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Foundations of clinical skills > How do you create an x-ray image? > Flashcards

How do you create an x-ray image? Flashcards

1
Q

What are the 2 types of radiographic film?

A

Direct action film

Indirect action film

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2
Q

What film would be described as ‘direct action’?

A

Wrapped or packet film for intra-oral radiography

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3
Q

What film would be classed as ‘indirect action’?

A

Used in conjunction with intensifying screens inside an extra oral cassette

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4
Q

What size film are routinely used for anterior PA radiographs and children’s bitewings?

Are these direct or indirect action films?

A

22 x 35mm

Direct

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5
Q

What size film are routinely used for posterior PA radiographs and adult bitewings?

Are these direct or indirect action films?

A

31 x 41mm

Direct

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6
Q

What size film are routinely used for occlusal radiographs?

Are these direct or indirect action films?

A

57 x 76 mm

direct

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7
Q

Why should films be packaged in plastic barrier envelopes?

A

For the purposes of infection control

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8
Q

Name the 3 types of film speeds

A

D
E
F

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9
Q

How are different speed films packaged in order to be able to differentiate between them?

A

They use different colours to tell them apart (but no consistency with colours chosen between manufacturers)

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10
Q

In what ways are the film packets often very similar irrespective of the manufacturer or speed?

A

Clear plastic barrier envelope
Outer plastic wrapper (white & colour coded)
Plastic film with embossed dot in one corner (orientation- when viewing radiograph raised dot points towards operator)

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11
Q

What is inside a film packet?

A

Black paper
Film itself (emulsion)
Lead foil sheet

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12
Q

Describe the packet contents of an intra-oral radiographic film packet (5)

A
  • Clear plastic barrier envelope (ideally)
  • Outer wrapper - white/colour coded
  • Plastic film with embossed dot - on one corner
  • Black paper either side of film
  • thin sheet of lead foil
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13
Q

Outline the order of the film base and emulsion in an intra oral radiographic film (7)

A
  1. Protective layer (gelatin)
  2. Emulsion (silver halide - appears green)
  3. Adhesive
  4. Plastic base
  5. Adhesive
  6. Emulsion (silver halide)
  7. Protective layer (gelatin)
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14
Q

Why is the lead foil inside the film packet often embossed with a pattern?

A

Because this allows easy identification of the error of placing the film packet the wrong way round

(The resultant film will be pale and will show pattern of the foil)

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15
Q

What are the functions of the lead foil?

A
  1. Prevents same residual radiation passing on into patient
  2. Prevent some scattered photons from coming backwards (that have hit patient’s tissues) and hitting the film (which would degrade the image)
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16
Q

How does an instant process or self-developing film work?

A
  • Film is packaged in a plastic sachet which contains packets of both fixer and developer solutions
  • The film is exposed - the developer tab is pulled and the solution moves down through the plastic sachet to the film
  • After ~15 seconds the fixer tab is pulled, which allows it to contact the film
  • The chemicals are then discarded and the film is washed in water
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17
Q

Do the instant process/self developing films require dark room or processing facilities?

A

No

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18
Q

Why are the results poor from self-developing films?

A

They are poor in terms of image quality and there is no protective lead foil in the packet

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19
Q

When may self-developing films be useful?

A

May be useful in emergency situations, where dark room facilities are not available but they should not be used routinely

e.g. may be useful in specific essential situations such as during surgery or endodontics

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20
Q

What speed film should be used in line with current recommendations (2001 guidance notes)?

A

E or F speed

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21
Q

What is used in conjunction with indirect action film?

A

2 intensifying screens (one in front, one behind) inside container/cassette

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22
Q

What is the silver halide emulsion on an extra-oral indirect film designed to be primarily sensitive to?

A

Designed to be sensitive to various colours of light - NOT x-rays.

(Unlike intra-oral which are designed to be sensitive to x-rays)

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23
Q

Why are intensifying screens needed with indirect action films?

