Diagnostic Imaging - X-Ray Flashcards
what does the electromagnetic spectrum consist of?
a number of different types of waves including radiowaves, visible light and X-rays
do all waves on the electromagnetic spectrum travel at the same speed?
yes- speed of light
in what direction do all waves from the electromagnetic spectrum travel?
in a straight line
what is energy inversely proportional to?
wavelength
describe the energy and wavelength of X-rays
high energy
shorter wavelength
what is the wavelength?
the distance between two consecutive peaks or troughs of a wave
what is the frequency of the electromagnetic spectrum?
number of times a peak passes a fixed point per second
what is the frequency of a wave an indicator of?
the energy of a wave
how are frequency and wavelength related?
inverse relationship - as one increases the other will decrease
describe the wavelength and frequency of X rays
short wavelength and high frequency
how much energy do x rays have?
high - due to high frequency
what is in the nucleus of an atom?
positively charged protons and neutral neutrons
what surrounds the nucleus of an atom?
electrons (negatively charged)
what makes an atom electronically neutral?
number of protons = number of electrons
what is the atomic number of an element?
the number of protons (Z)
what is the atomic weight of an element?
number of protons plus number of neutrons
what does a high atomic number mean in terms of x ray production?
high x ray production
how are x-rays produced?
interaction of fast moving electrons with a metal traget
when are x rays used?
radiography
when are gamma rays produced?
decay of radioactive elements
when are gamma rays used?
nuclear medicine (scintigriphy)
what are the 2 main components of the x ray tube?
cathode assembly
anode assembly
what charge does the anode have?
positive
what charge does the cathode have?
negative
what is the cathode?
a wire filament made of tungsten
what happens when a small electrical current is passed through the cathode filament?
it heats up
what is caused by the cathode filament heating up?
a cloud of free electrons form around the wire
what is thermionic emission?
heating and the associated release of electrons
what is used to keep the cloud of electrons together near the cathode?
focussing cup
why is the focusing cup near the cathode necessary?
electrons would naturally be repelled by the cathode
what is found on the anode?
tungsten target
why is tungsten used?
it has a high atomic number and so is efficient at producing x rays
why is it necessary for tungsten to have a high melting point?
most of the energy produced is heat
what happens when potential difference is applied across the tube?
electrons hit the target of the anode at speed and produce x-rays
how is a potential difference applied across the x-ray tube?
the circuit is closed
what are the 2 mechanisms of x ray formation?
general emission
charactoristic emission
how are x rays formed during general emission?
rapid deceleration of electrons as they meet tungsten atoms causes energy to be released as x rays
how are x rays produced during characteristic emission?
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
which is the main mechanism of x ray formation?
general emission
what is the energy produced by characteristic emission specific to?
the atom in use (e.g. tungsten has level of energy that will be produced0
is the production of x rays efficient?
no - majority of energy produced is heat (99%)
what is the focal spot?
small area of the anode where electrons from the cathode are focussed
what is the key issue when x -rays are being produced?
ensuring that heat is dissapated
what are the 2 types of anode?
stationary
rotating
where is the tungsten target located in the stationary anode?
in a block of copper
what is the benefit of embedding the tungsten target in copper in a stationary anode?
alows conduction of heat away from target
describe a rotating anode
anode is a disc with an angled edge - tungsten track runs around the angled edge
what is the disc of the rotating anode mounted on?
molybdenum rod
what is the disc of a rotating anode rotated by?
electric motors
what is the purpose of the molybdenum rod found in rotating anodes?
poor heat coordinator
how is heat lost from the rotating anode?
radiation and convection from the surface of the disc
how is heat produced around circumference of the disc rather than a single point?
cathode is offset and targets the edge of the disc
what are the anode and cathode placed in?
evacuated (vacuum) pyrex tube
why do the anode and cathode need to be within a vacuum?
prevents interference of gas with the electrons
what is the pyrex tube containing the anode and cathode immersed in?
oil - to aid heat conduction and electrical insulation
what is the x ray tube surrounded by?
lead, to prevent x rays from escaping, apart from a small window through which the useful x ray beam emerges
what are the 3 main specifications used during x ray?
exposure factors
focal spot
filtration
what does the focal spot contribute to?
