Past paper MCQ Flashcards
1
Q
The personnel involved in dental radiographic examination occur in following order?
A
- Referrer, practitioner, operator
2
Q
In radiographic localisation the acronym SLOB stands for?
A
- Same lingual Opposite buccal
3
Q
The probability of photo-electric absorption effects occuring in radiography is proportional to?
A
- Atomic number Z3
4
Q
What is the correct colour of film holder to use when taking PA 26?
A
- Yellow
5
Q
Radiograph colour for PA 11?
A
- Blue
6
Q
Radiograph colour for endo?
A
- Green
7
Q
Radiograph colour for bitewings?
A
- Red
8
Q
In relation to Ionising radiation regulations 2017 what is true?
A
- Practitioner must justify every exposure
9
Q
When positioning patient for panoramic radiograph (OPT) what anatomical reference should be horizontal ?
A
- Frankfort plane
10
Q
What is the most likely processing fault in a radiographic image which is too dark?
A
- Too much time in developer
11
Q
How often should a test film be exposed and processed in GDP for quality assurance?
A
- Daily
12
Q
When positioning pt for upper anterior oblique occlusal radiograph, what anatomical reference is used to assess occlusal plane?
A
- Ala-tragus line
13
Q
A lateral cephalometric radiograph is taken for a pt requiring what orthodontic treatment?
A
- Functional appliance therapy
14
Q
In dental panoramic radiography what should x-ray beam be?
A
- Aimed upwards at approx 8degrees
15
Q
Intra-oral charge coupled devices (CCD) digital x-ray sensors are what?
A
- More sensitive to x-rays than F-speed film
16
Q
What occurs in radiographic tube head?
A
- Interacts with target to produce characteristic and continuous radiation
17
Q
What is occuring between the electrons in the tube head?
A
- Electrons from tungsten anode to interacting with tungsten cathode
18
Q
What is the most important part when you send the pt down for radiographs to radiology>
A
- Clinical justification
19
Q
What curve affects radiographic technqiue?
A
The curve of spee affects vertical angulation
20
Q
What is the frequency of radiographs for high risk adults?
A
6 months
21
Q
What distance should the beam aiming device be from the skin?
A
- 1-2cm
22
Q
What is the best way to identify a pt arriving at radiology?
A
- Ask for their details
23
Q
What is the thickness of aluminium shield for 70Kv ?
A
1.5mm
24
Q
Why are dental x-ray tubes often set for 70kV?
A
- So that the bombarding electrons have enough energy to displace K shell electrons from the tungsten atoms
25
By what % can rectangular collimation reduce surface area irradiated by?
- 50%
26
Which of the following a drawback of using rectangular collimation?
- Increases risk of collimation errors
27
X-rays and visible light are both foth forms of EM radiation, compared to visible light, X-rays have lower:
Wave length
28
During a dental radiograph exposure, what is the primary type of interaction happening between the x-ray photons and the outer shell electrons?
- The Compton Effect
29
Which of the following is measured in Grays (Gys)
- Absorbed dose
30
What type of radiation effect are we most concerned about in dental radiography?
- Somatic non deterministic
31
What is the most common mechinism by which x-ray photons cause carcinogenisis?
- Indirect damage to DNA
32
Which of the following best decribes how an x-ray tube generates photons:
A tungsten cathode interacts with a tungsten anode to produce characterstic and continuous radation
33
What energy is required to displace K shell electrons from tungsten in an x-ray tube?
- 69.5kv
34
Which of the following is the most important piece of information when requesting a radiograph?
- The justification for taking the radiograph
35
What should focus-skin distance be for radiographs taken at 60kV or higher?
- 200mm (20cm)
36
What metal is the focusing cup in an x-ray tube made of?
- Molybdenum
37
If a person standing 2m away from an x-ray source recieves an equivalent dose of 20uSv, how many uSv will they recieve from standing 4m away?
- 5uSv
38
Based on UK averages, what is the source of roughly 50% of annual ionising radiation?
- Radon gas
39
What are the interactions occuring in the x-ray tube?
- Continuous interaction
- Characteristic interaction
40
What is continuous interaction?
- Produces continuous range of x-ray photon energies
- Bombarding e- interact with nucleus of target atom
- Max photon energy matches peak voltage
41
What is characteristic interaction?
- Produces specific energies of x-ray photon , characteristic to target element
- Bombarding e- interact with inner shell e- of target atom
- Photon energy depend on binding energies of e- shells
42
What are the two types of interaction in patient between x-ray photons and outer shell electrons?
- Photoelectric effect
- Compton effect
43
What is Photoelectric effect?
- Results in complete absorption of x-ray photon
- Involves inner shell e-
- Energy of photon must be equal to or > than binding energy of e-
- Contributes to image contrast and pt dose
44
What is the Compton effect?
- Results in scatter and partial absorption of photon (absorption lead to image formation)
- Involves outer shell e-
- Energy of incoming photon much > than binding energy of e-
- Contributes to pt dose
45
What model can we use to estimate the risk of stochastic effects?
