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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
What is the now recommend size of a collimator?
A rectangular shape based on the size of a size two film | (previous is used be a circular shape with a 6cm diameter
26
How does changing the shape of the collimator from circular to rectangular do?
Can halve the dosage
27
what law does th dose follow?
The inverse square law
28
What does the intensity =
1/(dose)^2
29
How can we reduce magnification?
By making the focal point to object distance to be as long as possible
30
Why do want a small magnification?
To minimise distortion
31
What is the side effect of reducing magnification?
We also reduce the intensity of xray this means the mA and KV have to be optimal
32
What technique is used to find the optimal mA, KV and magnification
Spacer cone length
33
What is the recommended minimum skin to focus point distance if youre operating at under 60kV
200mm (20cm)
34
What is the recommended minimum skin to focus point distance if youre operating at over 60kV
100mm (10cm)
35
If the cone length is decreased when using a machine at less than 60kv what is the consequence?
The dosage is increased
36
Name the 2 different types of spacer cone shapes
1. Pointer cone | 2, Open ended cone
37
What are the disadvantages of a pointer cone shaped spacer cone?
it forms a point of scatter increasing the area that is exposed radiation
38
Which spacer cone shape Is recommended ?
Open ended cone
39
Name the fastest conventional film image receptor speed that can be used intra orally
F speed or its equivalent
40
How much faster is E speed in comparison to D speed image receptors?
E speed is twice as fast as D speed (so it halves the dose)
41
What is the dose comparison between F speed and E speed?
F speed is probably 0.75 the dose of E
42
Name the technique that is recommended when taking intra oral x rays
Film holders
43
What do film holders help minimise?
The number of retakes tush's reducing exposure risk to patient
44
Give advantage of using film holders
1. More reproducible 2. Few repeats 3. Projection geometry is optimal
45
When taking a panoramic x ray what is recommended to be used?
Field trimming, sectional option wherever possible
46
What are the diagnostic reference levels
National levels against which you can compare your own equipment
47
What is the achievable dosage for inter oral radiography ?
1,8 mGy
48
What s the diagnostic reference level for panoramic radiography?
66.7 mGy/mm
49
How much background radiation is 2 bitewings equivalent to?
8-16 hrs
50
How much background radiation is a panoramic equivalent to?
2-5days
51
How much background radiation is a skull xray equivalent to?
40 hrs
52
How much background radiation is a barium meal equivalent to?
15 months
53
What is the risk of fatal cancer (per million) for intraoal radiographs?
0.02-0.6
54
What is the risk of fatal cancer (per million) for an anterior maxillary occlusal radiograph?
0.4
55
What is the risk of fatal cancer (per million) for panoramic radiographs?
0.21 - 1.9
56
What is the risk of fatal cancer (per million) for lateral cephalometric radiographs?
0.34
57
What is the risk of fatal cancer (per million) for cross sectional tomography radiographs?
1-14
58
at what age is your risk of radiation poisoning highest?
children under the age of 10

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

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