quality of image
how are exposure factors altered?
via the control panel of the x ray machine
what are the settings that contribute to exposure factors?
on/off button
kV control
mA cntrol
timer
what happens when an x ray machine is connected to a power supply?
the area around it is considered in law as a ‘controlled area’ with associated access restrictions
why is it important to know the location of the mains power switch?
disconnecting the machine from the mains in an emergency will stop the emission of radiation
what does kV stand for?
kilovalots
how are kilovolts supplied across a tube?
step up transformer supplies a high voltage
what is the effect of a higher kV?
greater potential difference across the x ray tube and so electrons will travel faster between the cathode and anode
what does faster travel of electrons across the x ray tube due to higher kV mean?
electrons have more kinetic energy when they hit the anode and the resultant x rays will have higher energy
what does kV affect?
quality (penetrating power) of the x rays produced
what is the typical range of kV?
40-120 kV
when does kV need to be increased?
in order to x ray thicker parts of the body
what does an increase of 10 kV do to the exposure?
doubles it
what does mA control do?
varies the small current (mA) which is heating the cathode
what may mA be linked to in small machines?
kV so that overheating is avoided
what does mA control?
cathode current - number of electrons being accelerated
what is caused by increased mA?
cathode filament becomes hotter and more electrons become available to be accelerated across the tube
what happens if more electrons hit the anode due to increased mA?
more x rays are produced
does altering mA affect energy of x ray photons?
no - mA is independent of kV
what is the timer used for?
time for device to close and therefore activate the high tension (kV) and filament (mA) circuits
what does increasing the time of exposure result in?
increase in the number of x rays produced
what governs the quality of x-rays produced?
mA and time
what is mAs?
miliamps x exposure time in seconds
what is the typical mA of a portable x ray machine?
20-60
what is the typical mA of a fixed x ray machine?
1000
when is an increase in mAs needed?
when radiographing thicker parts of the body
what effect does doubling the mAs have on exposure?
doubles exposure
what must be recorded during x ray process?
record exposure factors used
why is it important to keep a record of exposure factors used?
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
what may happen with exposure factors in some lower output machines?
kA and mA may be linked (as one increases one must decrease) fixed mA ( only kV and time can be changed)
what machine settings must be decided on when setting up an exposure chart?
kV
mA
s - exposure time
what other factors must be decided on when setting up an exposure chart?
distance
use of a grid
film or screen presentation of image
how should an exposure chart be set up for a new machine?
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
how can an exposure chart be used to give exposure factors for other animals?
add or subtract kV for each cm more or less thickness when x raying a different animal
does exposure vary between body parts?
yes
what does kV need to be high enough to do?
penetrate thickness of tissue
what is an increase in 10 kV equivalent to in mAs?
doubling mAs
what must be kept constant for exposure chart to work?
x ray machine
film focal distance
digital detector
use or otherwise of grid
what is the film focal distance?
distance from X-ray tube to x-ray image detector
how will an underexposed image appear?
grainey
how will an over exposed x ray appear?
very dark - unable to identify small structures
what is the focal spot?
area of the anode ‘hit’ by electrons
what size should the focal spot be?
as small as possible
what is the best x ray image produced?
if there is a point source of x rays
what is the issue with small focal spots?
difficulties with heat dissapation
what focus options may be offered by some machines?
broad or fine focus
what is fine focus used for?
smaller / thinner areas of anatomy
what is the actual focal spot?
the target on the anode where the stream of electrons hits
what is the effective focal spot?
source of the x ray beam
how is the difference between the effective and actual focal spots produced?
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
what does a smaller focal spot produce?
a sharper image
why does a smaller focal spot produce a sharper image?
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
what is the penumbra?
slight margin of blurring at the edge of a structure when viewed on an x ray
what does the x ray beam consist of a spectrum of?
different energies
what is the issue with very low energy x rays?
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.
how are low energy x-rays removed?
filtered out by a thin sheet of aluminium over the window of the x-ray tube
describe portable x ray machines
small and compact
easy to move
low output
what sort of exposures are often found on portable machines?
linked - operator doesn’t have total control of exposure factors
why do portable x ray machines often have low output?
as they are operated from a normal electrical socket
what is the difference between portable and mobile x ray machines?
mobile are larger and heavier - must be wheeled rather than carried
what are mobile x ray machines operated from?
normal electrical socket
how does the output of a mobile x ray machine compare to that of a portable machine?
mobile output is higher
describe fixed x ray machines
permanent installations with x ray tube on a gantry
where does the electrical supply for fixed x ray machines come from?
