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3rd Year > Radiography > Flashcards

Radiography Flashcards

1
Q

Describe the 3 radiation protection principles.

A

Justification- must do more good than harm.

Optimised- ALARP- As low as reasonably practiciple

Limitation- individual dose limits are used to ensure no one has an unacceptable exposure.

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2
Q

What is the inverse square law and why is it relevant to radiographs?

A

The X-ray follows this law.

That the further away from the source, the intensity of the x-ray reduces.

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3
Q

What is the pattern of attenuation?

A

This is how we produce a radiographic image using the pattern produced by the interaction of x-rays with matter.

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4
Q

Compare the ways that an x-ray can be absorbed?

A

Full absorption (e.g. amalagam showing up white on an x-ray)

Partial absorption and scatter- individual components of the beam change direction.

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5
Q

Name this type of radiograph

A

Bitewing

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6
Q

Name this type of radiograph

A

Periapical

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7
Q

Name this type of radiograph?

A

Occlusal. There are 2 types:

  • True - cross sectional
  • Oblique- image receptor is put in the occlusal plane.
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8
Q

Name this type of radiograph

A

Panoramic

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9
Q

Name this type of radiograph

A

Cephalometric

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10
Q

Name and describe the two legislations in the uk for radiation.

A

IRR17- for the general public and occupational exposure (those paid to be exposed to radiation)

  • Employer must (register for x-rays, consult a radiation protection advsier and ensure radiation risk assessments are carried out)
  • Controlled areas must be defined & local rules for that area.

IRMER- For Medical exposure of patients and those not paid for exposure (e.g. patient’s parents)

  • Patient identifcation procedures
  • Staff entitlement procedures
  • procedures to provide information.
  • 4 roles (referrer/ practioner/ operator/ employer.)
  • Clinical evaluation.
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11
Q

How often and why do we test radiographic equipment?

A

To ensure It :

  • is working correctly
  • Is administering the expected dose level.

We test it:

  • Every 3 months by a staff member
  • Every 1-3 years by specialist staff.
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12
Q

What is the ideal projection geometry and why can we not achieve it?

A

These are the principles we want for achieving a good image:

  • That the image receptor and object are in contact- cannot fully contact as the tooth is supported by bone.
  • That the x-rays are a parallel beam- x-ray beam is divergent so cannot be parallel.
  • That the image size is indentical to the object size- we can’t do this because the divergent beam causes mangification.
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13
Q

what is paralleling.

A

Where the image receptor and object are parallel but not touching.

The central ray is perpendicular to the long axis of the tooth.

Outer rays are at slight angles (the x-ray is divergent)

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14
Q

What is the FSD?

A

The focus to skin distance. This helps us line up the x-ray beam with the patient.

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15
Q

What FSD do we use for Radiography and why?

A

We use a long FSD to reduce magnification.

The longer FSD makes the x-ray beam near parallel compared to the diverging x-ray beam of a short FSD.

e.g. 20cm

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16
Q

What is rectangular collimation?

A

A device that reduces the dose of the x-ray and allows us to control the shape and size of the x-ray beam.

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17
Q

What is the blue film holder used for?

A

Anterior teeth.

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18
Q

What is the yellow film holder used for?

A

Posterior teeth

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19
Q

What is the red film holder used for?

A

Bitewings.

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20
Q

What are the 3 components of a film holder?

A

Bite block

Beam aiming device

Image receptor support

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21
Q

Compare the curve of Spee and the curve of Monsoon?

A

Curve of spee is the upward slope of the teeth as seen in a radiograph

Curve of monsoon is that the buccal cusps of molars are slightly higher than the palatal cusps.

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22
Q

What is the bisecting angle technique?

A

When the receptor and the object are touching but not parallel.

They are touching at the crown & far apart at the apex.

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23
Q

What are the soft tissue checkpoints for a maxillary occlusal radiograph?

A

Alatragus line should be paralell to the floor

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24
Q

what are the soft tissue checkpoints for a mandibular occlusal?

A

Corner of the mouth to the tragus of the ear are parallel.

Head is tilted backwards.

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25
Q

What is the horizontal angle we want for radiographs?

A

90* to the line of the arch.

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26
Q

What is the centuring point of the maxilla for a periapical

A

On the ala tragus line

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27
Q

What is the centuring point of the maxilla for an oblique occlusal?

A

1cm above the ala-tragus line.

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28
Q

What is the centuring point of the mandible for a periapical

A

1cm above the lower border of the mandible

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29
Q

What is the centuring point of the mandible for an oblique occlusal?

A

Through the lower border of the mandible.

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30
Q

Why does the vertical angle drop as you reach the back of the mouth?

A

As the teeth become more upright as we reach the molars.

