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BDS3 CLINICAL Radiology > Intra-oral techniques and Paralleling > Flashcards

Intra-oral techniques and Paralleling Flashcards

1
Q

If the ideal projection geometry is met what will this result in

A

the image size will be identical to the object size

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2
Q

What is the ideal projection geometry

A

Image receptor and object in contact and parallel

Parallel beams of X-rays coming towards the patient and the image receptor

X ray beam is perpendicular to object plane and image receptor plan

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3
Q

What are problems in projection geometry

A

image receptor and object not in contact
the beams of X-rays are NOT parallel
X -ray beam central ray may nor may not be perpendicular to the object plane and image receptor
Image size is not identical to object size

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4
Q

Why can the image receptor and object not fully be in contact

A

because the tooth is supported by bone so you cannot contact all of it

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5
Q

Why are beams of X-rays not parallel

A

X-ray beams are divergent beams so the rays will not be parallel

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6
Q

Why is the image size not identical to object size

A

due to magnification caused by the divergent beam

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7
Q

What type of X-ray does not have magnification

A

cone beam ct

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8
Q

What are two solutions to the problems in projection geometry

A

paralleling technique

bisecting angle technique

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9
Q

What is the paralleling technique

A

the image receptor and object are parallel but they are not touching

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10
Q

What is the bisecting angle technique

A

image receptor and object partially in contact but not parallel to each other

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11
Q

Are all beams parallel in the paralleling technique

A

no only the central ray is perpendicular to the long axis of the tooth, the outer rays are not quite perpendicular

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12
Q

Why does magnification happen

A

Due to the image receptor and the object being some distance apart, there is potential for undesirable magnification

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13
Q

What is the fsd

A

distance between the focal spot of the x-ray tube (where x-rays are produced) marked with a red dot on the intra-oral x-ray head to the skin surface of the patient

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14
Q

Wha can be done to reduce magnification

A

Use long X-ray focus skin distance

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15
Q

What is the minimum length for X-ray focus-skin distance

A

20cm

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16
Q

What does the long X-ray focus skin distance allow for

A

more parallel, non-diverging X ray beam as the outer part of the beam are not quite as divergent leading to less magnification

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17
Q

Where should the beam aiming device of the film holder be placed

A

close to but not actually touching the patient

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18
Q

How do you measure the fsd

A

you measure the mark on the outside of the tube head to the patient end of spacer cone

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19
Q

What should rectangular collimation be combined with

A

beam-aiming devices and film holders

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20
Q

What is the benefit of film holders, BAD and RC

A

Dose reduction
Improved quality
Fewer rejects

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21
Q

What are the different colors of film holders

A

red blue and yellow

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22
Q

What part of the film holder is color coded

A

bite block, beam aiming device and rod

23
Q

What is the blue FH

A

anterior periapicals

24
Q

What is the red FH

A

bitewings

25
Q

What is the yellow FH

A

posterior periapicals

26
Q

What is the image receptor support for

A

holding and supporting the image receptor

27
Q

What is the bite block for

A

what the patients bite on

28
Q

How are the film holders cleaned

A

autoclaved

29
Q

How can you tell if you have assembled the film holder correctly

A

○ If you look through the circle you should see the support for the image receptor right in the middle, if you don’t then something is wrong

30
Q

What does incorrect film holder assembly result in

A

coning off

31
Q

What do endodontic film holders consist of

A 
○ Image receptor support (receptor vertical or horizontal) 
○ Bite block
○ Beam-aiming device
○ Connecting rod - no colour 
Autoclavable
32
Q

What does endodontic film holders also have

A

○ Basket to support instrument heads or gutta percha points so that the patient does not bite the tooth with the files in it, the basket ensures the teeth are kept apart and protect the heads of the instruments