3 phase specialised electrical supply
which type of x ray machine has the highest output?
fixed
what is the mains voltage compensator?
adjustment of mains voltage by autotransformer so incoming voltage to kV is constant (fluctuations smoothed out)
is the mains voltage converter usually automatic?
yes - except in very old machines
what is the issue with mains supply voltage not being compensated?
mains supply varies in voltage, this would then vary the exposure of images and step up transformer would amplify variations
what are the main controls seen on an x ray machine control panel?
kV control
mA control
timer
what is used to prevent too high an exposure being used and damaging the machine?
internal interlocks
how is mA controlled in portable machines?
fixed
linked to kV (one will increase and the other decrease)
how is mA controlled in most mobile and all fixed machines?
independantly selected
what is able to be altered in most x ray machines?
kV
how is kV altered in machines where it is linked to mA?
altered with the same dial or as kV increases the fixed mA is decreased
how is kV controlled in high powered machines?
kV and mA altered entirely independantly
what does increasing the exposure time result in?
increased number of x rays produced as cathode is heated for longer, more electrons are produced and so more energy lost from them
what must happen to the x ray beam?
limited or collimated to the area of the patient you are interested in
what is the benefit of collimation?
reduces unnecessary radiation of patient
reduces the production of scattered radiation
what is the benefit of reducing scattered radiation?
improved image quality
less exposure to staff remaining in the controlled area
how is collimation achieved?
using a light beam diaphragm
how does a light beam diaphragm work?
metal shutters alter aperture size through which primary beam will leave
how is the collimated area shown?
light directed by mirrors through the aperture
what are the key uses of the light beam diaphragm?
limiting x ray beam to necessary area
positioning of patient
what is stated by the inverse square law?
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
why is the inverse square law important in radiation safety?
the further a person is from the x ray beam the less radiation they will receive and the safer they will be
what is the effect of the inverse square law on exposure and x ray image quality?
distance between film and x ray tube should be constant so that there is a standard effect with given exposure settings
define film focal distance
distance from the x ray tube to the x ray image receptor
what must happen in FFD is altered?
mAs will need to be altered to produce a comparable radiograph
how should a new mAs be calculated if film focal distance is altered?
old mAs x (new distance squared / old distance squared)
define object film distance
distance between object being radiographed and the x ray detector
what happens to an image if the object film distance is increased?
image will be magnified
sharpness of image decreased
what can be done to keep magnification minimal?
keep patient / area of interest as close to the x ray cassette as possible
what can be done is actual sizes of structures on x rays need to be known?
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
why does increasing OFD decrease sharpness of the image?
due to an increase in size of the penumbra around the edges
how can distortion of an image be avoided?
keep the part of the patient to be imaged parallel to the x ray cassette and perpendicular to the x ray beam
what are the 3 ways in which x rays may interact with matter?
x ray photons pass through unchanged
x ray photons are absorbed
x ray photons are scattered
what is formed by x ray photons that pass through matter unchanged?
useful x-ray image
what does the proportion of x ray photons absorbed depend on?
the nature of the material they are travelling through - this concept is essential for imaging
what are the key factors which affect the absorption of x rays?
atomic number
physical density
thickness of tissues
how does atomic number affect x ray absorption?
high atomic number leads to greater absorption of x rays
how does physical density affect x ray absorption?
higher density leads to increased absorption of x rays
how does tissue thickness affect x ray absorption?
thicker tissues lead to more absorption
what does the x ray image depend on?
differential absorption of x rays by different tissues in the body
why does bone appear white on x ray?
high Z (atomic number) good absorber
why does gas appear black on x ray?
low density, poor absorber
why does soft tissue appear grey on x ray?
intermediate Z and density so intermediate absorber
what are the key issues associated with scattered x ray photons?
move in random directions lose energy not useful in image formation degrades quality of image radiation hazard
what is the purpose of x ray grids?
minimise effect of scatter on image and improve image quality by reducing the amount of scattered radiation reaching the film
when are grids useful?
when radiographing thicker areas (>10cm)
where are grids placed?
between patient and cassette
what are grids made from?
