Radiology Flashcards
What important legislation is in place regarding Ionising radiation?
- ionising radiation regulations 2017
- ionising radiation (medical exposure) regulations 2017
What is a radiograph?
An image produced by x-rays passing through an object and interacting with photographic emulsion on a film.
What is used to capture a digital x-ray image?
A solid state sensor or Photo-stimulable phosphor plate
In dentistry, what tissues are of interest in regards to radiographs?
Mineralised and demineralised tissue
What would demineralised tissue on a dental radiograph indicate?
Caries and other dentally related disease
What type of radiograph matches the description:
- Film/ sensor is placed inside the mouth next to the area of interest
- Radiation source is directed at the areas from an external position
Intra-oral radiograph
What are the three main types of intra-oral radiograph?
- periapical
- bitewing
- occlusal
What type of radiograph matches the description:
- Nothing placed inside the mouth
- Radiation source and image receptor are both positioned outwith the mouth
Extra-oral radiograph
What can DPT also be referred to as?
OPT and OPG
What is contained within the nucleus of an atom?
Protons and neutrons
Are protons +ve, -ve or no charge?
+ve charge
Are neutrons +ve, -ve or no charge?
No charge
Are electrons +ve, -ve or no charge?
-ve charge
How many electrons are in the K shell (closest to nucleus)?
2
How many electrons are in the L shell of an atom?
8
What can move from shell to shell but cannot exist between shells?
Electrons
Which electrons in an atom will have the greatest binding energy?
Outer electrons
What is an atom with the same number of protons but a different number of neutrons referred to as?
An isotope
Describe a radio-isotope
An isotope with unstable nuclei which undergoes radioactive disintegration
What is a negatively charged ion called?
An anion
What is a positively charged ion called?
A cation
What type of particles have these features?:
Made up of 2 protons and 2 neutrons
- large size
- +ve charge
- slow speed
- penetrate only 1-2mm in tissue
- 4-8 MeV energy
- extensive ionisation
Alpha particles
What type of particles have these features?:
- Electrons
- small size
- -ve charge
- fast speed
- penetrate 1-2cm in tissue
- 100keV-6MeV energy
- ionisation
Beta particles
What type of rays is part of the electromagnetic radiation spectrum, has no size or charge and has very fast speed , passing through tissues?
Gamma rays
What type of rays are x-rays in dentistry almost identical to? And what is the slight difference?
Gamma rays, except x-rays have lower energy values
When is ionisation a problem?
When it occurs in living cells, can cause damage to DNA leading to tumours and cancer.
What size of wavelength do gamma rays have?
Small wavelength
Define the electromagnetic spectrum
A stream of photons that have no mass
What is measured in electron volts (eV)?
Energy
What is measured in cycles per second or hertz?
Frequency
What is measured in metres or nanometres?
Wavelength
One cycle of a wave length is what shape?
S-shaped
What is the number of wavelengths that travel every second the same as?
Frequency
What is the wavelength spectrum for visible light?
400-700nm
What is the domestic electricity supply?
220/240 volts
50 hertz
What is the SI unit of potential difference? And what does it measure?
Volts
It measures voltage or electromotive force
Describe an electrical circuit using a dc supply
A current passes along a wire by the movement of electrons and through an electrolyte by the movement of ions, from the positive terminal to the negative terminal.
In the example of an old-fashioned electric fire, how is heat given off?
By means of convection and radiation
How do electrons produce heat?
By vibrating
What are the three basic components involved in taking a radiograph?
- X-ray source
- Object
- Receptor
What is key to the quality of an image?
The relationship of X-ray source, object and receptor to one another
What are three types of intra-oral radiograph?
- periapical
- bitewing ( horizontal and vertical)
- occlusal (maxilla and mandible)
When taking an intra-oral radiograph, where would the receptor be placed?
Inside the mouth
When taking an extra-oral radiograph, where would the receptor be placed?
Alongside the patient
What are five types of extra-oral radiographs?
- dental panoramic tomogram
- lateral cephalogram
- PA or AP mandible
- lateral oblique mandible
- Occipital-mental views of facial bones
On a peri-apical radiograph, what should be visible?
The crown to the apices of the root, and inter-proximal spaces
What are the limitations of a horizontal bitewing?
You are not able to visualise the roots
What radiograph would you consider taking if you wanted to assess bone levels of posterior teeth?
Bitewing, either horizontal or vertical
What type of extra-oral radiograph is described:
The x-ray tube rotates round the patients head with a constant long exposure of 14 seconds, forming an image of the patient’s teeth and supporting structures
DPT
What type of extra-oral radiograph is described:
A standardised and reproducible form of skull radiography, used extensively in orthodontics to asses the relationships of the teeth to the jaws and the mandible to the rest of facial skeleton
Lateral cephalogram
What type of extra-oral radiograph is described:
Shows fractures of the mandible and is used in conjunction with a DPT. it requires two views taken at right angles to one another to show full extent of fracture.
Posterior-anterior mandible
It is common for there to be multiple fractures in the mandible. True or false?
True
What type of extra-oral radiograph is described:
Most commonly carried out in a dental hospital in children that cannot tolerate bitewings. Also carried out on adults for, mandibular fractures if a DPT is not available.
Lateral oblique mandible
What type of extra-oral radiograph is described:
Most commonly carried out in the first instance when patient reports with facial trauma. Shows fractures of the orbit, maxilla and zygomatic arches. Two views are taken, the first angle at 10 degrees and the second angle at 30 degrees.
Occipito-mental views of facial bone
When taking an occipital mental view of the facial bones, why is it beneficial to take the films erect?
As this can help demonstrates fluid levels in antra (sinus)
Why are intra-oral radiographs in more detail that extra-oral?
Because the object is closer to the receptor
What selection criteria helps decide the most appropriate form of imaging required when deciding what radiograph to take?
FGDP selection criteria for dental radiography
What are the two main types of technique used for intra-oral radiographs?
- paralleling technique
- bisected angle technique
What is the standardised intra-oral technique?
Paralleling technique
When would you opt for the bisected angle technique over the paralleling technique?
