
Q

when does kV need to be increased?

A

in order to x ray thicker parts of the body

70
Q

what does an increase of 10 kV do to the exposure?

A

doubles it

71
Q

what does mA control do?

A

varies the small current (mA) which is heating the cathode

72
Q

what may mA be linked to in small machines?

A

kV so that overheating is avoided

73
Q

what does mA control?

A

cathode current - number of electrons being accelerated

74
Q

what is caused by increased mA?

A

cathode filament becomes hotter and more electrons become available to be accelerated across the tube

75
Q

what happens if more electrons hit the anode due to increased mA?

A

more x rays are produced

76
Q

does altering mA affect energy of x ray photons?

A

no - mA is independent of kV

77
Q

what is the timer used for?

A

time for device to close and therefore activate the high tension (kV) and filament (mA) circuits

78
Q

what does increasing the time of exposure result in?

A

increase in the number of x rays produced

79
Q

what governs the quality of x-rays produced?

A

mA and time

80
Q

what is mAs?

A

miliamps x exposure time in seconds

81
Q

what is the typical mA of a portable x ray machine?

A

20-60

82
Q

what is the typical mA of a fixed x ray machine?

A

1000

83
Q

when is an increase in mAs needed?

A

when radiographing thicker parts of the body

84
Q

what effect does doubling the mAs have on exposure?

A

doubles exposure

85
Q

what must be recorded during x ray process?

A

record exposure factors used

86
Q

why is it important to keep a record of exposure factors used?

A

see what factors worked / were appropriate
forms the basis for an exposure chart to guide future choices on animals of similar size - reducing unnecessary exposures

87
Q

what may happen with exposure factors in some lower output machines?

A
kA and mA may be linked (as one increases one must decrease)
fixed mA ( only kV and time can be changed)
88
Q

what machine settings must be decided on when setting up an exposure chart?

A

kV
mA
s - exposure time

89
Q

what other factors must be decided on when setting up an exposure chart?

A

distance
use of a grid
film or screen presentation of image

90
Q

how should an exposure chart be set up for a new machine?

A

take an x ray of the abdomen of a small to medium dog (cadaver) selecting exposure factors based on best guess adn previous image quality)
record the exposure factors used when you get a good x ray
measure the thickness of the dogs abdomen in cm

91
Q

how can an exposure chart be used to give exposure factors for other animals?

A

add or subtract kV for each cm more or less thickness when x raying a different animal

92
Q

does exposure vary between body parts?

A

yes

93
Q

what does kV need to be high enough to do?

A

penetrate thickness of tissue

94
Q

what is an increase in 10 kV equivalent to in mAs?

A

doubling mAs

95
Q

what must be kept constant for exposure chart to work?

A

x ray machine
film focal distance
digital detector
use or otherwise of grid

96
Q

what is the film focal distance?

A

distance from X-ray tube to x-ray image detector

97
Q

how will an underexposed image appear?

A

grainey

98
Q

how will an over exposed x ray appear?

A

very dark - unable to identify small structures

99
Q

what is the focal spot?

A

area of the anode ‘hit’ by electrons

100
Q

what size should the focal spot be?

A

as small as possible

101
Q

what is the best x ray image produced?

A

if there is a point source of x rays

102
Q

what is the issue with small focal spots?

A

difficulties with heat dissapation

103
Q

what focus options may be offered by some machines?

A

broad or fine focus

104
Q

what is fine focus used for?

A

smaller / thinner areas of anatomy

105
Q

what is the actual focal spot?

A

the target on the anode where the stream of electrons hits

106
Q

what is the effective focal spot?

A

source of the x ray beam

107
Q

how is the difference between the effective and actual focal spots produced?

A

the target on the anode is set at an angle to the stream of electrons allowing them to hit a larger area but make the x ray beam source smaller

108
Q

what does a smaller focal spot produce?

A

a sharper image

109
Q

why does a smaller focal spot produce a sharper image?

A

there is always a slight margin of blurring around the edge of a structure, the blurred margin is bigger with a large focal spot than with a small focal spot

110
Q

what is the penumbra?

A

slight margin of blurring at the edge of a structure when viewed on an x ray

111
Q

what does the x ray beam consist of a spectrum of?

A

different energies

112
Q

what is the issue with very low energy x rays?

A

have insufficient energy to penetrate the patient so are of no use in image formation but will still contribute to the negative x ray effects.

113
Q

how are low energy x-rays removed?

A

filtered out by a thin sheet of aluminium over the window of the x-ray tube

114
Q

describe portable x ray machines

A

small and compact
easy to move
low output

115
Q

what sort of exposures are often found on portable machines?

A

linked - operator doesn’t have total control of exposure factors

116
Q

why do portable x ray machines often have low output?

A

as they are operated from a normal electrical socket

117
Q

what is the difference between portable and mobile x ray machines?