;/./flat plates consisting of a series of thin strips of lead alternating with thin radiolucent strips
what are the radiolucent strips in grids formed from?
plastic of aluminium
what is the purpose of lead strips within grids?
designed to absorb most of the scattered radiation which hits the grid in all directions
what is the purpose of radiolucent strips within a grid?
designed to allow the primary beam through (as it travels in a straight line)
why are higher exposure factors (mAs) needed if using a grid?
some scattered radiation will manage to pass through the spacing material and some of the primary beam will be absorbed by the lead
what is the grid ratio?
height of the lead strips divided by the width of the spacing material
what are typical grid ratios?
6:1 and 12:1
what type of grids are more efficient at removing scatter?
higher ratio
what is the issue with higher ratio grids?
remove more of the primary beam so a higher exposure is needed
how does lead strips per cm affect scatter and exposure?
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
what is the grid factor?
number by which the mAs must be multiplied if a grid is used
what does the grid factor depend on?
grid ratio
lines per cm
what are the types of grid?
parallel focused pseudo-focussed cross hatched moving / Potter Bucky
describe the lead strips within a parallel grid
parallel and of equal height
what effect will a parallel grid have on the primary beam?
some increase in the amount of primary beam absorbed towards the edge of the grid as the beam diverges
what are the benefits of parallel grids?
cheap and easy to use
can be used either way up and at any FFD or centering point
describe the layout of a focused grid
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
how must a focused grid be used?
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
what is a disadvantage of focused grids over parallel?
more expensive
describe pseudo-focused grids
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
what is the most efficient type of grid?
cross hatched
describe the layout of a cross hatched grid
two sets of lead strips at right angles to each other
what are the disadvantages of cross hatched grids?
require high exposures, accurate centering and are expensive
describe the layout of moving / Potter Bucky grids
parallel grids mounted permanently beneath a radiolucent x ray table top. These oscillate rapidly to and fro during exposure
what are the benefits of moving / Potter Bucky grids?
fine lines which appear on the image when a stationary grid are blurred out and not seen
does a moving / Potter Bucky grid affect image quality?
no - cassette / detector is beneath the moving grid and stays stationary so image remains sharp
historically how was the x ray image recorded?
on x ray film
how are almost all x ray images recorded now?
digital radiography
are the x ray machine and table different in digital imaging systems?
essentially unchanged
what are the 2 types of image receptor used in digital imaging?
storage phosphor cassette (CR)
flat panel detector (DR)
what is used to capture the image in computed radiography (CR)?
cassettes similar to conventional film / screen casettes
what is contained within cassettes for computed radiography?
storage phosphor plate
how is an image produced by CR digital imaging?
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
can CR phosphor plates be reused?
yes
how can CR plates be reused?
phosphor plate is erased by bright light
what should happen to CR phosphor plates if they have been unused for a period of time?
erased before use
how long does the imaging process in CR take?
around 1-2 mins
how is the CR plate read when in the cassette reader?
one line at a time
how is the image produced in direct digital systems (DR)?
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
describe the process of acquiring a digital x ray image
enter patient information (accurate and complete)
select anatomical region of interest
select animal size
why must the correct anatomical region of interest be selected during digital x ray?
processing algorithms will vary and formulae will adjust / reconstruct images based on the expected tissue types in that area
with both CR and DR systems what is shown after each exposure?
exposure index - applies numerical value to exposure (name varies between manufacturers)
what must you be aware of about your own machines exposure index?
whether it is proportional or inversely proportional to measure of exposure
how are grey scale values in digital images determined?
‘look up tables’
how do ‘look up tables’ work
input pixel intensity is mapped to an output greyscale value
what can grey scale values compensate for?
overexposure
what can be done with digital x ray images that cannot be done with conventional radiographic film?
manipulate image to show detail
how can digital images be manipulated?
filters / algorithms contrast / brightness size orientation annotation and measurement
what filters may be used on digital images?
edge enhancement
contrast enhancement
how are digital images stored?
computer files
what format are images stored in?
dicom (.dcm)
what does Dicom stand for?
digital imaging and communications in medicine
how often should images be backed up?
daily
what are the issues with printing digital images onto paper/film?
would increase cost
loss of detail
what software is used for storing images long term?