When a patient cannot tolerate a holder in their mouth
What is the main issue surrounding bisected angle technique?
Exposure of patients fingers to radiation as they are required to hold film in mouth
What is the downside of the paralleling technique?
Holders are bulky and may not be tolerated by patient.
What part of the mouth are blue holders used to visualise?
Anterior teeth
What part of the mouth are yellow holders used to visualise?
Posterior teeth
What colour of holder is used for bitewings?
Red holder
What colour of holder is used for endodontic procedures?
Green holder
What are the three components of holders?
- Bite-block
- Indicator arm/rod
- Aiming ring
What is the function of a bite-block?
Retains the receptor
What is the function of the indicator arm/rod?
Fits into the bite-block
What is the function of the aiming ring?
Slides onto the arm to establish alignment of collimator with receptor, guiding direction of the x-ray beam
What is a receptor?
The object an image is taken on
what type of receptors are used in dundee dental hospital?
Phosphor plates
What reduces the variables in geometry?
Use of a holder
What are examples of variables in geometry?
- Receptor-tooth relationship
- X-ray tube position
How should the vertical plane of the film be positioned?
So that it is parallel to the long axis of the tooth
How should the horizontal plane of the film be positioned?
Parallel to the central arch under examination
If the film isn’t parallel with the tooth vertically, what may happen?
Distortion of the image (teeth elongated and apices missing)
If horizontal positioning of the film is incorrect what may happen?
Teeth appear overlapped, obscuring pathology
What angle should the x-ray beam be to the tooth/receptor?
90 degrees ( right angle )
If the angle of the x-ray beam is up too much, how will the image be distorted?
Elongation of image
If the angle of the x-ray beam is down too much, how will the image be distorted?
Fore-shortening of image
What is the rectangular attachment at the end of the x-ray tube known as?
Collimater
what will help achieve the most diagnostic, reproducible image?
Having the 4 corners of the collimator fitting nicely into the aiming ring
What two factors affect image size?
- X-ray source to receptor distance
- Object to receptor distance
Explain how the object comes to appear larger on the receptor
X-ray beam spreads out in all directions from the source and it continues to spread as it passes through the object, thus making it appear larger.
What action should be taken in regards to the x-ray source in order to get a more accurate depiction of the image?
X-ray source should be positioned further away from the object (beam diverges less)
What should the distance between source and film be?
Long
What should distance between tooth and film be?
Short
What is ‘cone cutting’ a result of?
Vertical angulation, when corners of the collimator have not been touching the guiding ring.
What are the four main barriers to good positioning?
-mouth size
-gag reflex
-film size
-digital sensor size and shape
What are the 4 most common sizes of film/ PSP receptors?
0, 1, 2, 4
What should the film size be for:
Periapical radiograph of anterior adult teeth
0 or 1
What should the film size be for:
Periapical radiograph of anterior adult teeth using bisected angle technique
2
What should the film size be for:
Periapical radiograph of posterior adult teeth
2
What should the film size be for:
Bitewing radiograph of adult teeth
2
What should the film size be for:
Periapical radiograph of anterior children’s teeth
0
What should the film size be for:
Periapical radiograph of posterior children’s teeth (deciduous and permanent)
Deciduous = 0
Permanent = 2
What should the film size be for:
Bitewing radiograph of children over 10
2
What should the film size be for:
Bitewing radiograph of children under 10
0 or 1
what is the “controlled area”?
The area in the immediate vicinity around the x-ray source
What material is the cathode made from? And why?
Tungsten, because it has a very high melting point so can withstand the production of heat from x-rays
What materials make up the anode?
Tungsten and copper
What are the two types of x-ray spectra?
- Continuous spectrum
- Characteristic spectrum
What x-ray spectra is bremsstrahlung radiation associated with?
Continuous spectrum
What is the negatively charged electron from the cathode attracted to?
The positively charged atom of tungsten within the anode
What type of deflections are most common and associated with low energy photons?
Small deflections
What type of deflections are less Likely and associated with high energy photons?
Large deflections
What is maximum photon energy directly related to?
KV across the x-ray tube
What is termed the “ejected orbital electron”?
An incident electron that knocks a k shell electron out
What is line spectra relating to K and L shells associated with?
Characteristic spectrum
Spectra relating to which atomic shell is of diagnostic importance?
K shell
What kV value must x-rays be operating above in order for the characteristic spectrum to be produced?
Above 69.5kV
If x-ray tube operates below 69.5kV, what radiation will be produced?
Bremsstrahlung radiation
What two divisions make up the electromagnetic spectrum?
Non-ionising and ionising radiation
If the wavelength is large, what division of EM spectrum radiation is most likely associated?
Non-ionising radiation
If the wavelength is small, what division of EM spectrum radiation is most likely associated?
Ionising radiation
Random change in direction after hitting something
Scattering
Deposition of energy in tissues
Absorption
The number of x-ray photons in a defined area of the beam
Intensity
What happens to the energy of x-ray photons the further from the source of radiation you go?
Energy decreases
Reduction in intensity of beam, due to scattering and absorption
Attenuation
Removal of electron from neutral atom to give -ve (electron) & +ve (atom) ions
Ionisation
The ability of photons to pass through or into tissues/materials
Penetration
What are the four types of x-ray interactions that can occur when x-ray photons hit an object?
- Completely scattered with no loss of energy
- Absorbed with total loss of energy
- Scattered with some absorption & loss of energy
- Transmitted unchanged
What is internal scatter?
When some of the radiation passes down into patients body
How would you describe scatter of x-ray photons?
Unpredictable
Define radiation dose
The amount of radiation absorbed by the patient
Where are low energy photons often absorbed?
Soft tissues
What type of photon energy is most likely to cause biological damage?
Low energy photons absorbed by soft tissues
What do properties of radiation depend on?
Wavelength
The item the x-ray image is formed on
Image receptor
Give three examples of image receptors
Film, plate or digital sensor
What is meant by ‘ fogging of the film’?
When some photons do not have enough energy to make a useful interaction with the receptor, therefore resultant scatter of photons can degrade the image.