A

mobile are larger and heavier - must be wheeled rather than carried

118
Q

what are mobile x ray machines operated from?

A

normal electrical socket

119
Q

how does the output of a mobile x ray machine compare to that of a portable machine?

A

mobile output is higher

120
Q

describe fixed x ray machines

A

permanent installations with x ray tube on a gantry

121
Q

where does the electrical supply for fixed x ray machines come from?

A

3 phase specialised electrical supply

122
Q

which type of x ray machine has the highest output?

A

fixed

123
Q

what is the mains voltage compensator?

A

adjustment of mains voltage by autotransformer so incoming voltage to kV is constant (fluctuations smoothed out)

124
Q

is the mains voltage converter usually automatic?

A

yes - except in very old machines

125
Q

what is the issue with mains supply voltage not being compensated?

A

mains supply varies in voltage, this would then vary the exposure of images and step up transformer would amplify variations

126
Q

what are the main controls seen on an x ray machine control panel?

A

kV control
mA control
timer

127
Q

what is used to prevent too high an exposure being used and damaging the machine?

A

internal interlocks

128
Q

how is mA controlled in portable machines?

A

fixed

linked to kV (one will increase and the other decrease)

129
Q

how is mA controlled in most mobile and all fixed machines?

A

independantly selected

130
Q

what is able to be altered in most x ray machines?

A

kV

131
Q

how is kV altered in machines where it is linked to mA?

A

altered with the same dial or as kV increases the fixed mA is decreased

132
Q

how is kV controlled in high powered machines?

A

kV and mA altered entirely independantly

133
Q

what does increasing the exposure time result in?

A

increased number of x rays produced as cathode is heated for longer, more electrons are produced and so more energy lost from them

134
Q

what must happen to the x ray beam?

A

limited or collimated to the area of the patient you are interested in

135
Q

what is the benefit of collimation?

A

reduces unnecessary radiation of patient

reduces the production of scattered radiation

136
Q

what is the benefit of reducing scattered radiation?

A

improved image quality

less exposure to staff remaining in the controlled area

137
Q

how is collimation achieved?

A

using a light beam diaphragm

138
Q

how does a light beam diaphragm work?

A

metal shutters alter aperture size through which primary beam will leave

139
Q

how is the collimated area shown?

A

light directed by mirrors through the aperture

140
Q

what are the key uses of the light beam diaphragm?

A

limiting x ray beam to necessary area

positioning of patient

141
Q

what is stated by the inverse square law?

A

the intensity of the x ray beam at a give point is inversely proportional to the square of the distance from the x ray tube

142
Q

why is the inverse square law important in radiation safety?

A

the further a person is from the x ray beam the less radiation they will receive and the safer they will be

143
Q

what is the effect of the inverse square law on exposure and x ray image quality?

A

distance between film and x ray tube should be constant so that there is a standard effect with given exposure settings

144
Q

define film focal distance

A

distance from the x ray tube to the x ray image receptor

145
Q

what must happen in FFD is altered?

A

mAs will need to be altered to produce a comparable radiograph

146
Q

how should a new mAs be calculated if film focal distance is altered?

A

old mAs x (new distance squared / old distance squared)

147
Q

define object film distance

A

distance between object being radiographed and the x ray detector

148
Q

what happens to an image if the object film distance is increased?

A

image will be magnified

sharpness of image decreased

149
Q

what can be done to keep magnification minimal?

A

keep patient / area of interest as close to the x ray cassette as possible

150
Q

what can be done is actual sizes of structures on x rays need to be known?

A

a marker of known size can be placed next to the anatomy in question during radiography and then the magnification of the item calculated so the anatomy size can be caluculated as well

151
Q

why does increasing OFD decrease sharpness of the image?

A

due to an increase in size of the penumbra around the edges

152
Q

how can distortion of an image be avoided?

A

keep the part of the patient to be imaged parallel to the x ray cassette and perpendicular to the x ray beam

153
Q

what are the 3 ways in which x rays may interact with matter?

A

x ray photons pass through unchanged
x ray photons are absorbed
x ray photons are scattered

154
Q

what is formed by x ray photons that pass through matter unchanged?

A

useful x-ray image

155
Q

what does the proportion of x ray photons absorbed depend on?

A

the nature of the material they are travelling through - this concept is essential for imaging

156
Q

what are the key factors which affect the absorption of x rays?

A

atomic number
physical density
thickness of tissues

157
Q

how does atomic number affect x ray absorption?

A

high atomic number leads to greater absorption of x rays

158
Q

how does physical density affect x ray absorption?

A

higher density leads to increased absorption of x rays

159
Q

how does tissue thickness affect x ray absorption?

A

thicker tissues lead to more absorption

160
Q

what does the x ray image depend on?

