Radiation Physics Flashcards
What are the ironising radiation medical exposure regulations (IRMER)
Concerns Patient protection and it’s enforced by the care quality commission (CQC)
What do the IRMER regulations apply too?
Patient exposure
Volunteer exposure
What is the IRMER philosophy
Avoid unnessicary exposure Every exposure must have net benefit Optimise exposures Ensure quality of exposures Written clinical evaluation Define responsibilities or operators etc
What must medical radiation equipment do
Capable or restricting exposure to a patient
Fitted with an indicator of radiation
Subject to lots of testing
Subject to quality assurance testing
What happens in quality assurance?
Measure the dose and check it matches with what the devices says
What are the main 2 IRMER principles
X-rays must have net benefit
X rays must be in as low as reasonably practical
What must the employers procedures include IRMER
There must be written procedures for referees pro action era and operators. Justification for medical exposure. Non medical exposure procedure Pregnant patients Career exposure Written standard operating protocols Clinical evaluation Diagnostic reference levels Audit review
What is the IRMER referrer
Anyone the employer decides is entitled to refer, could be dentists, GP or healthcare professional.
Referred must provide significant and correct information to identify the patient and clinical information justifying the X-ray
Must be provided with written criteria
IRMER Practitioner
Anyone the employer decides can justify a dental radiograph
Only clinically justified
Justification must be written prior to exposure
Process must identify individual response
Radiograph only based on referrals info practitioner must justify and authorise
IRMER who is the operator
Anyone who operates on the outcome of the successful medical exposure is an operator Dentist Nurse Hygienist Physics staff Responsibilities must be clearly defined
IRMER operator role
Optimise exposure Balancing act between as little as possible exposure but successful radiograph Ensure correct patient Ensure correct examination Ask about pregnancy Use right exposure factors Position patient correctly Minimise field size
IRMER training
Practitioners and operators schedule 3 training
Theoretical knolage relevant to function such as radiation physics management or radiation protection
IRMER patient ID procedure
The patient must be identified before exposure
Ask name DoB and address
If they cannot correctly ID then the patient will be sent back to the referrer
It’s the operators responsibility to do this
What is the legislation of IRMER and pregnancy
No one should carry out radiograph unless there is sufficient net benefit
What are the diagnostic reference levels
Guide the acceptable levels of dose, there are nationally set levels of patient dose thes can be exceeded in individual cases investigated when the are exceeded routinely
What is the average patient entrance dose (PED) for an adult then child
Adult 1.37
Child 0.63 mGy
What is the effective dose
Adults 4 uSv
Children 1 uSv
What is the average dose of area product (DAP)
Adult 80
Child 56 mGy.cm2
Effective dose or area product
Adult 10
Child 6 uSv
What is the national diagnostic reference level for DAP
Adult 93
Child 67
IRMER image evaluation
Carried out and recorded including info on dose etc
IRMER audit
All policies must be regularly gone over proving they still work
Clinical audit must be carried out proving it (process) still work
Audit includes procedures are being followed
Quality control of processing
Percentage scoring in levels of images
Written evaluation and comparison with previous audit
IRMER investigations?
Patient exposure much greater then intended
Equipment malfunction and unintended exposure
If you think a larger exposure occurs to staff or patient it must be recorded
Incidents: Wrong person named on request Wrong patient Appointment letter goes to the wrong patient Not following identification procedure
Doing the wrong x Ray
Duplicated request card or being used twice
IRMER17?
This is emphasis on optimisation.
Registration and certification
Requirement for patient dose and monitoring.
Applies to basically anyone
Dose constraintis
Population dose monitoring
Accidental exposure policy must be in place
Estimation of population dose reported to secretary of state
Physics people advice in complacency with this regulation
It all go tributes to safe practise
What is IRR
Ionising radiation regulations 2017
Concerned with the protection of employees and general public
WiFi ever by the health and safety executive
IRR guidance
There are guidance notes for dental practitioners it’s a framework including ALARP principle
Flow charts should be created
What is a radiation protection adviser
Employer must consult this persons to be approved by the HSE
Check that employer is following correct regulations etc
Who are classified persons
People who are likely to receive a very high does over 6 throughout whole body
Investigation level
The employer must investigate wether an employees dose is more that 15mSv during a year
Hospitals normally set a lower threshold
Dental radiation controlled areas
Dedicated x Ray room
Or dental x ray sign meaning x rays 1.5m in any direction
Radiation controlled areas
Marked out restrictive monitoring
Power switch outside the room ensure patient safe equipment labels out of order
Define:
Radiology
Radiography
Radiation protection
Interpretation of the image
Techniques involved in producing an image
Protecting staff and patient
What’s a periapical radiograph
Includes full tooth
Bitewing?