What are the two ways to capture an x-ray image?
Film or digital
What are the two types of film image receptors that can be used?
- direct action film
- indirect action film
What are the two types of digital image receptors?
-solid state sensor
- photo-stimulate phosphor (PSP)
What image receptor is described:
- An actual piece of film which is sensitive to x-rays that is wrapped in a packet.
- used intra-orally, x-ray directly acts on silver halide crystals in film emulsion
Direct film
What image receptor is described:
- a film inside a cassette which contains intensifying screens, that x-ray photons interact with to produce light photons, exposing the film to produce the image.
- used extra-orally, light from intensifying screens act on silver halide crystals in film emulsion
Indirect film
What image receptor is described:
Two types of sensors:
- CCD and CMOS
These work by converting light into electrons
Solid state sensor
What does CCD stand for?
Charge-coupled device
What does CMOS stand for?
Complimentary metal-oxide semiconductor
What image receptor is described:
Latent image produced by the interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce an image.
Phosphor- stimulable phosphor (PSP)
which digital sensor can sometimes not be tolerated well by patients, due to it’s large and bulky nature?
Solid state sensors
Which digital sensor has better image resolution?
Solid state sensors
What are the two sides of a phosphor plate?
- Phosphor coating side ( white)
- Black side with orientation dot
which side of a phosphor plate is the image formed on?
Phosphor coating side ( white)
what side of the phosphor plate should be visible through the window of a protective bag?
The black side
Describe the stable excited state
Image plate placed in patients mouth and phosphor coating is exposed to x-rays which causes a reaction within the phosphor.
Describe the unstable excited state
The plate is dropped into the vista scan unit where it is scanned by a red laser
What type of light is emitted to be differed into an image once the phosphor plate is scanned by red laser?
Blue light
What are the 4 layers that make up a charge couple device? And what is their function?
- front cover
- scintillator layer (converts x-ray energy to light)
- silicon layer ( converts light into electrical signal)
- back cover ( incorporates a cable to carry signal to pc)
What is the difference between CCD and CMOS?
CMOS - signals sent from each individual cell (pixel)
CDD- signals sent from lines of cells (pixels)
What is the issue with digital images?
There is no orientation dot visible on the image. This means you may have images that could be very easy to turn the wrong way and get muddled up.
What type of solid state sensor has higher quality image production?
CCD
Name 6 reasons why digital image receptors would be chosen over film?
- No chemicals
- Faster processing times
- Easy archiving
- Easy image transfer
- Image manipulation
- Dose reduction
In regards to the resolution of an image, what happens in response to shorter exposure of image?
A drop in image resolution
What size would a pixel be to make an image less detailed?
Large
What happens to exposure if there is too much radiation?
High exposure and image appears dark
What happens to exposure if there is no enough radiation?
Low exposure and the image appears pale
What does PACS stand for?
Picture archiving and communication system
What are the different sizes of receptor for digital PSP’s?
0,1,2 and 4
What is the one available size of solid state receptor?
2
Why might using a size 2 solid state receptor make x-raying anterior teeth difficult?
Due to large size of receptor and subsequent positioning in the mouth
What are the two types of biological effects of radiation?
Deterministic and non deterministic
Those biological effects that WILL occur are known as?
Deterministic effects
Those biological effects that we know MAY occur are known as?
Non deterministic
Which type of biological effect of radiation has a threshold dose? Deterministic or non-deterministic
Deterministic
Define somatic effects
Those suffered by the exposed person
What type of deterministic effect can be more aggressive and traumatic, acute or chronic?
Acute
What biological effects of radiation occur at random, due to chance or probability?
Non deterministic effects
Which type of effects are we likely to have in dentistry?
Non deterministic
What are the three main factors affecting dose of radiation?
- Type of radiation
- Tissues being irradiated
- Age of the patient
What is the typical effective dose of radiation for bitewings/periapicals?
0.0003-0.022 mSv
What is the dose limit for the public? Value that should not be exceeded
1 mSv
What is the principle used to manage safe dose limits for dental patients?
ALARP
What does ALARP stand for?
As
Low
As
Reasonably
Practicable
What film speed will reduce the risk of developing fatal malignancy?
F speed ( very fast)
The number of “photons” in a beam at a specific place represents…
Intensity of x-ray beam
What is the intensity of radiation proportional to?
1/ distance (squared)
What does the size of the controlled area depend on?
KV of the x-ray machine
If x-ray machine produces 70kV, what will the size of the controlled area be?
1.5m
What does the plastic barrier wrapped around film do?
Protects film from saliva and is good for infection control
How many layers are there in a direct action film packet?
4
What are the 4 layers in a direct action film packet?
- Outer plastic wrapping
- Black paper
- Lead foil
- Film
Which layer of direct action film:
Keeps film dry, protects it from fogging and indicates the correct orientation of the film inside the mouth?
Outer plastic wrapping
Why can you only open film packet in a dark room under a safe light?
Because radiographic film is photosensitive, which means it will react with light
Which layer of direct action film:
Protects films for light leakage and stiffens/ supports the film to prevent crimp/pressure marks appearing?
Black paper
Which layer of direct action film:
Is composed of a mixture of lead and aluminium, readily absorbs x-rays, prevents back scatter and has a distinct pattern embossed into lead?
Lead foil
Which layer of direct action film:
Is composed of: base layer, adhesive layer (with anti-glare tint), followed by double emulsion layers and gelatin protective layer?
Film
What layer of film reacts with x-rays to form an image?
Emulsion layer
What components make up the emulsion layer of film?
Silver halide crystals suspended in gelatin
What are the two functions of gelatin?
- allows even distribution of crystals
- absorbs liquid readily to allow processing
what is the function of the adhesive layer of film?
Sticks the emulsion to the base layer
How is a direct action “latent image” formed?
X-ray photons hit silver halide crystal emulsion of film. Silver halide crystal becomes sensitised, this is known as the LATENT IMAGE.
The pattern produced within the emulsion by the sensitising of silver bromide/iodide crystals, either by light or x-rays.