A

differential absorption of x rays by different tissues in the body

161
Q

why does bone appear white on x ray?

A
high Z (atomic number)
good absorber
162
Q

why does gas appear black on x ray?

A

low density, poor absorber

163
Q

why does soft tissue appear grey on x ray?

A

intermediate Z and density so intermediate absorber

164
Q

what are the key issues associated with scattered x ray photons?

A
move in random directions
lose energy
not useful in image formation
degrades quality of image
radiation hazard
165
Q

what is the purpose of x ray grids?

A

minimise effect of scatter on image and improve image quality by reducing the amount of scattered radiation reaching the film

166
Q

when are grids useful?

A

when radiographing thicker areas (>10cm)

167
Q

where are grids placed?

A

between patient and cassette

168
Q

what are grids made from?

A

;/./flat plates consisting of a series of thin strips of lead alternating with thin radiolucent strips

169
Q

what are the radiolucent strips in grids formed from?

A

plastic of aluminium

170
Q

what is the purpose of lead strips within grids?

A

designed to absorb most of the scattered radiation which hits the grid in all directions

171
Q

what is the purpose of radiolucent strips within a grid?

A

designed to allow the primary beam through (as it travels in a straight line)

172
Q

why are higher exposure factors (mAs) needed if using a grid?

A

some scattered radiation will manage to pass through the spacing material and some of the primary beam will be absorbed by the lead

173
Q

what is the grid ratio?

A

height of the lead strips divided by the width of the spacing material

174
Q

what are typical grid ratios?

A

6:1 and 12:1

175
Q

what type of grids are more efficient at removing scatter?

A

higher ratio

176
Q

what is the issue with higher ratio grids?

A

remove more of the primary beam so a higher exposure is needed

177
Q

how does lead strips per cm affect scatter and exposure?

A

more scatter is removed by more strips of lead per cm but more of the primary beam is absorbed too so higher exposure is needed

178
Q

what is the grid factor?

A

number by which the mAs must be multiplied if a grid is used

179
Q

what does the grid factor depend on?

A

grid ratio

lines per cm

180
Q

what are the types of grid?

A
parallel
focused
pseudo-focussed
cross hatched
moving / Potter Bucky
181
Q

describe the lead strips within a parallel grid

A

parallel and of equal height

182
Q

what effect will a parallel grid have on the primary beam?

A

some increase in the amount of primary beam absorbed towards the edge of the grid as the beam diverges

183
Q

what are the benefits of parallel grids?

A

cheap and easy to use

can be used either way up and at any FFD or centering point

184
Q

describe the layout of a focused grid

A

lead strips slope progressively more towards the periphery of the grid which mimics the divergence of the x ray beam so there is no image cut off towards the edges

185
Q

how must a focused grid be used?

A

the correct way up - due to angling of lead

centre of x ray beam must be at the centre of the grid and an appropriate FFD used

186
Q

what is a disadvantage of focused grids over parallel?

A

more expensive

187
Q

describe pseudo-focused grids

A

lead strips are parallel to each other but the height reduces progressively towards the periphery of the grid to accommodate dispersion of the primary beam

188
Q

what is the most efficient type of grid?

A

cross hatched

189
Q

describe the layout of a cross hatched grid

A

two sets of lead strips at right angles to each other

190
Q

what are the disadvantages of cross hatched grids?

A

require high exposures, accurate centering and are expensive

191
Q

describe the layout of moving / Potter Bucky grids

A

parallel grids mounted permanently beneath a radiolucent x ray table top. These oscillate rapidly to and fro during exposure

192
Q

what are the benefits of moving / Potter Bucky grids?

A

fine lines which appear on the image when a stationary grid are blurred out and not seen

193
Q

does a moving / Potter Bucky grid affect image quality?

A

no - cassette / detector is beneath the moving grid and stays stationary so image remains sharp

194
Q

historically how was the x ray image recorded?

A

on x ray film

195
Q

how are almost all x ray images recorded now?

A

digital radiography

196
Q

are the x ray machine and table different in digital imaging systems?

A

essentially unchanged

197
Q

what are the 2 types of image receptor used in digital imaging?

A

storage phosphor cassette (CR)

flat panel detector (DR)

198
Q

what is used to capture the image in computed radiography (CR)?

A

cassettes similar to conventional film / screen casettes

199
Q

what is contained within cassettes for computed radiography?

A

storage phosphor plate

200
Q

how is an image produced by CR digital imaging?

A

energy from interactions with the x ray beam is stored in the plate
energy is later released as light when the phosphor is excited by a laser beam in the plate reader
light released from the plate is captured and quantified by photomultiplier tubes
converted to electrical signal and then to an image on a screen

201
Q

can CR phosphor plates be reused?

A

yes

202
Q

how can CR plates be reused?

