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2ND YR- CSA- E lecs > Optimization in Radiography > Flashcards

Optimization in Radiography Flashcards

1
Q

What are the 3 principles of x ray protection?

A
  1. Justification
  2. Optimisation
  3. Limitation
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2
Q

What is optimisation?

A

Reducing the x ray dosage to a patient

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3
Q

How do we reduce the X-ray dosage patients?

A
  1. By having a selection criteria
  2. By avoiding lapses in quality assurance
  3. By avoiding unnecessary duplication of radiographs
  4. Equipment and technique factors
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4
Q

Describe the makeup fan x ray tube

A
  1. Sealed glass envelope
    2, Vacuum
    3, Anode (copper) with tungsten inset
  2. Cathode filament of tungsten wire
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5
Q

How many volts I the main supply to the x ray tube?

A

240 volts

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6
Q

What do we want to generate using th 240 volts supplied to the main xray?

A
  1. High potential difference in KV

2. A low voltage current

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7
Q

Why do we want to generate a high potential difference n an xray?

A

To accelerate electron across the xray tube

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8
Q

What do we want a low voltage current in an x ray tube?`

A

To heat the tube filament

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9
Q

How do we achieve a high potential difference?

A

A step up transformer

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10
Q

How do we achieve a low voltage current?

A

A step down transformer

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11
Q

How do we describe the 240 volts in the main x ray tube?

A

As alternating

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12
Q

What does it mean if he 240 volts in theory tube are alternating?

A

Means only half of the time is the current useful for producing x rays

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13
Q

How can we make x ray voltage more efficient?

A

1, Have a direct current unit to keep the potential constant

2. Have a shorter exposure time

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14
Q

How is having a constant potential going to make x rays more efficient?

A
  1. It keeps the kV at its peak throughout the exposure
  2. More high energy useful xray photons are produced
  3. Fewer low energy harmful X-rays produced
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15
Q

How is having a shorter exposure time going to make x rays more efficient?

A
  1. Eliminates the filament warm up time

2. Reduces dose by 0.8

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16
Q

What is the disadvantage fo reducing exposure time?

A

Contrast is also decreased

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17
Q

When are no useful X-rays being produced?

A

During the filament warm up time

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18
Q

What effect does lower doses have on the photoelectric effect?

A

The photoelectric effect predominates which is a pure absorption effect
Lower energy photons are produced which may reach the patients skin but don contribute to the final image

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19
Q

What are the regulations surrounding potential difference for intramural radiography ?

A

Tube potential can be no lower than 50 kv

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20
Q

What is the problem with reducing the Kv?

A

Contrast decreases so we do not see as many shades of grey

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21
Q

How much aluminium is added to xrays?

A

Up to 1.5mm aluminium adde for up toad including 70kV

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22
Q

What happens as filtration increases?

A

Exposure time also increases

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23
Q

What does collimation do?

A

It shapes and limits the beam size

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24
Q

How is collimation achieved?

A

By using a metal disk or cylinder

25
Q

What is the now recommend size of a collimator?

A

A rectangular shape based on the size of a size two film

(previous is used be a circular shape with a 6cm diameter

26
Q

How does changing the shape of the collimator from circular to rectangular do?

A

Can halve the dosage

27
Q

what law does th dose follow?

A

The inverse square law

28
Q

What does the intensity =

A

1/(dose)^2

29
Q

How can we reduce magnification?

A

By making the focal point to object distance to be as long as possible

30
Q

Why do want a small magnification?

A

To minimise distortion

31
Q

What is the side effect of reducing magnification?

A

We also reduce the intensity of xray this means the mA and KV have to be optimal

32
Q

What technique is used to find the optimal mA, KV and magnification

A

Spacer cone length

33
Q

What is the recommended minimum skin to focus point distance if youre operating at under 60kV

A

200mm (20cm)

34
Q

What is the recommended minimum skin to focus point distance if youre operating at over 60kV

A

100mm (10cm)

35
Q

If the cone length is decreased when using a machine at less than 60kv what is the consequence?

A

The dosage is increased

36
Q

Name the 2 different types of spacer cone shapes

A
  1. Pointer cone

2, Open ended cone

37
Q

What are the disadvantages of a pointer cone shaped spacer cone?

A

it forms a point of scatter increasing the area that is exposed radiation

38
Q

Which spacer cone shape Is recommended ?

A

Open ended cone

39
Q

Name the fastest conventional film image receptor speed that can be used intra orally

A

F speed or its equivalent

40
Q

How much faster is E speed in comparison to D speed image receptors?

A

E speed is twice as fast as D speed (so it halves the dose)

41
Q

What is the dose comparison between F speed and E speed?

A

F speed is probably 0.75 the dose of E

42
Q

Name the technique that is recommended when taking intra oral x rays

A

Film holders

43
Q

What do film holders help minimise?

A

The number of retakes tush’s reducing exposure risk to patient

44
Q

Give advantage of using film holders

A
  1. More reproducible
  2. Few repeats
  3. Projection geometry is optimal
45
Q

When taking a panoramic x ray what is recommended to be used?

A

Field trimming, sectional option wherever possible

46
Q

What are the diagnostic reference levels

A

National levels against which you can compare your own equipment

47
Q

What is the achievable dosage for inter oral radiography ?

A

1,8 mGy

48
Q

What s the diagnostic reference level for panoramic radiography?

A

66.7 mGy/mm

49
Q

How much background radiation is 2 bitewings equivalent to?

A

8-16 hrs

50
Q

How much background radiation is a panoramic equivalent to?

A

2-5days

51
Q

How much background radiation is a skull xray equivalent to?

A

40 hrs

52
Q

How much background radiation is a barium meal equivalent to?

A

15 months

53
Q

What is the risk of fatal cancer (per million) for intraoal radiographs?

A

0.02-0.6

54
Q

What is the risk of fatal cancer (per million) for an anterior maxillary occlusal radiograph?

A

0.4

55
Q

What is the risk of fatal cancer (per million) for panoramic radiographs?

A

0.21 - 1.9

56
Q

What is the risk of fatal cancer (per million) for lateral cephalometric radiographs?

A

0.34

57
Q

What is the risk of fatal cancer (per million) for cross sectional tomography radiographs?

A

1-14

58
Q

at what age is your risk of radiation poisoning highest?

A

children under the age of 10

2ND YR- CSA- E lecs (14 decks)

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