PACS - picture archiving and communication system
what is the purpose of storage software such as PACS?
facilitates identification, manipulation, backup and retrieval of images
what are the advantages of digital radiography?
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
what are the disadvantages of digital radiography?
set up costs
viewing of images is limited by computer availability
specific artifacts
ensuring adequate back up of files is essential
what is a satisfactory radiograph said to be?
diagnostic
what image quality factors can be assessed?
opacity contrast sharpness patient positioning centering of x ray beam collimation of x ray beam
what does radiographic opacity describe?
how black and white the image is overall
what does radiographic contrast describe?
differences between black, white and grey in adjacent areas
what does radiographic sharpness describe?
clarity of the image
what is radiographic opacity?
degree of blackening of the radiographu
what colour do radiopaque tissues appear?
white
what colour do radiolucent tissues appear?
black
what influences radiographic opacity?
patient (tissue type being imaged and thickness)
exposure factors
digital algorithm / processing
when will opacity of a digital image vary?
not much with differing exposures unless the image is markedly exposed
may vary with algorithm used (e.g. thorax or abdomen)
can radiographic opacity be manipulated post exposure?
yes using region of interest settings
what is radiographic contrast?
difference in radiographic opacity between adjacent areas of the image
what does a long scale of contrast show on a digital radiograph as?
many shades of grey
what does a short scale of contrast show on a digital radiograph as?
black and white (not much grey)
what does radiographic contrast depend on?
the inherent contrast of the part of the patient being radiographed
the digital algorithm being selected
the amount of scatter reaching the film
what does the inherent contrast of the part being radiographed depend on?
atomic number of tissue
density of the tissue
what does scatter produce on film?
overall blackning of film
where is more scatter generated from?
thicker areas of tissue and larger areas of collimation
how can scatter be minimised?
collimation (reduce primary beam size)
using a grid when radiographing large parts
what is radiographic sharpness?
the ability to distinguish fine detail on an image
what is radiographic sharpness decreased by?
movement (animal, table and x ray tube)
scattered radiation
object film distance
how does object film distance affect sharpness?
increase in penubra and magnification with increased object film distance
what technique faults can affect radiographs?
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
what technical radiography issue is seen in this image?
focused grid placed the wrong way up - grid cut off
what miscellaneous artefacts can be seen on radiographs?
double exposure digital exposure errors 'uberschwinger' effect ghost artefact moire artefact dirt on light guide
what happens during double exposure artefact?
2 exposures on 1 detector - not seen on DR
what artefact is shown in this image?
double exposure
what artefact is shown in this image?
digital underexposure
what artefact is shown in this image?
over exposure
when does Uberschwinger or rebound artefact occur?
when there is a large density difference between adjacent objects - excessive edge enhancement by computer algorithm
what artefact is shown in this image?
Uberschwinger or rebound artefact
when is Uberschwinger or rebound artefact commonly seen?
around orthopedic implants
what does Uberschwinger or rebound artefact look like?
implant loosening
how can Uberschwinger or rebound artefact be differentiated from implant loosening?
artefact will continue into soft tissues whereas losening will not
what causes ghost artefact?
incomplete erasure of a CR plate before use
also seen if a CR plate is exposed to light
what artefact is shown in this image?
ghost artefact
what causes Moire artefact?
arise with CR systems due to interference between the frequency of the laser reader and the number of lines per centimeter in the grid
how is Moire artefact overcome?
rotate grid by 90 degrees or chnge
how does Moire artefact appear?
bands across the image
what artefact is shown in this image?
Moire
what artefact is shown in this image?
dirt on light guide
when does dirt on light guide occur?
emitted light blocked by dirt from reaching the photomultiplier tube
how does dirt on light guide appear on a the radiograph?
line along image orientated in the direction the imaging plate moves during the reading process
how can dirt on light guide be prevented?
CR plate reader cleaning and maintenance should be performed routinely
what is the main piece of legislation governing radiography in a veterinary practice?
ionising radiation regulations 2017
what are the 3 basic principles of safe x rays?