A

phosphor plate is erased by bright light

203
Q

what should happen to CR phosphor plates if they have been unused for a period of time?

A

erased before use

204
Q

how long does the imaging process in CR take?

A

around 1-2 mins

205
Q

how is the CR plate read when in the cassette reader?

A

one line at a time

206
Q

how is the image produced in direct digital systems (DR)?

A

electronic detector plate directly captures the x ray image
attached to the computer via cable link (or some by wi-fi)
image is displayed immediately on monitor

207
Q

describe the process of acquiring a digital x ray image

A

enter patient information (accurate and complete)
select anatomical region of interest
select animal size

208
Q

why must the correct anatomical region of interest be selected during digital x ray?

A

processing algorithms will vary and formulae will adjust / reconstruct images based on the expected tissue types in that area

209
Q

with both CR and DR systems what is shown after each exposure?

A

exposure index - applies numerical value to exposure (name varies between manufacturers)

210
Q

what must you be aware of about your own machines exposure index?

A

whether it is proportional or inversely proportional to measure of exposure

211
Q

how are grey scale values in digital images determined?

A

‘look up tables’

212
Q

how do ‘look up tables’ work

A

input pixel intensity is mapped to an output greyscale value

213
Q

what can grey scale values compensate for?

A

overexposure

214
Q

what can be done with digital x ray images that cannot be done with conventional radiographic film?

A

manipulate image to show detail

215
Q

how can digital images be manipulated?

A
filters / algorithms 
contrast / brightness
size
orientation
annotation and measurement
216
Q

what filters may be used on digital images?

A

edge enhancement

contrast enhancement

217
Q

how are digital images stored?

A

computer files

218
Q

what format are images stored in?

A

dicom (.dcm)

219
Q

what does Dicom stand for?

A

digital imaging and communications in medicine

220
Q

how often should images be backed up?

A

daily

221
Q

what are the issues with printing digital images onto paper/film?

A

would increase cost

loss of detail

222
Q

what software is used for storing images long term?

A

PACS - picture archiving and communication system

223
Q

what is the purpose of storage software such as PACS?

A

facilitates identification, manipulation, backup and retrieval of images

224
Q

what are the advantages of digital radiography?

A

decreased running costs
time saving especially DR (reduced repeat rate)
reduced radiation dose due to reduced repeats
improved images in some cases due to digital filters
easy retrieval and storage
easy communication of images
portable instant images

225
Q

what are the disadvantages of digital radiography?

A

set up costs
viewing of images is limited by computer availability
specific artifacts
ensuring adequate back up of files is essential

226
Q

what is a satisfactory radiograph said to be?

A

diagnostic

227
Q

what image quality factors can be assessed?

A
opacity 
contrast
sharpness
patient positioning
centering of x ray beam
collimation of x ray beam
228
Q

what does radiographic opacity describe?

A

how black and white the image is overall

229
Q

what does radiographic contrast describe?

A

differences between black, white and grey in adjacent areas

230
Q

what does radiographic sharpness describe?

A

clarity of the image

231
Q

what is radiographic opacity?

A

degree of blackening of the radiographu

232
Q

what colour do radiopaque tissues appear?

A

white

233
Q

what colour do radiolucent tissues appear?

A

black

234
Q

what influences radiographic opacity?

A

patient (tissue type being imaged and thickness)
exposure factors
digital algorithm / processing

235
Q

when will opacity of a digital image vary?

A

not much with differing exposures unless the image is markedly exposed
may vary with algorithm used (e.g. thorax or abdomen)

236
Q

can radiographic opacity be manipulated post exposure?

A

yes using region of interest settings

237
Q

what is radiographic contrast?

A

difference in radiographic opacity between adjacent areas of the image

238
Q

what does a long scale of contrast show on a digital radiograph as?

A

many shades of grey

239
Q

what does a short scale of contrast show on a digital radiograph as?

A

black and white (not much grey)

240
Q

what does radiographic contrast depend on?

A

the inherent contrast of the part of the patient being radiographed
the digital algorithm being selected
the amount of scatter reaching the film

241
Q

what does the inherent contrast of the part being radiographed depend on?

A

atomic number of tissue

density of the tissue

242
Q

what does scatter produce on film?

A

overall blackning of film

243
Q

where is more scatter generated from?

A

thicker areas of tissue and larger areas of collimation

244
Q

how can scatter be minimised?

A

collimation (reduce primary beam size)

using a grid when radiographing large parts

245
Q

what is radiographic sharpness?

A

the ability to distinguish fine detail on an image

246
Q

what is radiographic sharpness decreased by?

A

movement (animal, table and x ray tube)
scattered radiation
object film distance

247
Q

how does object film distance affect sharpness?

A

increase in penubra and magnification with increased object film distance

248
Q

what technique faults can affect radiographs?