A

Because they emit the correct light colour

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24
Q

How can you tell if an extra-oral radiograph is the right way round?

A

There are right and left metal letters on outside of the cassette

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25
Q

What are the white intensifying screens used in indirect action radiographs made from?

A

They are made of fluorescent phosphors embedded in a plastic matrix

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26
Q

What happens to the phosphor within the intensifying screens when they are hit by x-rays?

A

They emit light

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27
Q

Name 2 examples of phosphor in intensifying screens

A

Calcium tungstate
Gadolinium
Lanthanum
Yitrium

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28
Q

Different screens emit different colours of light - what colours are typically emitted? (4)

What colour light do most modern screens emit?

A

Blue, green, UV or red light

Most modern screens emit green light

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29
Q

What will happen to the resulting image if close contact between the screens and film isn’t maintained?

A

The image will be blurred

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30
Q

Describe the action of conventional calcium tungstate screens that emit blue light (4)

A
  1. Incoming x-ray photon activates the phosphor which emits light
  2. The light diverges and hits the film emulsion
  3. It crosses over through the clear film base and hits the film emulsion on the other side
  4. Those photons that pass through and hit the rear screen have the reverse effect
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31
Q

Describe the action of an ultraviolet system of intensifying screens and why the resulting image may have better resolution/be sharper

A
  1. Incoming photon activates phosphor, but has little crossover effect through film base

This is why the image will have sharper edge definition or resolution

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32
Q

What is the reason for using film-based image receptor with intensifying screens, rather than a film on its own?

A

Because a reduced overall number of x-ray photons are needed to produce enough visible light to create an image - thus reducing the dose to the patient

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33
Q

What is the mechanism for light emission from intensifying screens (same applies for both calcium tungstate/blue light and rare earth/green light screens) (3)

A

X-ray photons enter
They hit the intensifying screen - this creates light (blue or green)
The light then diverges and hits the film

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34
Q

What would happen if there was a gap between the intensifying screens and the film?

A

The light will diverge more before hitting the film so a larger area of film is affected and the image will be less sharp and more blurred

35
Q

What is the advantage of using rare earth films instead of calcium tungstate films?

A

The initial amount of x-rays required to generate the light is considerably less than calcium tungstate - so the dose to the patient can be reduced further

36
Q

Why must intensifying screens be looked after and made sure to be clean etc?

A

Any dirt or marks on the screens will prevent the emitted light from hitting the film.

They also require careful handling to avoid scratches or damage

37
Q

Describe the construction of the cassette

A

The film is sandwiched tightly between the front and back intensifying screens.
Beyond the intensifying screens there is a layer of sponge rubber which helps compress the cassette together
The cassettes typically consist of a light-tight aluminium or carbon fibre box

38
Q

Ideally what type of screen should be used?

A

Rare earth intensifying screens

39
Q

In what way must you make sure that the film matches the intensifying screens?

A

You must make sure that the light colour sensitivity of the film should match the colour of light emitted from the screens

40
Q

What is determined by kilo voltage?

A

It determines the energy of the photons or quality of the beam produced.
Which in turn determines the penetrating power of the photons which affects the film contrast

41
Q

What is meant by contrast?

A

The visual difference between black and white

42
Q

What happens as kilo voltage is increased?

A

The visual difference between black and white becomes less obvious - instead there are multiple shades of grey

43
Q

What happens as kilo voltage is decreased?

A

The image becomes black and white

44
Q

What 2 factors determine the quantity of x-ray photons which are used?

What affect does this have on the film?

A

The mA (milliamperage) and time

This affects the degree of film blackening
If a conventional film is:
> over-exposed it will appear too black
> under exposed it will appear pale

45
Q

What is meant by the term ‘chemical processing’?

A

It describes the events required to convert the so-called invisible latent image within the emulsion into the visible black, white and grey radiographic image

46
Q

What was the name of the technique used traditionally to process radiographic films?

A

This manual process was called wet processing

where the film was clipped onto metal film holder and then immersed into tanks of chemicals

47
Q

What is sensitised when a film has been exposed?

