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Yr 3 - Radiology > The dental xray set, conventional image receptors and processing > Flashcards

The dental xray set, conventional image receptors and processing Flashcards

1
Q

What are the requirements of a dental X-ray set?

A

Safe and accurate

Capable of generating X-rays of appropriate kV

Small

Easy to manoeuvre and position

Stable and balanced once positioned

Easily folded and stored

Simple to operate

Robust

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2
Q

What does the tube head contain?

A

Step up transformer X-ray tube N.b. Small hole in the side to show where the X-ray tube is j side (the tungsten target)

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3
Q

What are the parts of a tube head?

A

Filament supply (cathode) Tungsten target Copper a mode Lead glass envelope

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4
Q

Which directions are X-ray beams produced in an X-ray tube?

A

All directions but lead envelope means they can only leave I’m a single direction

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5
Q

Why do we filter the X-ray beam?

A

To remove low energy photons (increase exposure but have no benefit to the image) =decrease patient dose

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6
Q

How thick should the Aluminium foil be for sets below 70kV?

A

1.5 mm

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7
Q

How thick should the aluminium foil be for X-ray sets 70kV +?

A

2.5mm

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8
Q

Why do we collimate the beam?

A

To match the beam size to the image receptor = decrease dose to patient - need to rotate to match the direction of the film - reduces dose by nearly 50% - need to be more precise when aiming to avoid cone cutting

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9
Q

What controls can be found on the control panel?

A
  • on/off switch (outside room where emitting X-rays) - timer - exposure time selection - warning lights and audible signals - exposure button
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10
Q

What are the variable factors on an X-ray set?

A

kV mA Time

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11
Q

What does and increased kV do?

A

Faster acceleration of X-rays = more penetrative = better quality - decrease patient dose - decrease contrast (more shades of gray = less absolute difference between high and low densities - increased scatter)

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12
Q

What is a dental X-ray set made up of?

A

A tube head Positioning arms Control panel and circuitry

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13
Q

What does an increased mA/time do?

A

Increased patient dose Increased film blackening (if too low = too light and over exposed)

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14
Q

What does mA/time do?

A

Determined the quantity of X-ray photons The number needed depends on the thickness of the structure you are xraying n.b. As this is very similar in dental radiographs we keep the mA the same but increase the time for molars (especially uppers)

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15
Q

What is an ac current?

A

Goes up and down (some negative) = must get rid if negative bit)

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16
Q

What is a half wave ratification?

A

Where the negative part of the wave is flipped

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17
Q

What is three wave ratification?

A
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18
Q

What is constant peak potential?

A

The wave is flipped and stays constantly at the peak

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19
Q

What are the advantages of constant peak potential?

A

X-ray production per unit time is more efficient More high energy photons per exposure Fewer low energy harmful photons are produced Shorter exposure times

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20
Q

What is the problem with old plastic pointed cones on X-ray machines?

A

They have a short- focal skin distance (fsd)

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21
Q

What is the problem with having a short focal skin distance?

A

Divergent beam = magnification of the image and a greater area is irradiated

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22
Q

How long should a cone be to be classed as long?

A

20cm

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23
Q

What is the consequence of using a long focal skin distance?

A

Beam is near parallel = minimal magnification and less area irradiated

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24
Q

What are the two types of conventional image receptors?

A

Direct action film Indirect action film

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25
Q

What is a direct action film?

A

The X-ray photons interact with the film

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26
Q

What is an indirect action film?

A

The X-ray photons interact with an intensifying screen producing light which interacts with the film

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27
Q

What does the packaging of a direct film look like?

A

Front of the film is white and back is coloured depending on the type of X-ray film in use

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28
Q

Which size film do you use for: Posterior teeth Anterior teeth Occlusals

A

Posterior teeth = size 2 Anterior teeth = size 0 or 1 Occlusal teeth = size 4

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29
Q

What are the components inside the film packet of a direct film?

A

Black paper Film Lead foil Moisture resistant outer cover

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30
Q

What is the black paper used for?

A

Protective layer (the emulsion is easily scratched/damaged)

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31
Q

What is the purpose of the lead foil?

A

When X-ray passes through it can cause scatter and bounce back off of other structures in the mouth = the lead reduces the exposure from the rest of the mouth but does not stop everything

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32
Q

What are the layers in cross section of a film?

A

Protective layer Emulsion Adhesive Transparent plastic base (blue tinted) Adhesive Emulsion Protective coating

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33
Q

What is emulsion?

A

The active layer 90% = silver halide crystals in gelatin matrix 10% = silver iodo-bromide

34
Q

What does the iodobromide in the emulsion do?

A

Increases sensitivity

35
Q

What effect do X-rays have on the silver halide crystals?

A

They sensitise the crystals they strike = latent image (sensitised crystals are reduced ti black metallic silver in the developer)

36
Q

What is film speed?

A

The exposure required to produce an optical density of 1.0 above background fog (Faster film= less exposure required = less dose to patient because need less X-rays to produce blackening) Slowest –> fastest D -> E -> F -> Digital

37
Q

What is the problem with higher film speed?