- No threshold model
46
What is somatic non-deterministic ?
- Biological effects of radiation that are probabilistic (non-deterministic) and occur in exposed individuals body tissues (somatic)
47
What is the risk of death in panoramic radiograph?
- 1 in 1 million risk of death
48
What is the risk of death in PA radiograph?
- 1 in 10 million risk of death
49
What is the film processing common steps ?
Developing = Converts crystals to black metallic silver particles
Washing = Removes residual developer solution
Fixing = Removes non-sensitised crystals and hardens emulsion
Washing = Removes residual fixer sol
Drying = Remove water so film ready to be handled
50
What does under exposure of film lead to?
- Lighter image
51
What occurs if developer in film is too warm or too concentrated ?
- Darker image
52
What occurs if the developer solution is too old i.e past expiration date?
- Lighter image
53
What occurs if there is inadequate fixation of film?
- Contrast of image reduced
54
What occurs if film is exposed to visible light before processing?
- Darker image
55
What occurs if film appears greenish (and browns over time)
- Inadequate fixation
56
What is the main factor that affects digital radiographs?
- Exposure issues
57
What is a suitable method of viewing film images?
- On a light box
58
What are some indications of taking lateral cephalogram?
- Assess skeletal pattern
- Assess angulation of anterior teeth
- Monitor changes to above during growth/txt
- Assess antero-posterior position of unerupted teeth in anterior sextants
59
Why is collimation used in lateral cephalogram?
- Reduces radiation dose to head
60
How is the x-ray beam positioned in lateral cephalogram?
- Perpendicular to receptor and pt mid-sagittal plane
61
What is the distance between x-ray source and receptor on conventional cephalogram units?
- 1.5m+ (150cm+)
62
Why is there a large distance between x-ray sources and receptor on conventional cephalogram units?
- To reduce asymmetrical magnification of anatomy
63
During a lateral cephalogram what does the pt wear for protection and what does it protect?
- Wear lead protection
- Protects thyroid gland
64
What is the cephalostat?
- Head positioning apparatus
65
Why is the cephalostat important?
- Accuracy of image created
- Consistency (produces standardized images - useful for comparison)
- Safety to minimise amount of radiation dose to pt by using collimator to focus x-ray beam only on area of interest
- Keeps pt head still
66
What is parallax shift?
- Apparent movement of object when viewed from diff positions
- More shift occurs if objects further apart
67
What are the fundamental for parallax shift technique?
- 2 or more radiographs of object of interest
- Radiographs need ot be taken from diff angles/positions
- Shared reference point on all radiographs
- No physical movement of object and reference point between exposures
68
What pair of radiographs can't be used reliably for parallex shift technique?
- Paralleling PA and panoramic
69
What is a diagnostically acceptable image?
- No errors or minimal errors
- Sufficient image quality to answer clinical question
70
What is the target for digital and film imaging for diagnostically acceptable?
Digital = not < 95%
Film = not <90%
71
Positive of panoramic over PA radiograph?
- Capture entire dentition in one image
- Able to image non-dental areas
- Lack of I/O holder easier for gaggers, trauma, young children
72
Negatives of panoramic over PA radiograph?
- Lower spatial resolution
- More superimposition
- More artefacts
- Longer exposure time
- Higher radiation dose per image
73
What are double shadows?
- Created by structures located near centre of rotation so captured twice
- e.g soft palate and hyoid bone and cervical spine
74
What are ghost structures?
- Created by structures between x-ray source and centre of rotation
75
What are features of a ghost image?
- Appear magnified
- Blurry
- Higher due to beam inclination
- Transposed on opposite side of true anatomical position
76
What are the basic principles of ICRP system for radiation exposures?
- Justified
- Optimised (ALARP)
- Limited
77
What does IRR17 deal with?
- Occupational exposures and exposure of general public
78
What does IRMER17 deal with?
- Medical exposure of pt
79
What is the controlled area of intra-oral x-ray units?
- 1.5m from x-ray tube and within primary beam
80
What is the controlled area for cone beam CT?
- Usually entire room
- No one enter
81
What are some benefits of I/O radiographs?
- High spatial resolution
- Minimal superimposition of other anatomy
- Fast exposure
- Low radiation dose per image
82
What are some negatives of I/O radiographs?
- Limited to imaging a small area
- Invasive for pt
- Relatively difficult technique
83
What size receptor is used for anterior PA?
- Size 0
84
What size receptor is used for bitewings and posterior PA?
- Size 2
85
What size of receptor is used for occlusals?
- Size 4
86
Why is the focal trough important?
- 3D zone where structures are well-defined and sharp AKA plane of focus
- Curved area where x-ray beam focused to produce clear, well defined images
- Teeth must be positioned within focal trough so parallel to x-ray beam and film/sensor
87
In a panoramic what causes the incisors to be horixontally magnified?
- Pt too far back
88
In a panoramic what causes the posterior teeth to be horizontally magnified ?
- Pt rotated in machine