Upper and lower crowns (common)
Upper and lower occlousals?
These are the odd ones that get the full arch (upper or lower)
Panoramic?(pantomogram)
What it says
Lateral cephalogram
This is extraordinary of the side profile of the full head
What are interesting anatomical marks seen in radiographs
Incisive foramen Canine fossa Floor of nasal cavity Y shape of Ennis (runs above tooth roots) Floor of maxillary Antrum (floor of sinus septum) Zygomaticus Pterygoid hamulus Coranoid process Submandibular fossa IA canal Mental foramen Lingual foramen
What are the layers of a direct action film
Plastic base (cellulose acetate)
adhesive
Emulsion (both sides of base silver halide)
Protective layer (gelatine)
Outer packet protects from saliva
Black paper lining (stops light exposure)
Lead foil absorbs radiation and prevents backscatter onto film
What is the detection film orientation
Embossed dot on one corner
Raised dot placed facing the X-ray because
Raised dot at occlousal plane for periapical
What’s an indirect action film
Has intensifying screen in a cassette Intensifying screen emits light photons Film sensitive to light This is used for extraoral radiographs Silver halide is reactive to light (blue) Modified halides react to all light
Intensifying screen contains fluorescent phosphors convert x Ray energy into light photons by photoelectric affect
Different phosphors different colours
What’s a cassette
House image director and intensifying screen
They are light tight aluminium or carbon fibre
Film is between to intensifying screens
Sponge layer ensures smooth contact between film and screen.
How is the film processed
Developed Washings Fixation (unsensitised crystals removed) washing (removes fixer solution) Drying
The lack is where it has been sensitised and the black fixer sticks
What is film speed
This is the speed that the film takes to respond the the x Ray photons it’s related to the amount of crystals and there size in the emulsion.
Faster the larger the crystals
Faster the lower the dose
Always use fastest film
What is optical density
This is the degree of blackening in a radiograph
In diagnostic radiology the OD is 0.25-2.5
What is fog
This is the degree of blackening with zero exposure caused by plastic base if development of u exposed crystals
Fog density should be less than 0.2
What are the characteristics of image receptors
Characteristic curve (variation in OD leads to different exposures) Latitude range of exposures that cause a different OD Average gradient if it’s high good contrast but narrow latitude if low poor contrast but large latitude
What are digital receptors used for
Periapical or bitewing
Extraoral
Occlousal and lateral obliques
How is the digital image made
Captured in pixels
Each pixel represents a cube (voxel)
Each pixel measures he total absorb ace through that cube
Each cube given a grey scale value there are 256 options of the scale (black)0-255(white)
What’s a solid state sensor ccds
Direct digital is a charge coupled device with silicone chips embedded in an electrical circuit.
These pixels arranged in rows called and array or matrix.
Surface scintillation layer of rare earth type material most have wire or cable linking to computer
How does a solid state sensor work
X-ray photons hit scintillation layer and are converted to light which interacts with silicone via photoelectric affect.
Creates a charge packet which is concentrated by electrodes this is sent to the computers analogue to digital converts to make the image
That is a solid state sensor (cmos)
Complementary metal oxide detectors these are like the ccds but each pixel is separated from the one around it
Charge packet from each pixel is transferred directly to transistor as a voltage
Allows each pixel to be assessed separately
What are the good and bad of solid state sensors
Immediate image viewing
Not autoclavable so require protective film
Smaller detector surface than film
Bulky detector and wire
Wireless are bulkier due to extra electronics
What do extraoral digital sensors do how are the made
Have long thin linear arrays
Scanning motion
What are photostimulable phosphor storage plates
Similar to film (range of sizes)
Wireless
Reusable
Protective embolisms used for cross infection
Barium flurohalide phosphor on a flexible plastic backing the phosphor layer absorbs and stores the X-ray energy image which’s is scanned by laser then the light is released which is converted to a voltage and related by the computer
What does a narrow window mean (low number)
Less grey shades more contrast
Higher is more grey shades and greater contrast
What’s scatter
This is where photons scatter and cause overall darkening if the image
How is contrast effected
Determined by average slope of the useful part of the characteristic curve
Steeper slope = higher contrast
Affected by exposure processing and background fog
Viewing in monitor reduction in ambient light helps see contrast
What happens if film image is too pale
Too dark
Too short developing Too cold Too dilute Exhausted developer Underexposed
Too long in developer Too concentrated developer Too hot Fogged Over exposed
Resolution
Ability if a system to differentiate objects to close together
Can be influenced by penumbra
What is a penumbra
How is it reduced
Area of partial shadow along object caused by diverging X-ray photons
Object close to receptor
Decreasing focal spot size
Increasing focal spot to detector distance
What’s distortion
This is where magnification is different in different parts of the object
Arises when the film is not parallel to the object when the X-ray beam is not perpendicular to the receptor.