A
poor positioning / centering
inadequate numbers of projections
no right / left markers
no patient ID / date
movement blur
incorrect use of grid leading to grid cut off
249
Q

what technical radiography issue is seen in this image?

A

focused grid placed the wrong way up - grid cut off

250
Q

what miscellaneous artefacts can be seen on radiographs?

A
double exposure
digital exposure errors
'uberschwinger' effect
ghost artefact
moire artefact
dirt on light guide
251
Q

what happens during double exposure artefact?

A

2 exposures on 1 detector - not seen on DR

252
Q

what artefact is shown in this image?

A

double exposure

253
Q

what artefact is shown in this image?

A

digital underexposure

254
Q

what artefact is shown in this image?

A

over exposure

255
Q

when does Uberschwinger or rebound artefact occur?

A

when there is a large density difference between adjacent objects - excessive edge enhancement by computer algorithm

256
Q

what artefact is shown in this image?

A

Uberschwinger or rebound artefact

257
Q

when is Uberschwinger or rebound artefact commonly seen?

A

around orthopedic implants

258
Q

what does Uberschwinger or rebound artefact look like?

A

implant loosening

259
Q

how can Uberschwinger or rebound artefact be differentiated from implant loosening?

A

artefact will continue into soft tissues whereas losening will not

260
Q

what causes ghost artefact?

A

incomplete erasure of a CR plate before use

also seen if a CR plate is exposed to light

261
Q

what artefact is shown in this image?

A

ghost artefact

262
Q

what causes Moire artefact?

A

arise with CR systems due to interference between the frequency of the laser reader and the number of lines per centimeter in the grid

263
Q

how is Moire artefact overcome?

A

rotate grid by 90 degrees or chnge

264
Q

how does Moire artefact appear?

A

bands across the image

265
Q

what artefact is shown in this image?

A

Moire

266
Q

what artefact is shown in this image?

A

dirt on light guide

267
Q

when does dirt on light guide occur?

A

emitted light blocked by dirt from reaching the photomultiplier tube

268
Q

how does dirt on light guide appear on a the radiograph?

A

line along image orientated in the direction the imaging plate moves during the reading process

269
Q

how can dirt on light guide be prevented?

A

CR plate reader cleaning and maintenance should be performed routinely

270
Q

what is the main piece of legislation governing radiography in a veterinary practice?

A

ionising radiation regulations 2017

271
Q

what are the 3 basic principles of safe x rays?

A

the radiograph should only be taken if there is a clinical reason
exposure of personnel should be kept to a minimum
no dose limits should be exceeded

272
Q

what is the key effect of ionising radiation?

A

damages living tissue (cells)

273
Q

what are the 3 key effects of ionising radiation?

A

carcinogenic
somatic
genetic / mutation

274
Q

what are the carcinogenic effects of ionising radiation?

A

tumor development in cells that have been exposed to radiation

275
Q

what are the somatic effects of ionising radiation?

A

direct changes in body tissues that occur not long after exposure has occurred (e.g. radiotherapy effects)

276
Q

what are the genetic / mutation effects of ionising radiation?

A

occur when gonads are irradiated and mutations occur in the chromosomes, May give rise to abnormalities in offspring

277
Q

what are the main sources of radiation hazard?

A

tube head
primary beam
scatter

278
Q

what happens to the intensity of scatter as it moves away from the source?

A

reduces in intensity

279
Q

how can scattered radiation be reduced?

A
tight collimation
reduced exposure factors (as much as possible)
PPE used
lead cover on table
rotation of staff
280
Q

what are the general requirements if a practice intends to use x rays?

A

HSE must be notified
practice must appoint radiation protection supervisor (RPS)
radiation protection advisor (RPA) will be appointed

281
Q

who draws up the local rules and system of work relating to ionising radiation safety?

A

RPA

282
Q

what do local rules around ionising radiation ensure?

A

no animal is manually restrained
no unnecessary personnel in room during exposure
suitable protection is used
there are guidelines for pregnant staff members
minimum age of 16 yrs for trainee staff
areas within practice for x rays are classified
guidelines for implementation of warning signs during exposure

283
Q

what is the ionising radiation system of work prepared by?

A

RPA and RPS

284
Q

where should the ionising radiation systems of work be displayed?

A

whenre everyone can access and read them

285
Q

what information is included in the system of work?

A

SOP for x rays
RPS details
description of restricted areas
what todo in the event of an accident

286
Q

where is the controlled area defined as?

A

area where radiation dose will exceed 7.5 mSv/h

287
Q

where is the controlled area usually located?

A

specific room

288
Q

how large should the controlled area be?

A

large enough for 2 people to be 2m away from primary beam (or able to exit room)

289
Q

how can the controlled area be identified?

A

warning signs

290
Q

what can indicate that an exposure is being taken?