Latent image
What is the main reaction involved in creating a latent image?
The reduction of the silver bromide crystals to black metallic silver
What are the two available speeds of film?
Slow and fast
What other term can be used for ‘speed of film’?
Sensitivity of film to x-rays ( the exposure required to produce a given amount of blackening on an image)
What is the effect on film speed, the larger the crystal?
The faster the film speed
What is the sensitivity of the film dependant upon?
The size of crystals in the emulsion
If the film speed is fast, is the amount of x-rays required to produce an image higher or lower?
Lower
How does indirect film differ from direct film?
It is sensitive to light rather than x-rays
What are the four layers that comprise intensifying screens?
- base layer
- reflective layer
- phosphor layer
- supercoat
What material makes up the base layer of intensifying screens?
Polyester
what is the purpose of the reflective layer of intensifying screens?
Reflects light produced back towards film
What is the function of the phosphor layer in an intensifying screen?
Contains fluorescent phosphors which emit light when excited by X-rays
What is the purpose of the super coat layer of intensifying screens?
Protects phosphor layer from damage
What do intensifying screens allow for?
A reduction in exposure and therefore a reduced dose to patient
The reduction of the exposed silver bromide crystal to black metallic silver and then making the image permanent is known as?
Film processing
what are the three methods of film processing?
- Automatic
- Manual
- Instant
Which type of film processing only tends to be done in emergency situations as it is unreliable?
Instant film processing
What are the five stages of film processing?
- Develop
- Wash
- Fix
- Wash
- Dry
What occurs in the develop stage of film processing?
Makes latent image visible
What occurs in the two wash stages of film processing?
- ( after develop stage) Stops development by removing excess developer from film
- (after fix stage) Stops fix and removes residual fixer
What happens in the fix stage of film processing?
Makes image permanent
What happens in the dry stage of film processing?
Makes film easier to handle and prevents damage
What are the two developing agents that act upon silver halide crystals, sensitising them by chemical reduction of silver bromide to silver + bromide?
Phenidone and hydroquinone
What is the activator within the developer that controls the activity of developing agents?
Calcium carbonate
What is restrained within the developer that stops the developer working on unexposed crystals?
Potassium bromide
What is the preservative within the developer that slows down oxidation?
Sodium sulphite
What is the solvent within the developer that dilutes the chemicals?
Water
What is very important to note about working temperatures of developers?
Each developer has its optimum working temperature
What are the three factors that the action of developing agent on silver halide crystals depends on?
- Time
- Temperature
- Concentration
If the film stays in developer too long, how will it appear?
Dark
If the film stays in developer too short, how will it appear?
Light
If the film is too hot, how will it appear?
Dark
If the film is too cold, how will it appear?
Light
If the film is too concentrated, how will it appear?
Dark
If the film isn’t concentrated enough, how will it appear?
Light
how will silver halide crystals which are developed but not fixed appear?
Black
What is the role of fixing agents?
Change unexposed silver halide to soluble compound so they can be washed away
What maintains the pH and neutralises the developer?
Acid
What are the 5 components of fixer stage of film processing?
- Clearing agent (ammonium thiosulphate)
- Acidifier (acetic acid)
- Hardener (aluminium chloride)
- Preservative (sodium sulphite)
- Solvent (water)
What happens to unexposed silver halide crystals during fixing?
They are removed
How will under-fixed images appear?
They will have a green tinge and will not archive well
What is the difference between a manual wash and an automatic wash of the film?
Manual wash occurs between develop stage and fix stage and then between fix stage and dry stage. Whereas, automatic wash only occurs between fix stage and dry stage.
What is the purpose of washing the film?
Removes unexposed silver halide crystal once made soluble by fixer
What will the effect of insufficient washing do to the film?
Make film feel sticky and look cloudy
Which method of film processing is the best?
Automatic film processing
When would instant film processing be beneficial?
If you have to process images away from a power source
What is the main regulation used for health and safety when carrying out radiographs?
COSHH
What does COSHH stand for?
Control of substances hazardous to health
What work act meant that employers has a legal duty to ensure their staffs were safe and risk free at work?
HEALTH AND SAFETY AT WORK ACT 1974
What must manufactures supply for potential hazardous substances that makes you aware of how dangerous your developer and fixer are?
Material safety data sheets
What are the key four reasons to take bitewing radiographs?
- To detect caries
- To monitor caries progression
- To assess periodontal status
- To assess existing restorations
What happens in a caries risk assessment?
You perform images at regular intervals
What are the advantages of horizontal bitewing over vertical?
Usually only two images taken whereas verticals require 4 images to be taken
What is the advantage of vertical bitewings?
They demonstrate more of the roots
In a horizontal bitewing, where should the centre of the bite block be placed so to cover the whole region of interest?
On the centre of the 6
When would you pick a vertical bitewing over a horizontal bitewing?
When you need to see more of the root and supporting bone
What are the positioning requirements for bitewings?
- Film and object parallel
- Film close to object
- X-ray beam perpendicular to object and film
How do we achieve good positioning?
By always using a holder
what could be used as an alternative to film holder if patient cannot tolerate it?
Paper tab
What does use of a guiding ring ensure?
That the x-ray beam is certain to hit the centre of the receptor
When may horizontal overlap of teeth be difficult to avoid?
If there is crowding or tilting of teeth
When would horizontal overlap of teeth be deemed acceptable?
If less than half of enamel is superimposed
What are the two problems associated with vertical angulation of x-ray beam to receptor?
- Upper bone levels will be projected off the receptor
- Resultant distortion of the teeth has caused separation of the cusps
On a bitewing, where does the ‘dot’ on the receptor go?
Always to the palate
If a child refuses to cooperate with bitewings what is the alternative?
Lateral oblique mandible images
what can reduce the dose of radiation to patients by up to 50%?
Use of rectangular collimation
Why is legislation for radiology necessary?
Helps to minimise risks from radiation exposure
What regulations concern equipment and the protection of staff and the general public?
IRR17
What regulations are aimed primarily at the protection of patients?
IR(ME)R 17
What was the necessary regulations in place before the updated IRR17?
