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Clinical Dental Science BDS3 > Radiology > Flashcards

Radiology Flashcards

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1
Q

How can X-rays on a graph be systematically shown?

A

As a sine wave

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2
Q

What is the speed of light?

A

3x10(8)ms-1

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3
Q

What is the name of the innermost electron shell?

A

The K shell

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4
Q

What is the name of the energy that must be exceeded in order to remove an electron from its shell

A

The binding energy must be exceeded

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5
Q

Which electron shell has the highest binding energy

A

The closer the electron is to the nucleas the higher the binding energy - K has the highest binding energy

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6
Q

How can you work out the specific amount of energy required to move an electron to an outer shell

A

The energy required to move an electron to an outer shell is the difference in the binding energey of the shells

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7
Q

What kind of current does X-ray production require?

A

X-ray production requires a unidirectional current

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8
Q

X-ray production requires a uni-directional current but xray units are powered by alternating current. The units have a generator to modify this so that it mimics a direct current.
What is this change called?

A

Refraction

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9
Q

Does divergence decrease or increase with distance from the xray source?

A

Divergence decreases with the distance from the xray source

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10
Q

What is the inverse square law

A

Intensity beam is inversely proportional to the square of the distance between the xray source and the point of measurement

Therefore if you DOUBLE the distance you will quarter the dose

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11
Q

What is the purpose of the glass envelope in the xray tube

A

The glass component acts as a vacuum to ensure the electrons are not hindered by gas molecules

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12
Q

Why does the metal sheielding tend to be made of lead

A

This absorbs the X-rays

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13
Q

What sis the purpose of the aluminium filtration?

A

This removes the lower energy, non diagnostic X-rays from the Bea,

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14
Q

What is the purpose of the oil in the xray tube head

A

This dissipates the heat produced by the xray tube by thermal convection

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15
Q

The spacer cone provides the ‘focus to skin distance’’ what is this distance?

A

200mm

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16
Q

What is the purpose of the collimator

A

This is a lead diaphragm attached to the end of the spacer cone and this acts too reduce the patient dose

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17
Q

What is the benefit of rectangular collimation

A

It can potentially reduce surface area irradiated by almost 50%
It can also improve image contrast by reducing scatter

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18
Q

What is the penumbra affect and why one’s it happen?

A

This is blurring of the radiogrpahic image due to the focal spot not being a single point but rather a small area

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19
Q

How can the penumbra affect be reduced

A

This can be minimised by shrinking the focal spot

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20
Q

What are the three fates of X-ray photons emitted from the focal spot.

A
  1. Attenuated by the lead sheilding
  2. Attenuated by the aluminium filtration
  3. Exit tube-head to form the x-ray beam
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21
Q

Describe continuous radiation

A

Bombarding electrons interacts with the nucleas of the target atom, causing the electrons to be rapidly decelerated and deflected - kinetic energy released as xray photons.

Produces a continuous range of xray photon energies

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22
Q

Describe characteristic radiation

A

Bombarding electrons interact with inner electron shells target atom, photon energies depend on the binding energies of the electron shells

Produces specific energies of xray photon, characteristic to the element used for that target

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23
Q

What does it mean if an electron has been ionised

A

It has been displaced entirely

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24
Q

What does it mean if an electron has become excited

A

It has moved to an upper shell

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25
Q

Scattered and absorbed electrons cause reduction in the intensity of the ray beam, what is the term for this?

A

Attenuation

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26
Q

What are the three ways photons in a diagnostic xray can interact with matter

A

Transmission - pass though unaltered
Absorption - stopped by the matter - so fully deposited into the tissues
Scatter - changes direction

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27
Q

Attenuation indirectly leads to the radiographic image because diffferent tissues have varying degrees of attenuation, what level of attenuation do the three colours represent;
Black, grey and white

A

Black - minimal attentution
Grey - partial attenuation
White - complete attenuation

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28
Q

What is the photoelectric effect

A

Photon in xray beam interacts with the INNER SHELL electron in subject, resulting in absorption of the photon and creation of photoelectron.

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29
Q

When does the photoelectric affect occur

A

This occurs when the energy of the incoming photon is equal to ( or just greater than) the binding energy of the inner shell electron

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30
Q

With what kind of electrons does the photoelectric effect predominate with

A

Lower energy photons

Since human tissues have relatively low binding energies

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31
Q

What is the Compton effect

A

Photon in xray beam interacts with OUTER SHELL electrons,resulting in partial absorption and scatter of the photon and creates a recoil electron

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32
Q

When does the Compton effect occur?