A

light
use of voice
beep

291
Q

how are personnel protected?

A

minimum time taking radiographs and staff rotated
staff 2m from primary beam, leave the room where possible, never hold the patient
use of barriers e.g. lead gloves, aprons and thyroid protectors. Lead glass, lead plywood doors, lead sheeting/barium plaster on walls

292
Q

what considerations must be made to ensure PPE is functional?

A

hung up properly (no folding)

should be regularly x rayed to chack integrity

293
Q

what are dose limits set to do?

A

protect workers and members of the public from the effects of ionising radiation

294
Q

what level are dose limits set at?

A

one which balance the risk from exposure with the benefits of ionising radiation

295
Q

what are the different classes of people who have different dose limits?

A

adult employees aged 18 or over
trainees aged 16 to 18
any other person, such as a member of the public

296
Q

what enables detection of radiation to take place?

A

dosimeters must be worn by staff

297
Q

what are the 2 types of dosimeters?

A

film badges

thermoluminescent detectors

298
Q

how do film badges detect radiation dose?

A

contain a small piece of film processed photographically. Film blackening is proportional to exposure

299
Q

how do thermoluminescent detectors detect radiation exposure?

A

small crystal of lithium heparin absorbs radiation. When heated the TLD emits light, the amount of light emitted is compared to a standard, known radiation dose

300
Q

how long are dosimeter worn for?

A

4, 8 or 12 weeks

301
Q

where are dosimeters returned to to be read and reported on?

A

national radiation protection board

302
Q

can dosimeter badges be shared?

A

no - everyone must have their own

303
Q

where must badges only be worn?

A

at work, at waist level under lead apron

304
Q

what must dosimeters be protected from?

A

water
excessive heat
physical damage

305
Q

who should read the dosimeter report from the NRPB?

A

RPS or practice manager

306
Q

how long must dosimeter records be kept for?

A

2 years

307
Q

what are contrast media?

A

agents that are more or less opaque than surrounding tissue

308
Q

what do contrast media do?

A

delineate organs / cavities within the body

309
Q

what is the purpose of contrast media?

A

to see structures not normally visible or poorly visible

to gain more information about soft tissue structures

310
Q

what are the 2 key types of contrast media?

A

positive contrast

negative contrast

311
Q

what colour does positive contrast appear as on radiographs?

A

white

312
Q

why does positive contrast appear white on radiographs?

A

due to its high atomic number - absorbs x ray beam

313
Q

give 2 examples of positive contrast media

A

barium

iodine

314
Q

what is used for negative contrast?

A

a gas (air or CO2)

315
Q

what colour does negative contrast show up as on x ray?

A

black

316
Q

why does negative contrast media show as black on x ray?

A

low density - doesn’t stop x rays

317
Q

what area of the body is barium used to study?

A

GI tract

318
Q

in what formulations may barium be supplied?

A

powder

suspension

319
Q

why is barium a good contrast medium?

A
inert
non - toxic
reasonably palatable
cheap
good mucosal detail
no osmotic effect
320
Q

why is it important that barium has a low osmotic effect?

A

so that it is not diluted during it’s movement through the GI tract

321
Q

aside from barium what is used as positive contrast?

A

water soluble iodine-containing preparations

322
Q

what are the 2 main groups of iodine contrast media?

A

ionic

non-ionic

323
Q

how is iodine introduced into the body for a contrast study?

A

IV

324
Q

how is iodine eliminated from the body after a contrast study?

A

renal excretion

325
Q

what are 2 examples of ionic iodine contrast?

A

urografin 150

conray 420

326
Q

what are 2 examples of non-ionic iodine contrast?

A

omnipaque 300

Niopam

327
Q

what does the number following the name of the iodine contrast relate to?

A

how many mg of iodine there are per ml of solution

328
Q

what are the disadvantages of ionic water-soluble iodinated contrast media?

A
irritant extravascularly
toxic in large doses
viscous
contraindicated IV in patients with cardiovascular or renal insufficiency
contraindicated for mylography
329
Q

how can the viscosity of ionic water-soluble iodinated contrast media be reduced?

A

warming before use

330
Q

why is ionic water-soluble iodinated contrast media contraindicated for myelography?

A

involves interaction with subarachnoid space

331
Q

what studies can non-ionic water-soluble iodinated contrast media be used for?

A

all

332
Q

what are the disadvantages of non-ionic water-soluble iodinated contrast media?

A

slightly more expensive
viscous
side effects can still occur although are rare

333
Q

what are the side effects associated with water-soluble iodinated contrast media?

A
anaphylaxis
nephrotoxicity
urticaria
vomiting
pyrexia
334
Q

what are the advantages of negative contrast media?

A

cheap (free!)
simple to use
relatively safe
can combine with positive contrast agents for double contrast studies

335
Q

what are the disadvantages of negative contrast media?