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31
Q

What is a Dental Panoramic Tomograph?

A

A radiograph which displays details from a specific image layer of the teeth with specific resolution.

Also known as DPT/DPR/OPT

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32
Q

Describe linear Tomography

A

We form images by the continuous movement of the x-ray machine and receptor.

The X-ray machine moves from L to R.

The receptor moves from R to L.

The focal trough is what we want to see and this remains in one place.

We use 2 location centres to achieve this (an anterior and a posteiror location centre)

33
Q

Compare taking panoramic radiographs of anterior teeth and posterior teeth

A

Anterior teeth:

  • Slower beam passage through the teeth
  • Slower image receptor movement to match.

Posterior teeth

  • faster beam passage through the teeth
  • faster image receptor movement to match.

If the speeds don’ t match there will be image distortion.

34
Q

How does the distance from the rotation centre to the teeth affect radiographs?

A
  • It affects the width of the layer in focus (focal trough)
  • Can cause horizontal distortion if the patient is in the incorrect position.
  • Ghost images can be formed.
35
Q

Why is the canine position so important in an OPT?

A

This allows you to prevent distortion of the image by compensating the speed dependent onthe canine position.

36
Q

What are ghost images?

A

A second image of something in the wrong place formed by the beam x-ray going through the back of the object again at the position of the premolars.

It will always be:

  • Higher due to the negative 8* beam angle
  • horizontally magnified (i.e. wider)
  • Further forward.
37
Q

How frequently should you take bitewings for a high risk caries patient?

A

Every 6 months

38
Q

How frequently should you take bitewings for a moderate risk caries patient?

A

Anually

39
Q

How frequently should you take bitewings for a low risk caries patient?

A

Primary teeth (12-18 months)

Permanent teeth (2 years)

40
Q

What does this image show?

A

Cervical burnout.

The Mesial and distal area between the enamel margins and crest of bone appear radiolucent.

This is commonly found in periodontal disease where the drop in bone level creates the larger distance between the enamel margins and crest of bone. There is a lower absorption of x-rays.

This looks similar to root surface caries (but cannot be seen clinically)

41
Q

Distinguish between the two types of restorative mateiral in this radiograph:

A

Brighter is amalgam.

Matter is composite.

42
Q

Compare these two radiographs:

A

Left image- Internal root resorption (results from chronic pulpitis)

Image shows radiolucency within canal space

Right image- External root resorption (originates in the PDL)

image shows radiolucency overlying the root canal.

43
Q

Compare the continuous and characteristic spectrum

A

Continuous spectrum -

Electron gets close to the nucleus & is slowed down and defelected.

Kinetic energy is lost and released as photons (low energy)

Characteristic spectrum

Electron collides with an inner shell electron

Inner shell e- is displaced to an outer shell or completely knocked from the atom.

The atom is unstable so the electrons re-arrange producing the x-ray photon.

44
Q

What is the filament?

A

A cathode (negative) used to pull the electrons towards the positive side of the electron tube.

45
Q

What is the function of the transformer?

A

To increase the voltage from the mains supply to kVp

46
Q

What is the target surround and why do we need it?

A

A copper layer that surrounds the target to remove heat. (99% of the energy produced by the target is heat)

47
Q

What is the function of the evacuated glass envelope?

A

It is a vaccum that prevents the risk of interaction of electrons with air atoms prior to meeting the target.

48
Q

What is the sheilding in a tubehead?

A

This is a led surrounding that absorbs the x-rays in order to cap the dose rate.

49
Q

What is the filtration of the tubehead?

A

An aluminium layer used to interact and get rid of the low x-rays that we don’t want. (the high energy x-rays can travel through this)

50
Q

Compare the process of the Photoelectric and Compton Effects

A

Photoelectric

X-ray photon interacts with an inner shell & disapears

The electron knocked out (photoelectron) has some kinetic energy and can have other interactions.

This leaves an empty space & causes the atom to re-organise.

Characteristic radiation is released due to the movement between shells.

Compton

X-ray photon interacts with an outer shell electron (outer electron is ejected)

There is lots of energy left in the x-ray photon (Scatter photon)

The scatter photons journey is altered as it leaves the atom & it can be involved in other compton or photoelectric reactions. .

51
Q

What is does the photoelectric effect contribute to?

A

The image, as the photons interact with material, resulting in a varied interaction with the image receptor.

52
Q

How does the energy level affect the direction of scattered photons?

A

High energy scatter photons travel forward.

Low energy scatter photons travel backwards.

53
Q

What sort of materials is the compton effect more likely to happen to and why?

A

Dense materials (more electron dense) as it is more likely that an incoming photon is going to bump into the electrons.

54
Q

Compare how the photoelectric effect and Compton effect impact the image and dose.