A

The silver bromide emulsion is sensitised

48
Q

What is the action of the developer - what does it do to the silver bromide?
What colour is the unexposed part of a film?

A

It causes the sensitised silver bromide to be reduced to black metallic silver.

The unexposed part of a film remains green

49
Q

What is the action of the fixer on the silver bromide emulsion on the film?

A

It ensures that the residual green silver bromide emulsion is removed to reveal the clear or white base underneath

50
Q

Is the developer solution acid or alkaline?

A

alkaline

51
Q

Why does the effectiveness of the developer solution decrease over time?

A

Because it is oxidised by air

So the ability of the developer to blacken a film should be monitored regularly

52
Q

What 2 factors is the development process dependent on?

A

It is time and temperature dependent

53
Q

How long and at what temperature is used to manually process a film?

A

5 minutes at 20 degrees Celsius

54
Q

Will over developed films appear too dark or too pale?

and vice versa for under developed films

A

They will appear too dark

55
Q

Is the fixing solution acid or alkaline?

A

Acid

56
Q

What may films look like if they have been inadequately fixed?

A

They may look greenish-yellow or milky as a result of residual emulsion being left behind

They may become brown with time

57
Q

How long should films ideally be fixed for compared to the clearing time?

A

They should ideally be fixed for twice the clearing ime

58
Q

What are the current recommendations for chemical processing from the 2001 Guidance Booklet? (3)

A
  1. Strict quality assurance procedures should be applied
  2. Processing facilities should be properly cleaned, maintained and operated at the correct temperature
  3. The developer solution should be changed at regular intervals as recommended by the manufacturer
59
Q

What are the 2 main types of digital image receptors?

A

Intra and extra-oral solid-state receptors
Intra and extra-oral phosphor plate receptors

(both create very similar digital images)

60
Q

What is an alternative name for solid-state systems and why ?

A

Real time digital imaging

Because of how quickly they produce an image

61
Q

What sensors can be used in solid-state systems?

A

CCD (charge couple device) sensors
CMOS (complementary metal oxide semiconductor) sensors

These sensors are connected directly to the computer with the big advantage of almost instantly producing an image on the computer screen
Disadvantage: intra-oral sensors quite bulky and can be difficult to position accurately

62
Q

What is a solid-state intra-oral sensor made from?

A

it consists of an array of CCD pixels and above these, there is a scintillation layer that fluoresces when hit by x-ray photons
Each individual pixel consists of a sandwich of N- and P-type silicon

63
Q

How does an intra-oral CCD sensor work? (5)

A

The x-ray photons pass through patient and hit phosphor scintillation layer which acts like an intensifying screen by photoelectric effect and emits light.

The light interacts with the silicon in each of the CCDs to create a charge packet which is concentrated by the electrodes and converted to an analogue voltage

This analogue voltage then passes down the cable and into the computer’s analogue-to-digital converter - which changes it into a digital signal

Each pixel is measured and given a numerical score from 0-255

Each numerical value is converted to a grey scale from black through to white

64
Q

What is an alternative way to produce digital images aside from the solid-state system?

A

The phosphor plate/cordless systems

They are not connected directly to a computer so the image is NOT instantaneous (a second stage is required)

65
Q

What is the second stage of cordless systems?

What is a clinical advantage of this system?

A

It involves a reader in which a laser beam is used to scan the plate and create the image

Adv: plates are as easy to use as conventional film packets
Disadv: more time consuming

66
Q

How long does it usually take for a phosphor plate to get scanned in the machine and how is it cleared in this machine?