A

Film speed is a function of the number and size of silver halide crystals in the emulsion -> the larger the crystals the faster (less dose) BUT there is some loss of image quality N.b. Doesn’t apply to digital

38
Q

So which film speed should we use?

A

The fastest film consistent its adequate diagnostic results = for intraoral = f speed

39
Q

Which layers do indirect action cassettes contain?

A

Intensifying screen that absorbs low energy photons Film Intensifying screen that absorbs high energy photons

40
Q

What casing surrounds an indirect cassette?

A

Light tight aluminium/ carbon fibre casing

41
Q

What is the advantage of indirect action films?

A

Images much thicker parts of the body (intensifies electrons)

42
Q

What are intensifying screens?

A

= fluorescent phosphors embedded in a plastic matrix which emit light when excited by X-rays - one X-ray photon produces many light photons (fewer X-ray photons required to produce an image = decreases patient dose but at expense of image resolution = not as sharp)

43
Q

How do we measure resolution?

A

Line pairs per mm Resolution = the ability to differentiate between different structures that are close together on the radiograph

44
Q

What is the resolution for direct action films?

A

Approx 10 line pairs per mm

45
Q

What is the resolution for indirect action films?

A

Approx 5 line pairs per mm

46
Q

How do we calculate intensification factor?

A

= exposure required when screens not used / exposure required with screens

47
Q

What are rare earth screen components?

A

Terbium = activated screens emit green light Thulium = activated screens emit blue light Yttrium = activated screens emit ultraviolet light N.b films must be matched to the screens

48
Q

What are the benefits of rare earth screens over calcium tungstate screens?

A

5 X faster than calcium tungstate = lower dose to patient

49
Q

Which conditions must film processing be performed under?

A

Controlled, standardised conditions with attention to detail (temp, time, keeping chemicals up to strength

50
Q

What is a common cause of film faults?

A

Poor processing (poor quality radiographs = need repeating)

51
Q

What is film processing?

A

The process by which we convert the invisible latent image into visible radiographs

52
Q

What are the advantages of automatic processing over manual processing?

A

Time saving (5 mins rather than 20) No darkroom required Controlled standardised processing conditions Automatic replenishment if chemicals

53
Q

What are the 5 stages of film processing?

A
  1. Development 2. Clearing & 3. Fixation 4. Washing 5. During
54
Q

What happens in the development stage?

A

Sensitised halide crystals in emulsion are converted to black metallic silver IMPORTANT = needs correct conc of solution, time and temp

55
Q

What happens if the development solution is too strong, long or hot?

A

Over developed film (film too dark)

56
Q

What happens if development solution is too weak, short or cold?

A

Film is underdeveloped (film too pale)

57
Q

What is the developing solution?

A

Alkaline pH 10.5 Oxidised by air over time (becomes less effective) = should be changed approx every 14 days but this depends on how often it is used

58
Q

What happens in the fixation stage?

A

Unsensitised silver halide ions in emulsion are removed to reveal transparent/ white parts of image Emulsion is hardened (fixer firmly anchors the silver grains onto the film base)

59
Q

What is the fixing solution?

A

Acidic pH 4-4.5

60
Q

What are the timings needed for clearing and then fixing?

A

Clearing time = time taken to remove unsensitised crystals Fixing time = usually 2x clearing time = not as critical as developing = approx 8-10 mins for manual processing

61
Q

What does an under fixed film look like?

A

Greenish yellow/ milky = may discolour to brown over time

62
Q

What happens in the washing stage?

A

The film is washed thoroughly to remove any residual fixer (any remaining on film will stain brown) N.b. If manual processing also wash film briefly between development and fixation to remove any residual developer

63
Q

Which other film faults can you get from processing?

A

Chemical splashes (fixer splashes prior to development or developer splashes) Films stuck together Light fogging Marks from dirty rollers

64
Q

What do white splashes show?

A

Fixer has been splashed prior to development (Mainly an issue in manual when fixer is splashed on packets waiting to go into developer)

65
Q

What do brown splashes show?

A

Developer splashes

66
Q

How long must you leave between inserting each film packet in an automatic developer?

A

10 seconds

67
Q

What is light fogging?

A

When film is exposed to daylight

68
Q

What causes marks from dirty rollers?

A

Failure of housekeeping = build up of chemicals

69
Q

What is at fault in this film?

A

Developer splashes

70
Q

What is wrong with these films?

A

Stuck together (didnt leave enough time before feeding next one in)

71
Q

What is wrong with this film?

A

Light fogging

72
Q

What is wrong from this film?

A

Marks from dirty rollers

73
Q

What does the cross section of an xray film look like?

A
74
Q

What is wrong with this film?

A

Overdeveloped

75
Q

What is wrong with this film?

A

Underdeveloped

76
Q

Whatn is wrong with this film?

A

Fixer splashes prior to development

77
Q

What does the inside of a film packet look like?

A
78
Q

What is wrong with this film?

A

Overexposed

79
Q

What is inside an xray tube?

A
80
Q

What are the compents of a dental xray head, tube and cone?

A

Yr 3 - Radiology (9 decks)

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