IRR99
When would you consult your radiation protection advisor (RPA)?
If planning set up of a new surgery, or when radiation is over dose
What does IR(ME)R stand for?
Ionising radiation ( medical exposures) regulations
What are the four roles in radiography?
- Employer
- Referrer
- Practitioner
- Operator
Who entitles staff in various roles to undertake roles involved in IR(ME)R?
Employers
What is the selection of a radiograph based upon?
Patients history and examination
What is choice of radiograph based on?
The prevalence of the disease, rate of progression and diagnostic accuracy of imaging technique
What is the purpose of selection criteria?
Helps to overcome the wide variation in practice and minimise or prevent any inappropriate radiographic examinations
Who is ‘the referrer’?
A registered dental practitioner who is entitled in accordance with the employers procedures to refer individuals for medical exposure to a practitioner
Which member of the dental team has limited entitlement as an “operator”?
Dental nurse
Who can take radiographs in general dental practice?
- a dentist
- a dental hygienist or therapist
- a suitably qualified dental nurse
- a clinical dental technician
what does the “operator” do?
Takes radiographs
Clinical evaluation of each exposure must take place. What is clinical evaluation?
Interpretation of the outcome and implications of, and the information resulting from, a medical exposure
What is the relationship between the practitioner and the operator?
Shall co-operate, regarding practical aspects, with other specialists and staff involved in a medical exposure, as appropriate
How often should x-ray units be tested?
Preferably annually but minimum of every 3 years
What are the optimum viewing condition for diagnosing caries using a radiograph?
Low ambient light and a bright screen limited to area of image
Why do we get ‘cervical burnout’?
The x-ray photons over-penetrate or burn out the thinner tooth edge and create the radiolucent area that mimics cervical caries
How often should a high risk child receive an intra-oral radiograph?
6 monthly
How often should a moderate risk child receive an intra-oral radiograph?
Annually
How often should a low risk child receive an intra-oral radiograph?
12-18 months (deciduous teeth)
24 months or more (permanent teeth)
The supportive and connective tissue element which form in cancellous bone
Trabecula
What is the trabecula pattern?
Course of stress lines along the bone and maximum trabeculae develop along the lines of maximum stress
what type of trabecula pattern does the mandible have?
Thick, close together, horizontally aligned
what type of trabecula pattern does the maxilla have?
Finer, more widely spaced, no obvious alignment pattern
The three most important features to look at when assessing if there is peri-radicular disease on a radiograph, are?
- radiolucent line representing the periodontal ligament space
- radioopaque line representing lamina dura
- trabecula pattern and density of surrounding bone
What is the radiographic appearance of initial acute inflammation in periapical pathology?
- no apparent changes
OR - possible widening of PDL
What is the radiographic appearance of initial spread of inflammation in periapical pathology?
Loss of lamina dura at apex
What is the radiographic appearance of further inflammatory spread in periapical pathology?
Periapical bone loss
What is the radiographic appearance of initial chronic inflammation in periapical pathology?
- No bone destruction seen
OR - dense sclerotic bone periapically (sclerosing osteitis)
What is the radiographic appearance of chronic, long standing, inflammation in periapical pathology?
- circumscribed, well defined, radiolucent area periapically with sclerotic bone surrounding
What is the radiolucency found in radiographs showing chronic inflammation of periapical pathology also described as?
Rarefying osteitis
What is quality assurance?
An organised effort by staff to ensure that the diagnostic images produced are of sufficiently high quality to consistently provide adequate diagnostic information at the lowest possible cost and the least possible exposure to the patient
What does SOP stand for?
Standard operating procedures
What are the 6 components of a quality assurance programme?
- image quality
- x-ray equipment
- processing
- working procedures
- training
- audit
What two ways can an image be audited to ensure high quality?
- Image quality rating system
- Film reject analysis
How could image quality rating systems grade images?
- rating diagnostically acceptable (A) or diagnostically not acceptable (N)
OR - rated either 1,2 or 3
What image would be given an image quality rating of 1:
- excellent
- diagnostically acceptable
- diagnostically unacceptable
Excellent
What image would be given an image quality rating of 3:
- excellent
- diagnostically unacceptable
- diagnostically acceptable
Diagnostically unacceptable
What image would be given an image quality rating of 2:
- diagnostically acceptable
- excellent
- diagnostically unacceptable
Diagnostically acceptable
what method in radiology can be used to measure exhaustion of the developer?
Sensitometry
What type of image would signify an exhausted developer?
A pale image
What is a step-wedge?
A radiographic phantom made from differing thicknesses of metal
What are the three most common problems faced during film processing?
- poor handling
- insufficient training
- light exposure
If a film is exposed to too much light during processing what will be the consequence?
Fogging of the film
What test can be used to monitor darkroom safelight conditions?
The coin test
What is a safelight?
A light with a coloured filter that can be used in a darkroom without affecting photosensitive film or paper
What are the four reasons why a radiographic image may appear very pale?
- wrong exposure selection ( underexposed image)
- not enough time in the developer
- developer temperature too low
- incorrect dilution of developer
Why might part of a film appear fogged?
- light leakage in darkroom
- incorrect handling of film
- patient movement
What would cause a film to turn green/yellow?
Insufficient fixing during processing, involving time, temperature and dilution.
What would be the cause of a film presenting with marks that resemble a lightening strike or a tree?
Caused by static electricity discharge, it is the result of pulling film too quickly out of packet in a dry atmosphere
Which three extra-oral images relating to the mandible are regularly seen?
- posterior-anterior mandible
- Lateral oblique of mandible
- DPT
Which three extra-oral images relating to the maxilla and cranium are regularly seen?
- Lateral cephalogram (skull)
- Occipito-mental views (face)
- Sailography
What does an ‘oblique’ angle mean?
Neither parallel nor at right angles to a specified or implies line: slanting
What does ‘PA’ stand for?
Postero-anterior
What does ‘AP’ stand for?
Antero-posterior
What does ‘OM’ stand for?
Occipito-mental
What are positioning landmarks?
