Radiation Physics Flashcards
(112 cards)
1
Q
What are the ironising radiation medical exposure regulations (IRMER)
A
Concerns Patient protection and it’s enforced by the care quality commission (CQC)
2
Q
What do the IRMER regulations apply too?
A
Patient exposure
Volunteer exposure
3
Q
What is the IRMER philosophy
A
Avoid unnessicary exposure Every exposure must have net benefit Optimise exposures Ensure quality of exposures Written clinical evaluation Define responsibilities or operators etc
4
Q
What must medical radiation equipment do
A
Capable or restricting exposure to a patient
Fitted with an indicator of radiation
Subject to lots of testing
Subject to quality assurance testing
5
Q
What happens in quality assurance?
A
Measure the dose and check it matches with what the devices says
6
Q
What are the main 2 IRMER principles
A
X-rays must have net benefit
X rays must be in as low as reasonably practical
7
Q
What must the employers procedures include IRMER
A
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
8
Q
What is the IRMER referrer
A
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
9
Q
IRMER Practitioner
A
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
10
Q
IRMER who is the operator
A
Anyone who operates on the outcome of the successful medical exposure is an operator Dentist Nurse Hygienist Physics staff Responsibilities must be clearly defined
11
Q
IRMER operator role
A
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
12
Q
IRMER training
A
Practitioners and operators schedule 3 training
Theoretical knolage relevant to function such as radiation physics management or radiation protection
13
Q
IRMER patient ID procedure
A
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
14
Q
What is the legislation of IRMER and pregnancy
A
No one should carry out radiograph unless there is sufficient net benefit
15
Q
What are the diagnostic reference levels
A
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
16
Q
What is the average patient entrance dose (PED) for an adult then child
A
Adult 1.37
Child 0.63 mGy
17
Q
What is the effective dose
A
Adults 4 uSv
Children 1 uSv
18
Q
What is the average dose of area product (DAP)
A
Adult 80
Child 56 mGy.cm2
19
Q
Effective dose or area product
A
Adult 10
Child 6 uSv
20
Q
What is the national diagnostic reference level for DAP
A
Adult 93
Child 67
21
Q
IRMER image evaluation
A
Carried out and recorded including info on dose etc
22
Q
IRMER audit
A
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
23
Q
IRMER investigations?
A
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
24
Q
IRMER17?
A
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
25
What is IRR
Ionising radiation regulations 2017
Concerned with the protection of employees and general public
WiFi ever by the health and safety executive
26
IRR guidance
There are guidance notes for dental practitioners it’s a framework including ALARP principle
Flow charts should be created
27
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
28
Who are classified persons
People who are likely to receive a very high does over 6 throughout whole body
29
Investigation level
The employer must investigate wether an employees dose is more that 15mSv during a year
Hospitals normally set a lower threshold
30
Dental radiation controlled areas
Dedicated x Ray room
| Or dental x ray sign meaning x rays 1.5m in any direction
31
Radiation controlled areas
Marked out restrictive monitoring
| Power switch outside the room ensure patient safe equipment labels out of order
32
Define:
Radiology
Radiography
Radiation protection
Interpretation of the image
Techniques involved in producing an image
Protecting staff and patient
33
What’s a periapical radiograph
Includes full tooth
34
Bitewing?
Upper and lower crowns (common)
35
Upper and lower occlousals?
These are the odd ones that get the full arch (upper or lower)
36
Panoramic?(pantomogram)
What it says
37
Lateral cephalogram
This is extraordinary of the side profile of the full head
38
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
```
39
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
40
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
41
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
42
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.
43
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
44
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
45
What is optical density
This is the degree of blackening in a radiograph
| In diagnostic radiology the OD is 0.25-2.5
46
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
47
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
```
48
What are digital receptors used for
Periapical or bitewing
Extraoral
Occlousal and lateral obliques
49
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)
50
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
51
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
52
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
53
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
54
What do extraoral digital sensors do how are the made
Have long thin linear arrays
| Scanning motion
55
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
56
What does a narrow window mean (low number)
Less grey shades more contrast
Higher is more grey shades and greater contrast
57
What’s scatter
This is where photons scatter and cause overall darkening if the image
58
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
59
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
```
60
Resolution
Ability if a system to differentiate objects to close together
Can be influenced by penumbra
61
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
62
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
63
What is bad about intensifying screens
Amplify photons and cause them to spread out
64
How do digital images become blurry
If a pixel lies on a border it will come out a colour in the middle causing blur
65
How much radiation that’s man made comes from medical
How much radiation is manmade
97%
| 16.5%
66
What is the average annual diagnostic dose
440uSv
67
What is the current opinion on radiation
Harmful in any dose but benefit will outweigh the risk
68
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
69
When are cells most vulnerable to radiation
In the replication stage more active cells with higher replication rates are more vulnerable
70
How does radiation damage cells
Causes ionisation of water to form molecules that can damage chromosomes like free radicals
71
What’s deterministic exposure
High dose over short time causes radiation sickness would not occur in dental radiology
72
What’s stochastic exposure
Occur at high and low doses causing chronic and potentially long term effects.
73
What dose causes deterministic effects?
1000 mSv or above
74
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
75
What are the risks of a dental x Ray
1 in 20000 rush of fats cancer for each 1mSv radiation
76
What are the ICRP principles for protection
Limitation
Justification
Optimisation
77
What are the effective doses for and adult and child
0. 004 mSv
| 0. 001 child
78
The risks of cancer from dental intraoral
Less than 1 in 6 million
79
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
80
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
81
What’s a vertical bitewing
Long axis of film is vertical shows more alveolar bone
82
What’s good about a film holder
| And bad
Simple
Not displaced by tongue
Beam always right angle to film
Uncomfortable
Expensive
83
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
84
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
85
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.
86
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
87
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
88
Maxillary oblique?
Take down through tip of nose at 60-70 degree angle
89
Mandubular true occlousal
Up through the mandible
90
Lower anterior occlousal
Fired from front of face up through jaw at 45 degree to the film
91
Lower oblique occlousal
Fired up through the jaw from one side
92
What’s eV
Electron volt
93
What’s photon energy
E=he/y
94
How is a bremsstrahlung X-ray made
Electron does not collide flies round the nucleus of an atom and emits X-ray
95
How are characteristic xrays produced
Electron removed from inner shell
| Electrons from outer shell have to move inwards for this emoting xrays.
96
What are the X-ray tube components
```
Cathode (electron source)
Anode target
Glass envolope filters
Cooling oil
Shield
```
97
What does the evacuated glass tube do
No other atoms for electrons to interact with provides insulation between anode and cathode
98
What does the metal shield do
Stops xrays flying everywhere
99
What does the window do
The area that the xrays emerge
100
What is electron energy proportional to
Voltage (kV)
101
What is the robe potential
KVp quantity if xrays and intensity
102
What is the tube current
Electrons flowing from the cathode to anode can be measured in miliamps mA
103
What is x Ray intensity proportional too
Tube current
104
What’s filtration
Removes low energy photons reduces patient dose
| Filtered has lower intensity but greater average photon energy
105
What size focal spot do you want.
Small to make a sharper image
106
What is attenuation
This is the overall reducing I tensity of an x Ray
107
What’s the photoelectric effect
Photon collides wit an electron and causes it to give up all its energy and it no longer exists
108
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
109
What does Compton scatter cause
Reduced sharpness image
110
How is scatter avoided
Specific range of x rays 30/
-70
Reduce kV (this increases dose )
Anti scatter grids
111
How do you reduce noise
Increase the number of x Ray photons
112
What does magnification do
Increases dose and all the other things