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
what is the key effect of ionising radiation?
damages living tissue (cells)
what are the 3 key effects of ionising radiation?
carcinogenic
somatic
genetic / mutation
what are the carcinogenic effects of ionising radiation?
tumor development in cells that have been exposed to radiation
what are the somatic effects of ionising radiation?
direct changes in body tissues that occur not long after exposure has occurred (e.g. radiotherapy effects)
what are the genetic / mutation effects of ionising radiation?
occur when gonads are irradiated and mutations occur in the chromosomes, May give rise to abnormalities in offspring
what are the main sources of radiation hazard?
tube head
primary beam
scatter
what happens to the intensity of scatter as it moves away from the source?
reduces in intensity
how can scattered radiation be reduced?
tight collimation reduced exposure factors (as much as possible) PPE used lead cover on table rotation of staff
what are the general requirements if a practice intends to use x rays?
HSE must be notified
practice must appoint radiation protection supervisor (RPS)
radiation protection advisor (RPA) will be appointed
who draws up the local rules and system of work relating to ionising radiation safety?
RPA
what do local rules around ionising radiation ensure?
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
what is the ionising radiation system of work prepared by?
RPA and RPS
where should the ionising radiation systems of work be displayed?
whenre everyone can access and read them
what information is included in the system of work?
SOP for x rays
RPS details
description of restricted areas
what todo in the event of an accident
where is the controlled area defined as?
area where radiation dose will exceed 7.5 mSv/h
where is the controlled area usually located?
specific room
how large should the controlled area be?
large enough for 2 people to be 2m away from primary beam (or able to exit room)
how can the controlled area be identified?
warning signs
what can indicate that an exposure is being taken?
light
use of voice
beep
how are personnel protected?
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
what considerations must be made to ensure PPE is functional?
hung up properly (no folding)
should be regularly x rayed to chack integrity
what are dose limits set to do?
protect workers and members of the public from the effects of ionising radiation
what level are dose limits set at?
one which balance the risk from exposure with the benefits of ionising radiation
what are the different classes of people who have different dose limits?
adult employees aged 18 or over
trainees aged 16 to 18
any other person, such as a member of the public
what enables detection of radiation to take place?
dosimeters must be worn by staff
what are the 2 types of dosimeters?
film badges
thermoluminescent detectors
how do film badges detect radiation dose?
contain a small piece of film processed photographically. Film blackening is proportional to exposure
how do thermoluminescent detectors detect radiation exposure?
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
how long are dosimeter worn for?
4, 8 or 12 weeks
where are dosimeters returned to to be read and reported on?
national radiation protection board
can dosimeter badges be shared?
no - everyone must have their own
where must badges only be worn?
at work, at waist level under lead apron
what must dosimeters be protected from?
water
excessive heat
physical damage
who should read the dosimeter report from the NRPB?
RPS or practice manager
how long must dosimeter records be kept for?
2 years
what are contrast media?
agents that are more or less opaque than surrounding tissue
what do contrast media do?
delineate organs / cavities within the body
what is the purpose of contrast media?
to see structures not normally visible or poorly visible
to gain more information about soft tissue structures
what are the 2 key types of contrast media?
positive contrast
negative contrast
what colour does positive contrast appear as on radiographs?
white
why does positive contrast appear white on radiographs?
due to its high atomic number - absorbs x ray beam
give 2 examples of positive contrast media
barium
iodine
what is used for negative contrast?
a gas (air or CO2)
what colour does negative contrast show up as on x ray?
black
why does negative contrast media show as black on x ray?
low density - doesn’t stop x rays
what area of the body is barium used to study?
GI tract
in what formulations may barium be supplied?
powder
suspension
why is barium a good contrast medium?
inert non - toxic reasonably palatable cheap good mucosal detail no osmotic effect
why is it important that barium has a low osmotic effect?
so that it is not diluted during it’s movement through the GI tract
aside from barium what is used as positive contrast?
water soluble iodine-containing preparations
what are the 2 main groups of iodine contrast media?
ionic
non-ionic
how is iodine introduced into the body for a contrast study?