A

very small risk of air embolism
poor mucosal detail
produce less contrast than positive contrast agents

336
Q

how can the risk of air embolism when using negative contrast studies be reduced?

A

perform study in left lateral recumbancy rather than right

337
Q

what must be considered before contrast radiography is used?

A
indications - will lesion be shown
time involved
cost
correct preparation of patient (enema / feeding)
restraint needed
338
Q

what type of radiograph must be taken before contrast is used?

A

plain

339
Q

why must plain radiographs be taken before contrast is used?

A

check radiographic quality (e.g. positioning, exposure factors)
check patient preparation
look for diagnosis to check if contrast is necessary
look for radiopaque lesions that may be obscured by positive contrast

340
Q

what is the safest way of dosing contrast for cystography?

A

palapation of bladder during study to see how filled it is becoming

341
Q

what has replaced many contrast GI studies?

A

endoscopy

342
Q

what is often used to diagnose PSS or for urinary tract investigations?

A

ultrasound

343
Q

what studies have replaced myelography?

A

CT and MRI (although CT still uses contrast in some cases)

344
Q

what are the indications for barium swallow?

A

dysphagia
regurgitation
suspected rupture

345
Q

what anatomy is shown by a barium swallow?

A

pharynx and oesophagus

346
Q

what forms of barium can be administered for a barium swallow?

A

liquid barium and/or barium food

347
Q

what type of contrast should be used if oesophageal rupture is suspected?

A

iodinated contrast

348
Q

when must care be taken when administering barium?

A

if there is swallowing issues, respiratory distress or animal is weak - aspiration risk

349
Q

what does a barium ‘follow through’ study evaluate?

A

stomach and small intestine

350
Q

in what form is barium given in a ‘follow through’ study?

A

liquid via mouth or stomach tube

351
Q

when are radiographs taken during a barium ‘follow through’ study?

A

immediately then at intervals depending on transit time until barium is in colon / 24 hours reached

352
Q

what techniques have largely superseded barium ‘follow through’ studies?

A

ultrasound and endoscopy

353
Q

what is evaluated by a barium enema?

A

large intestine

354
Q

how is barium introduced into the large intestine?

A

liquid barium infused into rectum post-enema

can be followed with air for double contrast

355
Q

what are the main issues with barium enema?

A

messy and difficult to interpret

356
Q

when may a small volume of contrast in the colon be useful?

A

to identify colon if unclear on radiograph

357
Q

what other techniques can be used in place of barium enema?

A

endoscopy

assessment of colonic wall by ultrasound

358
Q

what are the main complications of a barium enema?

A

leakage
overinflation with air leading to rupture
both rare

359
Q

what contrast studies are used in the urinary tract?

A

IV urography
cystography
urethrography

360
Q

what contrast medium must be used in the urinary tract?

A

water-soluble iodinated contrast media NEVER barium

361
Q

why can’t barium be used in studies of the urinary tract?

A

cannot be given IV as no suspension

irritant in bladder that can lead to granulomatous cystitis

362
Q

what is excretory urography used for?

A

identify and assess kidneys
assess ureters
assess vesicoureteral junction

363
Q

where is contrast given during excretory urography?

A

bolus of contrast into peripheral vein

364
Q

when are radiographs taken during excretory radiography?

A

immediately
5 mins
10 mins
15 mins

365
Q

what type of radiograph is taken immediately after injection of contrast for excretory urography?

A

nephrogram - VD

366
Q

what type of radiograph is taken 5 mins after injection of contrast for excretory urography?

A

pyelogram (renal pelvis) - VD

367
Q

what type of radiograph is taken 10 mins after injection of contrast for excretory urography?

A

ureterogram - lateral

368
Q

what type of radiograph is taken 15 mins after injection of contrast for excretory urography?

A

ureterovesicular junction - lateral

369
Q

what is shown during cystography?

A

delineates bladder

370
Q

how is contrast introduced during cystography?

A

urinary catheter

371
Q

what happens during pneumocystogram?

A

air introduced into the bladder only

372
Q

what is shown during pneumocystogram?

A

bladder location
large masses
marked thickening

373
Q

what contrast is used during a positive contrast cystogram?

A

iodinated contrast

374
Q

what does a positive contrast cystogram show?

A

leakage and location

375
Q

what contrast is used during double contrast cystogram?

A

both agents - positive and negative

376
Q

what is shown during double contrast cystograms?

A

delineation of wall and content of bladder

377
Q

what is shown in a vagino-urethrography?

A

urethra and vagina

378
Q

what contrast medium is used during vagino-urethrography?

A

water soluble iodinated contrast medium

379
Q

how is contrast media introduced into the urethra / vestibule during vaginourethrography?

A

via foley catheter

380
Q

what is a possible complication arising from vaginourethrography?