A

It is scanned in about 7 seconds

It is automatically cleared using white light

67
Q

Describe how phosphor plate systems work (8)

A
  1. The plates consist of a layer of barium fluorohalide phosphor on a backing plate - x-rays pass through the patient and hit the phosphor layer
  2. Instead of light being emitted immediately (like conventional intensifying screens), the x-ray energy is stored in the storage phosphor plate
  3. The plate is placed into the reader
  4. Laser beam is shone onto the plate, which releases the stored x-ray energy as green light
  5. The green light is picked up in the reader by a photo-multiplier tube which converts the light into a voltage
  6. Gradually, the laser beam travels down the plate - releasing the energy contained throughout the plate in the form of green light. Eventually releasing all the energy contained in the plate
  7. The various voltages are then passed into the computer’s analogue-to-digital converter, which creates a discrete digital numerical signal
  8. The image is divided up into little pixels and each pixel is allocated a number from 0-255 which is displayed back as a black, white and grey image
68
Q

How many shades of grey are in involved in a digital radiograph?

A

256 shades of grey

Each pixel is assigned a shade of grey depending on the amount of radiation that has reached that part of the sensor

69
Q

Is the resulting image more likely to be an accurate representation if smaller or larger sensor pixels are used?

A

Smaller sensor pixels

70
Q

How are digital images measured?

A

Measured by the size of pixels

71
Q

What size are pixels for storage phosphor plates?

A

60-70 microns

72
Q

What size are the pixels used for CCD?

A

20-70 microns

Theoretically, CCD resolution should be better than phosphor plates

73
Q

What is spatial resolution?

A

It is when resolution is measured in line pairs/mm.

It is an indication of how many line pairs can be seen in a millimetre.
The more line pairs that can be seen, the better the resolution.
This also allows analogue and digital and image receptors to be compared.

74
Q

What is the spatial resolution of intra-oral direct action packet film?

A

10-20 lp/mm depending on film speed

75
Q

What is the spatial resolution of indirect-action film/intensifying screen combinations?

A

It is in the order of 5 lp/mm

2 stage process - so visible loss of image sharpness

76
Q

What is the spatial resolution of digital systems?

A

It varies between 7 and 25 lp/mm

This resolution is therefore superior to film-screen combinations and comparable to or better than direct action film packet film

77
Q

Why is digital imaging sometimes referred to as image processing or image enhancement?

A

Because it does not involve chemicals and is done using computer software

78
Q

What can be altered using digital enhancement on a digital radiograph?

A

Brightness
Contrast
Can invert the image - make black white and white black
Image can be embossed to create pseudo 3D image
Pseudo colours can be used

79
Q

What is the significance of being able to alter the contrast of a digital radiograph?

A

It makes the role of kilovoltage in controlling and affecting contrast of film-captured images irrelevant

80
Q

What is one of the issues with copies of digital radiographs?

A

It is difficult to print/produce hard copies of digital radiographs.
Printer usually will not reproduce the 256 shades of grey.
Quality of image is never as good as quality on a monitor.

Other printers are available that could improve the image quality but these are very expensive.

81
Q

What are the advantages of digital imaging? (6)

A
  • Lower radiation dose (esp using solid-state sensors)
  • Eliminates chemical film processing
  • Images acquired rapidly
  • Images can be altered/manipulated using image processing independent of exposure factors that have been used
  • Images can be electronically stored and archived - films not lost
  • Digital images can be easily shown and explained to patients
82
Q

What are the disadvantages of digital imaging? (6)

A
  • Systems are expensive
  • Require large electronic storage capacity
  • Solid state sensors are bulky and can be difficult to use clinically and can be easily damaged
  • Image manipulation if person isn’t aware of what they are doing and how they are changing the image - evidence of disease may be inadvertently lost
  • Hard copies often poor quality
  • Computers can crash and clinical info can be lost (backing up is essential)
83
Q

What are the current recommendations from the Guidance Notes Booklet 2001 regarding digital imaging? (3)

A
  • Intra-oral sensor sizes should be available in a range that is comparable to dental film
  • Sensitivity of detector system should be compatible with x-ray set being used, and ideally should be DC or constant potential unit (allows for short exposure times).
  • Ensure retakes are properly justified, recorded and included in quality assurance stats. Due to the ease with which radiographs can be retaken.

Foundations of clinical skills (9 decks)

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