IV
how is iodine eliminated from the body after a contrast study?
renal excretion
what are 2 examples of ionic iodine contrast?
urografin 150
conray 420
what are 2 examples of non-ionic iodine contrast?
omnipaque 300
Niopam
what does the number following the name of the iodine contrast relate to?
how many mg of iodine there are per ml of solution
what are the disadvantages of ionic water-soluble iodinated contrast media?
irritant extravascularly toxic in large doses viscous contraindicated IV in patients with cardiovascular or renal insufficiency contraindicated for mylography
how can the viscosity of ionic water-soluble iodinated contrast media be reduced?
warming before use
why is ionic water-soluble iodinated contrast media contraindicated for myelography?
involves interaction with subarachnoid space
what studies can non-ionic water-soluble iodinated contrast media be used for?
all
what are the disadvantages of non-ionic water-soluble iodinated contrast media?
slightly more expensive
viscous
side effects can still occur although are rare
what are the side effects associated with water-soluble iodinated contrast media?
anaphylaxis nephrotoxicity urticaria vomiting pyrexia
what are the advantages of negative contrast media?
cheap (free!)
simple to use
relatively safe
can combine with positive contrast agents for double contrast studies
what are the disadvantages of negative contrast media?
very small risk of air embolism
poor mucosal detail
produce less contrast than positive contrast agents
how can the risk of air embolism when using negative contrast studies be reduced?
perform study in left lateral recumbancy rather than right
what must be considered before contrast radiography is used?
indications - will lesion be shown time involved cost correct preparation of patient (enema / feeding) restraint needed
what type of radiograph must be taken before contrast is used?
plain
why must plain radiographs be taken before contrast is used?
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
what is the safest way of dosing contrast for cystography?
palapation of bladder during study to see how filled it is becoming
what has replaced many contrast GI studies?
endoscopy
what is often used to diagnose PSS or for urinary tract investigations?
ultrasound
what studies have replaced myelography?
CT and MRI (although CT still uses contrast in some cases)
what are the indications for barium swallow?
dysphagia
regurgitation
suspected rupture
what anatomy is shown by a barium swallow?
pharynx and oesophagus
what forms of barium can be administered for a barium swallow?
liquid barium and/or barium food
what type of contrast should be used if oesophageal rupture is suspected?
iodinated contrast
when must care be taken when administering barium?
if there is swallowing issues, respiratory distress or animal is weak - aspiration risk
what does a barium ‘follow through’ study evaluate?
stomach and small intestine
in what form is barium given in a ‘follow through’ study?
liquid via mouth or stomach tube
when are radiographs taken during a barium ‘follow through’ study?
immediately then at intervals depending on transit time until barium is in colon / 24 hours reached
what techniques have largely superseded barium ‘follow through’ studies?
ultrasound and endoscopy
what is evaluated by a barium enema?
large intestine
how is barium introduced into the large intestine?
liquid barium infused into rectum post-enema
can be followed with air for double contrast
what are the main issues with barium enema?
messy and difficult to interpret
when may a small volume of contrast in the colon be useful?
to identify colon if unclear on radiograph
what other techniques can be used in place of barium enema?
endoscopy
assessment of colonic wall by ultrasound
what are the main complications of a barium enema?
leakage
overinflation with air leading to rupture
both rare
what contrast studies are used in the urinary tract?
IV urography
cystography
urethrography
what contrast medium must be used in the urinary tract?
water-soluble iodinated contrast media NEVER barium
why can’t barium be used in studies of the urinary tract?
cannot be given IV as no suspension
irritant in bladder that can lead to granulomatous cystitis
what is excretory urography used for?
identify and assess kidneys
assess ureters
assess vesicoureteral junction
where is contrast given during excretory urography?
bolus of contrast into peripheral vein
when are radiographs taken during excretory radiography?
immediately
5 mins
10 mins
15 mins
what type of radiograph is taken immediately after injection of contrast for excretory urography?
nephrogram - VD
what type of radiograph is taken 5 mins after injection of contrast for excretory urography?
pyelogram (renal pelvis) - VD
what type of radiograph is taken 10 mins after injection of contrast for excretory urography?
ureterogram - lateral
what type of radiograph is taken 15 mins after injection of contrast for excretory urography?
ureterovesicular junction - lateral
what is shown during cystography?
delineates bladder
how is contrast introduced during cystography?
urinary catheter
what happens during pneumocystogram?