33
Q

What is collimation

A

controlling the shape and size of x ray beam

34
Q

Why does the beam aiming device have rectangular marks

A

so that it can be lined up easily with the x ray device

35
Q

What machines should RC be on

A

should be provided on new equipment and retrofitted to existing equipment

36
Q

What is the collimator made of

A

lead

37
Q

What are the shapes of collimator

A

circular or rectangular

38
Q

What is the maximum diameter of a circular collimator

A

60mm

39
Q

What is the silver bit of the collimator that lets x ray out

A

aluminium

40
Q

Why does rectangular collimator emit less radiation

A

Reduction in surface area

but is more technically difficult as need to ensure everything is lined out

41
Q

What are the different sizes of image receptors for periapicals

A

Size 0 vertical anteriors image receptor (blue holder) - smallest, use that with long axis vertical for anterior teeth

Size 2 horizontal posteriors image receptor (yellow holders) - bigger, use that for long axis going horizontally

42
Q

What is the procedure for a periapical

A

Select the film holder and correct image receptor
Assemble correctly - be careful with sensors
Position patient at right height, open wide
Position against teeth of interest, parallel to line fo arch and long axis of tooth

43
Q

Where should beam aiming device be when putting film holder into mouth

A

at free end

44
Q

How do you position film holder into mouth

A

○ Bite block against the teeth
○ Cotton roll between bite block and teeth on opposite side to stabilise
○ Beam aiming device to patient (was previously on the free end); close to but not touching
○ Rectangular collimator: correct orientation to match image receptor, and spacer cone close to beam-aiming device
○ Align tube head - check from 2 directions, for a periapical check from underneath and from infront

45
Q

Summarise the paralleling technique

A
  • Image receptor and object parallel but not in contact for a paralleling periapical
    • Image receptor and object some distance apart - potential for undesirable magnification
    • Use long X-ray focus-skin (fsd) distance to reduce magnification - at least 20cm
    • Requires use of film holders, cannot do it without them
      Stabilise with cotton roll between bite block and teeth in arch opposite to that being x-rayed, if you put it on the wrong side then there is risk of not getting the apex of the tooth in the image
46
Q

What is the ideal bitewing

A
  • Of the side teeth (premolars and molars)
    • Symmetry of upper and lower teeth (film holder should guarantee this)
    • Minimal overlap of adjacent teeth
    • Want to see inter-dental bone
      One or two per side
47
Q

Describe procedure for taking bitewing

A

Select film holder (red holder) and image receptor (long axis horizontal for both)

Assemble correctly

Position against lower teeth, parallel to line of arch, tongue out the way

Front edge of film packet mesial to canine/premolar contact

48
Q

What are the different sizes of image receptor

A

size 2 (adults) and size 0 (children)

49
Q

Describe how the film holder is positioned in the mouth for bitewings

A

○ Patient to bite together
○ Beam-aiming device to patient, again make sure it is close but not touching
○ Rectangular collimator orientation correct
○ Spacer cone to beam-aiming device
Align tube head - check from 2 directions. In front and from below

50
Q

What are the critical points for bitewings

A
  • Image receptor is parallel to the line of arch
  • Central ray at 90 degrees to arch
    Vertical angle controlled by the film angle
    If no film holder then vertical angle needs to be +5-10
51
Q

Why do you need to change vertical angle for bitewing if no film holder

A

takes into account curve of Monson

52
Q

What is curve of spee

A

anterior-posterior

○ Curves up posteriorly
○ Produces a happy smile
○ Useful to us when we are trying to see what way the radiograph is

53
Q

What is curve of monson

A

buccal-lingual

Influences X-ray technique e.g bitewings and panoramic radiography (Panoramic vertical angle is negative to occlusal plane (-8)
Curve of Monson influences the position of the film holder which determines the vertical angle

54
Q

How can you determine orientation of x-ray

A

curve of spee
look at the molars, you can’t see how many roots there are in the upper one, only in the lower and this is due to the mesial distal roots of the lower so this is the most reliable way of checking the orientation of the X-rays

BDS3 CLINICAL Radiology (16 decks)

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