Can cause foreshortening and elongation
What is bad about intensifying screens
Amplify photons and cause them to spread out
How do digital images become blurry
If a pixel lies on a border it will come out a colour in the middle causing blur
How much radiation that’s man made comes from medical
How much radiation is manmade
97%
16.5%
What is the average annual diagnostic dose
440uSv
What is the current opinion on radiation
Harmful in any dose but benefit will outweigh the risk
What are the three things that happen with radiation when fired at a human
Transmitted (allows us to see radiographs)
Absorbed (harmful)
Scattered harm to others
When are cells most vulnerable to radiation
In the replication stage more active cells with higher replication rates are more vulnerable
How does radiation damage cells
Causes ionisation of water to form molecules that can damage chromosomes like free radicals
What’s deterministic exposure
High dose over short time causes radiation sickness would not occur in dental radiology
What’s stochastic exposure
Occur at high and low doses causing chronic and potentially long term effects.
What dose causes deterministic effects?
1000 mSv or above
What is the current view of cancer and radiation
That cancer risk is 1 in 20000 per mSv
Risks in kids higher then the elderly
Hereditary risk is 1 in 100000 per mSv
What are the risks of a dental x Ray
1 in 20000 rush of fats cancer for each 1mSv radiation
What are the ICRP principles for protection
Limitation
Justification
Optimisation
What are the effective doses for and adult and child
- 004 mSv
0. 001 child
The risks of cancer from dental intraoral
Less than 1 in 6 million
What’s a bitewing
Shows the crowns with minimal enamel overlap
Half thickness of enamel is acceptable
Used to detect aproximal occlusal recurrent caries
Check for calculus deposits
How do you take a bite wing
Use film holder long axis of film horizontal use size 2 film film as close to teeth as possible
What’s a vertical bitewing
Long axis of film is vertical shows more alveolar bone
What’s good about a film holder
And bad
Simple
Not displaced by tongue
Beam always right angle to film
Uncomfortable
Expensive
What’s the adhesive tab technique
This is where original tab attached to the middle of the film at a right angle and patient would bite on it. It’s still good for kids
What’s a periapical
Shows all of tooth used for trauma abscess infection endo etc
It has to be further away from tooth due to anatomical things film size 1 or 2
What’s the paralleling technique
This is where everything is parallel to the root of the tooth to make a sharp and true image approximately caries well show.
What’s the bisecting angle technique
Film not perpendicular to beam it’s at and angle this causes elongation etc
Irradiated ginger when doing occlousals from holding film in place
Bone levels not accurate
What are occlousals
Image of an occlousal arch dot faces arch being imaged can assess impacted teeth etc used for trauma. Or submandibular duct stones
True is where beam is perpendicular
Oblique is where the beam is at an angle
Maxillary oblique?
Take down through tip of nose at 60-70 degree angle
Mandubular true occlousal
Up through the mandible
Lower anterior occlousal
Fired from front of face up through jaw at 45 degree to the film
Lower oblique occlousal
Fired up through the jaw from one side
What’s eV
Electron volt
What’s photon energy
E=he/y
How is a bremsstrahlung X-ray made
Electron does not collide flies round the nucleus of an atom and emits X-ray
How are characteristic xrays produced
Electron removed from inner shell
Electrons from outer shell have to move inwards for this emoting xrays.
What are the X-ray tube components
Cathode (electron source) Anode target Glass envolope filters Cooling oil Shield
What does the evacuated glass tube do
No other atoms for electrons to interact with provides insulation between anode and cathode
What does the metal shield do
Stops xrays flying everywhere
What does the window do
The area that the xrays emerge
What is electron energy proportional to
Voltage (kV)
What is the robe potential
KVp quantity if xrays and intensity
What is the tube current
Electrons flowing from the cathode to anode can be measured in miliamps mA
What is x Ray intensity proportional too
Tube current
What’s filtration
Removes low energy photons reduces patient dose
Filtered has lower intensity but greater average photon energy
What size focal spot do you want.
Small to make a sharper image
What is attenuation
This is the overall reducing I tensity of an x Ray
What’s the photoelectric effect
Photon collides wit an electron and causes it to give up all its energy and it no longer exists
What’s the Compton scatter effect
This is where photon collides wit and electron then gives it some energy and bounces off in a different direction causing scatter
What does Compton scatter cause
Reduced sharpness image
How is scatter avoided
Specific range of x rays 30/
-70
Reduce kV (this increases dose )
Anti scatter grids
How do you reduce noise
Increase the number of x Ray photons
What does magnification do
Increases dose and all the other things