A

urethral damage due to over distention and damage from catheter

381
Q

what is shown during myelography?

A

delineates subarachnoid space and localises lesions of the spinal cord

382
Q

what contrast medium must be used for myelography?

A

non-ionic water soluable contrast media

383
Q

why must non-ionic water soluable contrast media be used in myelography?

A

ionic can cause seizures / arachnoiditis

384
Q

what has largely replaced myelography?

A

CT and MRI

CT myelography is still performed

385
Q

how must the patients head be kept during recovery from myelography?

A

elevated

386
Q

why must the patients head be kept elevated during recovery from myelography?

A

due to nature of contrast media, even though it causes minimal neurotoxicity, it must be prevented from entering the brain as this could cause the patient to seize

387
Q

what must be available at all times during myelography?

A

patent IV catheter

IV diazepam

388
Q

what is shown during angiography?

A

blood vessels

389
Q

what is shown during arthrography?

A

joints

390
Q

what is shown during fistulography?

A

sinus tracts

391
Q

what must happen if any positive contrast media is spilled?

A

it is wiped up otherwise artefacts will appear on the developed radiograph

392
Q

what checks must be made before taking an exposure?

A

correct animal
decide on projections needed
select exposure facts / grid
ensure animal is placed over cassette or grid
appropriate centering and and collimation

393
Q

what is positioning?

A

the use of pads, wedges, sandbags and ties to ensure that the animal is straight and restrained for the examinatio

394
Q

what is centring?

A

using the light beam diaphragm, the primary beam is positioned directly over the correct surface landmark for the examination

395
Q

what are the only x rays that should be taken?

A

only films that are clinically indicatd

396
Q

under what circumstances may an individual be able to remain in the room during an exposure?

A

holding cassettes for equine imaging
inflating chest
injecting contrast

397
Q

what should be worn if someone is within the room during x ray exposure?

A

lead PPE

398
Q

what is the role of lead protection?

A

protects against scattered radiation

399
Q

what must be considered when using a horizontal beam?

A

the walls and what is beyond the room as radiation doesn’t stop at x ray cassette

400
Q

what can be done to enure x rays don’t pass through the wall when a horizontal beam is used?

A

double brick equivilent
lead screen
barium plaster

401
Q

how can an animal be restrained for imaging?

A

GA
sedation
positioning aids

402
Q

why is patient restraint essential?

A

to prevent low quality or non diagnostic images

403
Q

what is the role of positioning aids?

A

maintain appropriate position for capture of radiograph

404
Q

what positioning aids are useful for VD/DV exposures?

A

troughs

405
Q

what can troughs be formed from?

A

radiolucent foam or plastic

406
Q

what can be used to support different areas of anatomy?

A

foam pads and wedges

407
Q

what must happen to foam pads and wedges if they come into contact with contrast medium?

A

washed

408
Q

why must care be taken when using sandbags to position a patient for x ray?

A

sand is radiopaque so will be seen on the image if in the collimated area

409
Q

what can be used to tie legs?

A

tapes

rope ties

410
Q

what additional equipment may be used when imaging horses?

A

positioning blocks
cassette holders
rope head collar for imaging of head

411
Q

what must you be aware of on cats and dogs that can interfere with x ray image?

A

collars and harnesses

412
Q

when should ties only be used?

A

when an animal is under GA so won’t wake up

413
Q

when is care needed with positioning?

A

injured or debilitated patients

414
Q

what should be avoided while x raying?

A

loud noises or sudden movements

415
Q

what are markers used for during x rays?

A

identifying included area of anatomy, limb, side or recumbancy of the patient

416
Q

what is the minimum information that should be put on an x ray film?

A

animals name
owner surname
date

417
Q

when should identification be on film?

A

before processing or saving image

418
Q

how is patient identification placed on an image within a digital system?

A

entered first before any images taken

419
Q

how is patient identification placed on an image in conventional film?

A

x-rite tape

actinic (light marker)

420
Q

what should you check when assessing the radiograph?

A
identification present and correct
markers and legends visible and correct
area under examination shown
correct projection taken
suitable exposure factors used
adequate contrast, density and sharpness
collimation visible but not too tight
are artifacts obscuring anything important
421
Q

what are the critical decisions to be made when assessing the radiograph?

A

any repeats needed

any further views needed

422
Q

when naming projections what is described?

A

path of the x ray beam from the x ray tube to the image receptor

423
Q

what will also be provided by projection name?

A

information about the position of the animal (e.g. ventrodorsal - on their back)

424
Q

what are lateral projections named after?

A

the side the animal is lying on

425
Q

how can image magnification be minimised?

A

body close to cassette

426
Q

why does the body need to be parallel to the cassette?

A

minimise distortion

Decks in X Clinical Veterinary Nursing Theory Class (70):