air introduced into the bladder only
what is shown during pneumocystogram?
bladder location
large masses
marked thickening
what contrast is used during a positive contrast cystogram?
iodinated contrast
what does a positive contrast cystogram show?
leakage and location
what contrast is used during double contrast cystogram?
both agents - positive and negative
what is shown during double contrast cystograms?
delineation of wall and content of bladder
what is shown in a vagino-urethrography?
urethra and vagina
what contrast medium is used during vagino-urethrography?
water soluble iodinated contrast medium
how is contrast media introduced into the urethra / vestibule during vaginourethrography?
via foley catheter
what is a possible complication arising from vaginourethrography?
urethral damage due to over distention and damage from catheter
what is shown during myelography?
delineates subarachnoid space and localises lesions of the spinal cord
what contrast medium must be used for myelography?
non-ionic water soluable contrast media
why must non-ionic water soluable contrast media be used in myelography?
ionic can cause seizures / arachnoiditis
what has largely replaced myelography?
CT and MRI
CT myelography is still performed
how must the patients head be kept during recovery from myelography?
elevated
why must the patients head be kept elevated during recovery from myelography?
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
what must be available at all times during myelography?
patent IV catheter
IV diazepam
what is shown during angiography?
blood vessels
what is shown during arthrography?
joints
what is shown during fistulography?
sinus tracts
what must happen if any positive contrast media is spilled?
it is wiped up otherwise artefacts will appear on the developed radiograph
what checks must be made before taking an exposure?
correct animal
decide on projections needed
select exposure facts / grid
ensure animal is placed over cassette or grid
appropriate centering and and collimation
what is positioning?
the use of pads, wedges, sandbags and ties to ensure that the animal is straight and restrained for the examinatio
what is centring?
using the light beam diaphragm, the primary beam is positioned directly over the correct surface landmark for the examination
what are the only x rays that should be taken?
only films that are clinically indicatd
under what circumstances may an individual be able to remain in the room during an exposure?
holding cassettes for equine imaging
inflating chest
injecting contrast
what should be worn if someone is within the room during x ray exposure?
lead PPE
what is the role of lead protection?
protects against scattered radiation
what must be considered when using a horizontal beam?
the walls and what is beyond the room as radiation doesn’t stop at x ray cassette
what can be done to enure x rays don’t pass through the wall when a horizontal beam is used?
double brick equivilent
lead screen
barium plaster
how can an animal be restrained for imaging?
GA
sedation
positioning aids
why is patient restraint essential?
to prevent low quality or non diagnostic images
what is the role of positioning aids?
maintain appropriate position for capture of radiograph
what positioning aids are useful for VD/DV exposures?
troughs
what can troughs be formed from?
radiolucent foam or plastic
what can be used to support different areas of anatomy?
foam pads and wedges
what must happen to foam pads and wedges if they come into contact with contrast medium?
washed
why must care be taken when using sandbags to position a patient for x ray?
sand is radiopaque so will be seen on the image if in the collimated area
what can be used to tie legs?
tapes
rope ties
what additional equipment may be used when imaging horses?
positioning blocks
cassette holders
rope head collar for imaging of head
what must you be aware of on cats and dogs that can interfere with x ray image?
collars and harnesses
when should ties only be used?
when an animal is under GA so won’t wake up
when is care needed with positioning?
injured or debilitated patients
what should be avoided while x raying?
loud noises or sudden movements
what are markers used for during x rays?
identifying included area of anatomy, limb, side or recumbancy of the patient
what is the minimum information that should be put on an x ray film?
animals name
owner surname
date
when should identification be on film?
before processing or saving image
how is patient identification placed on an image within a digital system?
entered first before any images taken
how is patient identification placed on an image in conventional film?
x-rite tape
actinic (light marker)
what should you check when assessing the radiograph?
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
what are the critical decisions to be made when assessing the radiograph?
any repeats needed
any further views needed
when naming projections what is described?
path of the x ray beam from the x ray tube to the image receptor
what will also be provided by projection name?
information about the position of the animal (e.g. ventrodorsal - on their back)
what are lateral projections named after?
the side the animal is lying on
how can image magnification be minimised?
body close to cassette
why does the body need to be parallel to the cassette?
minimise distortion