A

The photoelectric absorption produces the image and increases the dose.

The compton effect only increases the dose.

55
Q

Compare direct and indirect damage to DNA

A

Indirect damage- Radiation interacts with water in the cell to produce free radicals (that cause damage)

Direct damage-Radiation interacts directly with atoms of a DNA molecule.

56
Q

Compare the deterministic effects and Stochastic effects of radiation

A

Deterministic Effect-

Only occurs above a certain dose & the severity is related to the dose.

e.g. hair loss due to chemotherapy

Stochastic Effect-

There is no threshold for the effect.

These can be somatic (causing a disease or disorder)

Genetic (causing abnormalities in descendants)

57
Q

What are tissue weighting factors?

A

A number used to account for the varying sensitivites of different organs and tissues to radiation.

58
Q

Compare the different types of dose

A

Absorbed dose- energy deposited by radiation

Equivalent dose- Dose taking into account the damage to the specific tissue (absorbed dose x tissue weighting factor)

Effective dose- the dose for the whole body (sum of equivalent dose x tissue weighting factor for each organ involved)

59
Q

What is a cephalometric radiograph?

A

A standardised and reproducable form of skull and facial bone radiography

60
Q

What do we use a cephalometric radiograph for?

A

Orthonathic surgery (pre-op and post op)

Patients with skeletal/vertical or antero-posterior discrepancy

Patient’s requiring fixed or functional appliance therapy (for labio-lingual movement of incisors)

Implant planning

61
Q

What is the MSP?

A

Mid sagital plane (Or line)

62
Q

Compare the OM and FP lines.

A

Orbito-meatal line- a line from the outer corner of the eye to the centre of the external auditory meatus.

Frankfort plane- From the external auditory meatus to the lowest part of the infra-orbital rim.

There is a 10° difference.

63
Q

Compare the two types of lateral radiography

A

True-

The film and midsagital line are paralell.

X-ray beam is perpendicular to them both.

Oblique-

The film and MSP are not parallel

X-ray beam is oblique to both of them.

uncommon.

64
Q

What is the distance between the source and the patient’s MSP for a cephalometric radiograph

A

5 feet or 152.4cm

65
Q

What does this image show?

A

An unerrupted third molar.

66
Q

What does this radiograph show?

A

A permanent canine coming through (They are found higher up than premolars)

67
Q

What does this radiograph show

A

The tooth has erupted but the root is not fully formed.

68
Q

Which teeth are more likely to be congenitally absent?

A

the last tooth of each group of teeth

Lateral incisor

Second premolar

third molar

69
Q

How do we grade a radiograph?

A

You need to know what the radiograph should contain. Then grade.

A- Diagnostically acceptable (No errors/ minimal errors/sufficient quality to answer the Q)

N- Diagnostically unacceptable .

70
Q

What is radiographic localisation?

A

Using radiographs to determine the position.

71
Q

When would we use radiographic localisation?

A

To find out:

  • Position of unerupted teeth
  • Location of roots/root canals
  • Relationship of pathological lesions
  • Trauma
  • Soft tissue swellings.
72
Q

Compare the two view choices used for radiographic localisation?

A

Right angle- using two radiographs at right angles to each other. (e.g. panoramic and lower true occlusal

A known projection geometry -This requires a horizontal or vertical tube shift in order to interpret the image (but we need to know the difference in projection)

73
Q

What is paralax?

A

where an aparent change in the position of the object is caused by an actual change in the observers position.

74
Q

What are the rules of thumb for paralax

A

My PAL goes with me.

If the object in question moves in the same direction as the source (it is LINGUAL/PALATAL)

75
Q

Compare the two types of tube shift.

A

Horizontal tube shift- The same radiographic view but centred on different places. (e.g. two periapicals)

Vertical tube shift- different views (e.g. a panoramic and an oblique occlusal)

76
Q

Compare paralleling and bisecting angle technique

A

Parallelling- the image receptor and object are not touching but are parallel.

Used for periapicals/bitewings

disadv-more limited by mouth anatomy & if the source is too close we get magnification.

Bisecting techinque- the receptor and object are touching but not parallel.

Used for: Periapicals/oblique occlusals/true occlusals.

Disadv- wrong angle can cause distortion.

77
Q

What are contingency plans and why do we need them?

A

These are immediate actions to be taken in the instance of a reasonably foreseeable radiation incident.

So we know what do to if certain incidents occur.

78
Q

What is meant by dose monitoring?

A

This is montoring :

  • The staff who enter the controlled area (should have an annual personal dose of 1msv)
  • The controlled area itself (is it big enough? Do we need to count adjacent rooms aswell)
79
Q
A

3rd Year (63 decks)

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