A

Occurs when energy of the incoming photon is MUCH greater than the binding energy of electron

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33
Q

What kind of electrons predominate in the Compton effect

A

Much higher energy photons and shell electrons which are loosely boud

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34
Q

What direction do lower energy photons tend to scatter in and does this affect the image

A

Lower energy photons tend to ‘backward scatter’ and they do not affect the image

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35
Q

Higher energy photons tend to undergo forward scatter these may still reach the receptor, what are the issues with this?

A

Can cause darkening of the images in the wrong places
Results in ‘fogging’ of image - reduces image contrast/ quality

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36
Q

What kind of scatter is mainly found on an xray tube operating at 70kV

A

Forward scatter, forward scatter is the reason the control area need too completely surround the patient

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37
Q

How can we reduce scatter?

A

Collimation; reducing the size and shape of the beam

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38
Q

What is the problem with lowering Kv on the xray unit

A

This increases the dose absorbed by the patient

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39
Q

What is the effect of raising kV on xray unit

A

It results in reduced contrast between the tissues with different Z so resulting in rubbish images

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40
Q

What is the differences; name 3; between ( continuous radiation and characteristic radiation interaction) and ( photo electric and components effect)

A

Continuous and characteristic radiation
- occur in xray tube
- electrons interacting with tungsten atoms
- leads to production of xray photons

Photoelectric and Compton
- occurs in patient/receptor/sheilding
- xray photos interact with atoms
- leads to attenuation of xray beam

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41
Q

Each ionisation process will deposit a certain amount of energy locally, what approximate amount?

A

35eV`

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42
Q

What is the most significant effect of ionising radiation

A

Damage to DNA

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43
Q

What damage can happen to the DNA when exposed to Ionsing radiation?

A

Faulty repair of chromosome breaks

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44
Q

Describe the direct effect of radiation on DNA

A

Radiation interacts with the atoms of a DNA molecule or another important part of the cell

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45
Q

What is the indirect effect of radiation on DNA

A

Radiation interacts with water in the cell, producing freee radials which can cause damage

Free radicals are unstable, highly reactive molecules

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46
Q

What type of break in DNA can usually be repaired

A

Single strand break can usually be repaired

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47
Q

Double stranded breaks are usually more diffult to repair, what kind of radiation usually causes these?

A

Alpha radiation

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48
Q

What is the problem with double stranded DNA breaks

A

If their repair is faulty this can lead to mutations which can affect cell function e.g. if they are mis-rejoined

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49
Q

What two factors is tissue radio-sensitivity dependant on?

A

The function of the cellls that make up the tissues
If the cells are actively dividing

50
Q

The more rapidly the cell is dividing, the greater the sensitivity to radiation.

Name 3 highly radio- senstive cells

A

Bone marrow, lymphoid tissue, gastrointestinal tissue

51
Q

What is absorbed dose

A

The energy deposited by the radiation

52
Q

What is equivalent dose

A

Equivalent dose is the absorbed dose multipled by a radiation weighting factor

53
Q

What is effective dose

A

Equivalent dose to each organ, multipled by the tissue weighting factor

54
Q

What does the LNT model do?

A

Estimates the long term biological damage from radiation

55
Q

There are two biological effects that radiation can have.
Name both;

A

Deterministic effects

Stochastic effect

56
Q

What is the deterministic effect of radiation

A

Tissue reactions.
They only occur above a certain dose
The severity of the effect is related to the dose recieved

57
Q

What is the stochastic effect of radiation

A

This is the basis of the LNT model
The probability of the occurrence is related to the dose recived

58
Q

What are the two categories of stochastic effects

A

Somatic - results in a disease of disorder e..g cance
Genetics - abnormalities in descendants

59
Q

Does pregnancy need to be taken into account when taking a dental X-ray, explain your answer

A

Pregnancy des not need to be taken into account for dental X-rays because the dose to the foetus is so low.

The foetus should not be irradiated inadvertently nor should the X-ray bema be directed at the patients abdomen

60
Q

What is the estimated annual background radiation dose

A

2,2mSv

61
Q

What does comes form an intra-oral X-ray

A

0.005mSv

62
Q

Who does the IRMER17 guidance apply to.