A series of imaginary lines on the side of a patient’s face which are used to help position a patient for extra-oral radiography
Name the three main positioning landmarks
- Radiographic base line
- Frankfort plane
- Maxillary occlusal plane
Which positioning landmark matches the description below?
Line from outer canthus of the eye to the external auditory meatus, representing the base of the skull.
Radiographic base line
Which positioning landmark matches the description below?
Line from the ala of the nose to the tragus of the ear. This landmark is used a lot in cone beam CT.
Maxillary occlusal plane
Which positioning landmark matches the description below?
Line from the inferior orbital border to the upper border of the external acoustic meatus. Can also be known as the anthropological base line.
Frankfort plane
which positioning landmark is most often used when taking a DPT?
Frankfort plane
What are the components of equipment required for an extra-oral radiograph to be taken?
- Skull unit or cephalometric unit
- Image receptor
- Anti-scatter grid
- Lateral cephalogram unit
what does scatter of x-ray photons do to the final image?
Degrade or fog the image
What is an anti-scatter grid?
A grid made up of narrow strips of lead alternating with plastic, which limits the amount of scattered radiation reaching the detector/film
Why might a PA mandible be requested?
To look for potential fractures, cysts or malignancy causing medio-lateral displacement, expansion to bone destruction.
what extra oral radiograph is a PA mandible almost always requested alongside?
A DPT
What are the two main advantages of having a PA mandible taken over other extra-oral views?
- reduced magnification of facial structures on receptor
- reduced dose of radiation to eyes
How would a patient be positioned in regards to equipment if a PA mandible is to be taken?
- patient faces film
- nose and forehead touch film holder
- radiographic baseline should be 90 degrees to film
How do we find the ‘mid-line’ of the patient anteriorly and posteriorly?
Anterior: generally between the eyes
Posterior: at the external occipital protuberance
Why would we not just take a lateral mandible to visualise the mandible?
Because the two halves of the mandible will be superimposed
what way should you oblique the mandible in order to achieve full separation of the rami on the radiograph?
Oblique in the vertical plane
what are the indications for taking a lateral oblique mandible?
- fracture
- pathology
- assessment of wisdom teeth
- dental assessment in special needs patients
- caries in children who can’t tolerate bitewing
What are the two techniques used to take lateral oblique mandibles?
- Isocentric positioning using a skull unit
- Dental tube with either vertical or horizontal angulation
What is an isocentric technique?
Where all beams used in a radiation treatment have a common focus point, a.k.a the isocenter
What extra- oral view can be tricky to take on individuals with broad shoulders and why?
Isocentric view,
The skull unit is required to be angled at 25 degrees so that the x-ray tube moves towards the patients shoulder. If shoulders are broad they can get in the way of the beam.
What are the two disadvantages of vertical angulation of the dental tube when taking lateral oblique mandibles?
- Angulation can cause vertical distortion of the teeth
- Maxillary teeth are not always shown clearly
What angulation of the dental tube is most common when taking a lateral oblique mandible?
Horizontal or vertical?
Horizontal
Which angulation of the dental tube when taking a lateral oblique mandible, aims through the radiographic keyhole?
Vertical or horizontal?
Horizontal
what is the radiographic keyhole?
The triangular space between the back of the ramus and the cervical spine
What is the disadvantage of horizontal angulation of the dental tube when taking lateral oblique mandibles?
X-ray beam may not pass directly between the contact points of the teeth therefore causing them to be overlapped on the film
What is a standardised and reproducible form of skull radiography in orthodontics, to assess the relationship of the teeth to the jaws, and the jaws to the rest of the facial skeleton?
Cephalometric radiography
What are the two main indications of cephalometric radiography?
- Orthodontic assessment
- Pre-orthodontic surgery
In a lateral ceph where is the x-ray beam aimed?
At the external acoustic meatus
what is a thyroid shield and what is it used for?
Lead collar that wraps around your neck to block the radiation that’s generated when taking a radiograph
What does a magnification rod, found in ceph films, allow for and why is it necessary?
Allows for the calculation of any magnification that has occurred on the final image and is necessary for surgical planning
The exposure required to penetrate a lateral face/skull is so great, in normal circumstances the beam would not be attenuated at all by the soft tissues, so they would not be visible on the image. What can be used to overcome this and allow soft tissues to be visualised on a lateral ceph?
An aluminium filter
What are the main indications for x-raying facial bones?
- trauma and suspected fracture
- pathology
what are the most common fractures to the facial bone?
Zygoma, le fort and orbital blowout
what are the three different angles of occipito-mental views used to view different areas of complex facial bone anatomy?
- OM 0 degrees
- OM 10 degrees
- OM 30 degrees
What view is taken for imaging of facial bones?
Occipito-mental views
What should the radiographic baseline to film angle be for OM views?
45 degrees to film
What is caudal angulation?
How you would raise the x-ray tube to angle the central ray
What are the two main benefits of increasing angulation on OM views?
- Projects dense bones of skull base down and away from facial structures
- Improves view of zygomatic arch
when wanting to visualise the zygomatic arches, which OM view is the best to use?
OM 30 degrees
What does a star on a radiographic image indicate?
There is a fracture indicated by radiographer who took image.
what is a tomogram?
A radiograph showing a slice or section of tissue in focus
What is a form of tomography used in dentistry?
DPT
Only structures within what area/slice are sharp on a DPT image?
The focal trough
what shape is the focal trough?
Horse-shoe shaped
what are the three disadvantages of intensifying screens within conventional film cassettes?
- Light is emitted in all directions
- Light affects larger area of film than a single photon
- Image quality (fine detail) is not as good as direct action film
When taking a DPT, what does use of a bite peg do?
- Forces patient into edge-to-edge occlusion
- positions both arches in focal trough
what are the main advantages to taking a DPT over a periapical?
- Can capture entire dentition in once image
- Able to image non-dental areas
- Lack of intra-oral holders benefits some patients
What are some key clinical indications for taking a DPT?
- orthodontic assessment
- mandibular fractures
- degenerate disease of TMJ
- implant planning or review
- symptomatic third molars
What are the main disadvantages of taking a DPT over a periapical?
- lack of fine detail
- superimposition
- more artefacts
- patient co-operation required
- exposure time up to 16 seconds
- higher radiation dose per image
describe the patients position when taking a DPT
- Stands with spine straight, holding handles
- Bites incisors edge to edge on bite block
- Head immobilised
- Tongue to roof of mouth
- Stand still
- Do not talk or swallow
Why should we not routinely use lead aprons in dental radiography?
Because they do not protect from internal scatter and they interfere with image as can be projected onto image and may also catch the tube as it rotates
What is an example dose of radiation from a DPT?
3.85-30 micro Sv
what are ghost images?
Images of a structure on one side which are projected onto other side
why are ghost images always seen at a higher level than the real structure?
Because the x-ray beam is pointing upwards at an angle of 8 degrees to the horizontal
what incisors relationship does not allow for a patient to correctly bite upon a bite block?
Class III incisal relationship- where mandibular incisor is anterior to maxillary incisor
What does ‘collimated’ mean?
To make parallel
When a patient has a strong gag reflex, what radiograph is most likely to be taken?
DPT
Why is superimposition not as bad in intra-oral x-rays compared to extra-oral x-rays?
As intra-oral x-ray source and receptor can both be placed close to area of interest ( therefore fewer structures are captured, less superimposition)
What form of radiography try to counteract superimposition?
Tomography
what type of tomography, involving multiple slices is commonly used in medicine?
Computed tomography
What type of tomography is a Panoramic radiograph?
Conventional tomography
Where is the x-ray source in comparison to the patient during a DPT?
Behind
Where is the receptor in comparison to the patient during a DPT?
In front
Describe the characteristics of an x-ray beam used for DPT
Narrow, vertical, “fan-shaped”
why is it common for the incisor region to appear blurry on a DPT?
Because the focal trough is thinner in this region
What does “orthogonal” view mean?
A 90 degree view horizontally or vertically
What are the advantages of the x-ray beam angulation being changed to a more orthogonal view in order to visualise teeth?
- reduces overlap of the teeth to aid assessment of approximal caries (particularly improves premolars)
- improves angulation to better represent interdental periodontal bone levels
What are the disadvantages of the x-ray beam angulation being changed to a more orthogonal view in order to visualise teeth?
- distorts the rest of skeleton
- typically a narrower field of view so may miss condyles on edge of image
How much is the image within the focal trough magnifies by?
Around 25%
Which structures in relation to the focal trough are more magnified?
Lingual or buccal
Lingual
Which structures in relation to the focal trough are less magnified?
Lingual or buccal
Buccal
How do teeth positioned buccal to the focal trough appear on an image?
Narrower (vertical magnification)
How do teeth positioned lingual l to the focal trough appear on an image?
Broader (horizontal magnification)
Why are structures within the focal trough not distorted?
Because the degree of horizontal magnification matches that vertically
Where is the x-ray source positioned in comparison to the focal trough?
Lingually
By how many times is the radiation dose greater per DPT image compared to periapical image?
5 times
What is the ‘field limitation’?
Changing size of x-ray field to reduce radiation does
What are the three light beam markers used to take DPT?
- horizontal line: Frankfort plane
- vertical mid-line: mid-sagittal plane
- vertical canine lines
If the Frankfort plane is out of position due to the chin of the patient being down, how will this reflect on the image?
The occlusal plane will appear ‘smiling’
If the Frankfort plane is out of position due to the chin of the patient being up, how will this reflect on the image?
“Flat” occlusal plane
If the mid-sagittal plane is not centered, how will this reflect on the image?
Distortion of one/both sides of image
If the mid-sagittal plane is out of position due to incorrect vertical alignment, how will this reflect on the image?
Distortion and occlusal plane cant
If the mid-sagittal plane is out of position due to the patient being slumped over, how will this reflect on the image?
Excessive cervical spine shadow
If patient does not press tongue against palate while DPT is being taken, how will this reflect on the image and why?
A black radiolucent band across the maxilla will appear as an air gap has been created between the tongue and roof of mouth
What are the 6 different structures that make up the mandible and can be seen clearly on a DPT?
- condyle
- coronoid process
- sigmoid notch
- ramus
- angle
- body
How does the submandibular fossa present on a radiograph?
As a depression on the lingual aspect of the body of the mandible
Why does the mastoid process sometimes appear as having a ‘honeycomb’ pattern on a radiograph?
Because it is filled with trabecular bone
What is the purpose of the articular eminence?
Stops condylar head from moving forward out of the glenoid fossa
Why are misleading shadows created on DPT’s?
Due to the rotational technique, the resulting panoramic image also exhibits abnormal structures
What are the two types of misleading shadow?
- Double shadows
- Ghost shadows
What are double shadows and how are they created?
Created by structures located near the centre of rotation which, due to their central position, are captured twice (i.e. x-ray machine passes through them twice as it spins round head)
what three anatomical structures commonly have a double shadow?
- Hyoid bone
- Soft palate
- Cervical spine
What are ghost shadows and why are they created?
Structures on one side are projected onto the other side. Created by structures between the x-ray source and the centre of rotation
Why do ghost shadows always appear higher than where the structure should actually be?
Due to the inclination of the x-ray beam and that it is transposed on to the opposite side of the true anatomical position
Why are DPT’s poor for showing anterior fractures of the mandible?
Due to superimposition of ghost shadow of cervical spine
What type of radiographic image can be created which cuts out areas we aren’t interested in and therefore less anatomical areas are radiated?
Panoramic pseudo-bitewing image
What scale is used to quantitively measure radio-density on CT scans?
Hounsfield scale
What is a “voxel”?
Volume of pixel
What does orthognathic assessment/surgery mean, in simpler terms?
Jaw assessment/surgery
What are the 7 main indications for use of a CT scan?
- Intracranial assessment
- Trauma
- Evaluation of osseous lesions
- Salivary gland assessment
- Cancer screening
- Orthognathic assessment
- Implant planning
What is Dentascan?
A specialised CT scan of the mandible or maxilla often done before placement of dental implants
What is the main indication for using CBCT over CT?