A

Patients

63
Q

IRR17 guidance applies to who

A

Staff and the public

64
Q

How far should be control area extend from the X-ray tube and patient?

A

At least 1.5m

65
Q

Radiation protection philosophy is
Justification
Optimisation
Dose limitation

What do these mean

A

Justification - practices must have sufficient benefit to individuals or society in order to offset detriment

Optimisation - indictable doses and the number of people exposed should be kept as low as reasonably practicable, taking into account economic and social factors

Dose limitation - system of individual dose limits so that the risks to Individuals are acceptable

66
Q

What does ALARP mean and what does this refer to

A

As low as reasonably practicable

This refers to the protection of patients dose - dose optimisation

67
Q

What are diagnostic reference levels and what are they used for?

A

Legislation requires employers to have established dose levels for typical examinations for standard size patients.

They are compared to national reference levels and enables identification of units giving a high r dose

68
Q

What is the plate and sensor used in digital radiography?

A

Phosphor plate and solid state sensor

69
Q

There are three types of phosphor plate sizes, 0 2 and 4. Name what kind of radiograph each is usually for.

A

0 - anteior periapicals
2- bitewings and posterior peripapicals
4- occlusal radiographs

70
Q

What effect does having more pixels on a radiographic image have

A

More pixels=better detail= higher resolution

71
Q

Radiographs are typically processed in how many bits and how may gray shades are available

A

8 bits

256 gray shades

72
Q

What is the international standard format for handling digital medical image called

A

DICOM

Digital imaging and communications in medicine

73
Q

PACS is a medical imaging technology which provides storage and access to images

What does PACS stand for

A

Picture archiving and communication system

74
Q

What are the two types of digital intra-oral receptor?

A

Solid state sensor
Phosphor plate

75
Q

How is the final image created in a phosphor plate

A

This plate is not connected to the computer, after it has been exposed to the x-rays it must be put into a scanner and read to create the final image

76
Q

How is the image produced from the phosphor plates in the scanner

A

The receptor is scanned by a laser and the laser energy causes the excited phosphor crystals to emit visible light.
This light is dectected and creates the digital image `

77
Q

Solis state sensors are connected to the computer and the final image is created virtually and instantly. Why are these not as commonly used

A

They are more bulky and more expensive

78
Q

What is the purpose of the identification dot on the receptor

A

To aid orientation of the image

79
Q

Name 3 advantages of phosphor plates versus solid state sensors

A

Thinner lighter and usually flexible
They are wireless
More comfortable for the patient

80
Q

What is the purpose of silver halide crystal n film radiography

A

They are embedded in the gelatin binder and they effectively become the ‘pixels’ in the final image

They become sensitised upon interaction with x-ray photons and then during processing they sensitised crystals are converted to particles of black metallic silver which are the dark parts of the image.
Non sensitised crystals are removed - lighter parts of the image

81
Q

If a film radiograph had been taken are there was an embossed pattern showing upp on the image, what has happened here?

A

This is the lead foil showing and the receptor has been placed the wrong way round

82
Q

If you increase the film speed will that cause an increase or decrease in the amount of radiation required to achieve an image?

A

Reduction

83
Q

Film speed is affected by the number and size of silver halide crystals.

If you have larger crystals what will this result in?

A

Larger crystals will result in a faster film but a poorer image quality

84
Q

In regards to film speed receptor E is twice as fast as receptor D, what does this mean in terms of radiation dose and exposure time with E compared to D

A

E needs half the exposure time and half the radiation dose

85
Q

What percentage is the reduction dose when you change from E receptor to F

A

20

86
Q

Intensifying screens are used along indirect action fil for extra-oral radiographs, they reduce radiation dose but what is the consequence of them?

A

They Also reduce detail

87
Q

What are the 5 steps in film processing?