CBCT has a much lower radiation dose than medical grade CT
What does CBCT stand for?
Cone-beam computer tomography
Prior to a CBCT scan being performed, an initial positioning view is usually taken. Why is this?
This ensures that the area of concern is in the field of view
For a CBCT, are the x-ray tube and flat panel receptor rotating in different directions or the same direction?
Same direction
In a CBCT scan which x-ray component sends the information to the computer where an image will be produced?
Receptor
For CBCT, if multi-planar imaging is available, what are the three slices that will be displayed?
- Axial
- Coronal
- Sagittal
What are the four main indications for taking a CBCT?
- Localisation of unerupted tooth
- Assessment of resorption from unerupted tooth
- Cleft palate
- Orthognathic surgery assessment
What field of vision should dental practices use?
Small
What does the unit mA stand for and what does it represent?
Milliamperes, represents the amount of current passed through the x-ray tube
What is spatial resolution?
The number of pixels utilised in construction of an image
What does field of view mean (FOV)?
The open, observable area a person can see through their eyes or via an optical device, such as a camera
what is the benefit of taking an I-CAT panoramic scan?
Allows you to take complete 3D images at a radiation dose comparable to a 2D panoramic image
What are 4 imaging modalities that are hardly, if ever, used in general dental practices, however hospital dental specialists may request them?
- MRI
- Ultrasound
- Nuclear medicine (radio-isotope scanning)
- PET
What is a blow-out fracture?
Fracture of the orbital floor, causing orbital contents to herniate into the sinus
What is the main benefit and also the mian disadvantage to a smaller CBCT voxel being used?
Benefit: results in a higher resolution image
Disadvantage: requires longer scan time and therefore a higher dose required
What is the axial plane?
Also known as the transverse plane, it is a horizontal plane that divides the body part into superior and inferior sections
What is the coronal plane?
Also known as frontal plane, it divides the body part into front and back sections
What is the sagittal plane?
Also known as the longitudinal plane, it divides the body into right and left sections
What is MRI?
Magnetic resonance screening is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body
what type of tissue is MRI useful for assessing?
Soft tissue
What are the main contraindications of MRI use?
- pacemakers
- artificial heart valves
-intra-cerebral aneurysm clips - 1st trimester pregnancy
- claustrophobia
In what patient cases would it be suitable to refer for MRI?
- TMJ disorders (particularly disc problems)
- salivary gland pathology
- assessing early bone changes if there is suspected medication-related osteonecrosis of the jaw
how does an ultrasound work?
- Transducer placed o skin
- Sound waves bounce off tissues and back to probe
Ultrasound can travel beyond hard tissues. True or false?
False
what is radio-isotope scanning?
An imaging technique where small dose of isotopes are injected into the body and emit radiation in order to detect changes in target tissue
what is technetium?
The lightest chemical element whose isotopes are all radioactive
what chemical element foes radioisotope scanning use?
Technetium
what is a PET CT scan?
Position emission tomography combined with CT
When would a PET CT scan be used?
To diagnose and stage cancer
Who discovered x-rays?
Wilhelm Conrad Roentgen
What year were x-rays discovered?
1895
Name the law that gives us the safe distance from a source of x-rays
Inverse square law
What does the photoelectric effect do?
The emission of electrons when light shines on a material
What does IR(ME)R 2000 stand for?
Ionising radiation (medical exposure) regulations 2000
what does IRR 2017 stand for?
Ionising radiation regulations 2017
How does IRMER 2017 differ from IRR 2017?
IRMER 2017 deals with exposure to patients for medical and non-medical procedures, whereas IRR 2017 deals with exposure to employees and the public
What does RPA stand for? And what do they do?
Radiation protection advisor, is an individual or body that advises on compliance with the IRRs
What does RPS stand for? And what do they do?
Radiation protection supervisor, a person/s appointed for the purpose of securing compliance with the IRRs in respect to work carried out in an area which is subject to local rules
Name the 4 designated roles under IR(ME)R 2017
- Employer
- Referrer
- Practitioner
- Operator
Which designated role in IRMER deals with legalities of taking x-rays?
Employer
What is the designated role of the practitioner under IRMER 2017?
Justifies the exposure
Who is the “operator” according to IRMER 2017?
Any person involved in the “practical aspects” of the production of a radiograph.
what are local rules?
Written rules pertaining to controlled areas where the appropriate procedures are to be followed and responses to incidents or accidents involving ionising radiation.
What does MPE stand for?
Medical Physics Expert
what is the role of an MPE?
Responsible for carrying out dose audits to ensure that dose optimisation and risk education is being correctly achieved
What is the duty of the employer regarding selection criteria for radiographs?
Shall establish recommendations concerning referral criteria
What are the three main advantages of using the paralleling technique for intra-oral radiographs?
- Allows accurate geometry of image
- Rectangular collimator is easier to position
- Can reduce dose to patient by reducing repeats and does not expose patients fingers
What age of patient is more radiosensitive? 0-18 or 50 +. And why?
0-18, because young patients have more dividing cells and a longer lifespan over which to develop effect
What are the two main roles of the “employer”?
- Establishing QA programmes for standard operating procedures
- Ensuring that every practitioner undertakes CPD
How much CPD must every practitioner or operator prove that they have undergone every 5 years?
5 hours
What are the tow recommended radiographic techniques for diagnosing caries?
Horizontal bitewings ( gold standard)
Paralleling periapicals
What are the two disadvantages of taking a lateral oblique mandible?
- Angulation can cause vertical distortion of teeth
- Maxillary teeth are not always shown clearly
what type of radiograph requires a thyroid shield for lead protection as the exposure factors required and consequent dose are slightly greater?
Lateral cephalogram
What filter is used in a lateral cephalogram to allow visualisation of bone and soft tissue on the film?
Aluminium filter
what was the ‘three tier approach’ that IRR17 introduced that IRR99 did not have?
- Notification
- Registration
- Licensing
How do RPA and MPE differ?
RPA has a role in IRR17, MPE is part of IRMER17 ( though could be the same person!)