A
  1. Developing
  2. Washing
    3.fixing
    4.washing
  3. Drying
88
Q

Why is the manual cycle done in a red light room

A

Because the red light doesn’t interact with the radiogrpahic emulsion

89
Q

Name 2 advantages and 2 disadvantages of self developing films

A

Advantages
- no darkroom or processing facilitates required
- faster

Disadvantages
- poorer image quality
- image deteriorates more rapidly over time

90
Q

What three things can the developing process of film radiographs be affected by

A

Time, temperature and solution concentration

91
Q

What are three developing issues which could cause the radiograph to come out pael

A

Film removed from the solution too early
Solution too cold
Solution too. Old/dilute

92
Q

Radiographic image looks greenish and becomes brown over time, what has gone wrong here and why

A

There as been inadequate fixing here and some non sensitise crystals are left behind because of this

93
Q

Give 4 Advatages of digital radiograph

A

No need for chemical processing
Easy storage and archive of images
Easy back up of images
Easy transfer/ sharing of images

94
Q

Give 4 disadvantages of digital radiography

A

Risk of data/corruption loss
Image enchantment can create misleading images
Requires diagnostic level computer monitors for optimal viewing
Hard copy print outs generally have lower image quality

95
Q

What are three purposes of extra-oral radiography

A
  • imaging larger sections of the dentition
  • alternative when patient is unable to tolerate intra-oral radiography
  • imaging non dentoalveolar regions
96
Q

There are two terms for angulation of the beam, true and oblique what is the difference

A

True = perpendicular to the head

Oblique = not perperpendicualr to the head

97
Q

How may degrees difference is there between the Frankfort plane and the orbitomeatal line

A

10 degrees

98
Q

What is the cephalogram unit designed to do

A

Produce a standardised and reproducible radiograph

99
Q

What is the purpose of the cephalostat

A

It ensures standardised positioning off equipment and patients head

Avoids discernpanies taken by different members of staff and reduces magnification/distortion of the image

100
Q

What is the standardised distance from the receptor to the X-ray foal spot to minimise magnification

A

1.5-1.8 metres

101
Q

If we wanted to view the facial soft tissues on a cephalogram more clearly how do we solve the problem that exposure settings are optimised for the hard tissues

A

Place an aluminium wedge filter in the unit to attentuate the specific area of the beam exposing the facial soft tissues

102
Q

What are we aiming to do with collimating

A

Reduce the dose as much as possible

The field of view should not be bigger than what is clinically required

103
Q

What is oblique lateral radiography and why not commonly used

A

This provides view of posteior jaws without the superimposition of hte contralateral side

This is uncommon nowadays as it is difficult to. Master the technique and it is superseded by panoramic radiographs

104
Q

How can gutta percha be used to. Aid in radiogrpahic localisation

A

It can be placed into a sinus opening to see where it is drawing

105
Q

What is the definition of parallax

A

An apparent change in the position of an object, caused by a real change in the position of the observer

106
Q

What is the mnemonic to aid in working out parallax

A

SLOB - Same lingual opposite buccal

PAL - my pal goes with me

107
Q

What are the equivalent views for horizontal tube shift in the parallax technique

A

2 periapicals
2 bitewings
2 oblique occlusals ( with different central points)

108
Q

What are the two different views for vertical tube shift in the parallax technique

A

Panoramic and oblique occlusal

Panoramic and lower periapical

109
Q

If the radiographic image has white areas around the edges what do you suspect has happened there?

A

Delamination

Separation of the phosphor layer from the base plate
Mishandling or getting wet and dry ing up

110
Q

Y does damage on film imaging often appear has black marks?

A

Due to the sensitisation of the radiogrpahic emulsion

111
Q

What is a step wedge

A

It is a type of object used to check image quality/contrast, it has overlapping layers of lead foil

112
Q

What are the 3 parts of quality assurance

A

1.image quality rating
2. Image quality analysis
3. Reject analysis

113
Q

What is cone cutting and what are some reasons it may happen

A

This is a collimation error

  • there is incorrect assembly of receptor holder
  • incorrect alignment between X-ray tube and receptor holder
  • incorrect orientation of rectangular colliation
114
Q

In lateral cephalograms the X-ray beam is perpendicular to the receptor and what facial plane

A

The mid saggital plane

115
Q

What group of people does IRR17 deal with

A

Deals with occupational exposures of the GENERAL PUBLIC

116
Q

IRMER17 deals with what

A

Medical exposures of patients

117
Q

Who is IRR17 enforced by

A

Health and safety executive

118
Q

Who is IRMER17 informed by

A

Health improvement Scotland

119
Q

In relation to radiation exposure what is a ‘ carer and comfortor’’

A

Individuals who ‘ knowing and willingly’ exposure to ionising radiation through support and comfort of those undergoing the exposure

120
Q

IRMER17 requires that all exposures are ALARP, whose responsibility is this?

A

The practioner and the operator

Clinical Dental Science BDS3 (7 decks)

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