Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS3 Radiology > paralleling > Flashcards

paralleling Flashcards

1
Q

what is the ideal projection geometry

A

image receptor and object in contact and parallel

parallel beam of X-rays

X-ray beam perpendicular to object plane and image receptor
- image size identical to object size

cannot happen
- tooth in isolation, image receptor directly behind, 3 X-ray beams come in parallel to each other and perpendicular to long axis of tooth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

projection geometry problems

A

image receptor and object NOT in contact

beam of X-rays NOT PARALLEL

X-ray beam central ray MAY or MAY NOT be perpendicular to object plane and image receptor

image size NOT identical to object size DUE to MAGNIFICATION - DIVERGENT BEAM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

2 solutions to problems in projection geometry

A

paralleling technique
- image receptor and object parallel

bisecting angle technique
- image receptor and object partially in contact and not parallel to each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

paralleling technique

A

image receptor and object parallel but not in contact

X-ray beam central ray perpendicular to long axis of tooth and image receptor, but outer rays not quite perpendicular due to divergent beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

divergent X ray beams due to

A

image receptor and object some distance apart
- potential for undesirable magnification

Short focus to skin distance (fsd) – measured on machine

  • spacer cone now long focus skin distance
  • sticks out some way to help focus beams
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

focus-skin distance

A

use long X-ray focus - skin distance (fsd) to reduce magnification

at least 20 cm – part of regulations with 60 or 70kV

N.B. Beam-aiming device of film holder should always be close to, but not actually touching patient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

location of focus

A

use long X-ray focus - skin distance (fsd) to reduce magnification
- at least 20 cm,

  • may be 30cm
    longer distance = more parallel rays

Measure from mark on outside of tube head (here a red dot) to patient end of spacer cone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

3 reasons why rectangular collimation should be combined with beam-aiming devices and film holders

A

dose reduction

improved quality

fewer rejects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

2 types of film holders

A

rinn film holders (current)

endodontic film holders

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

rinn film holders

A

currently used

colour coded

  • blue - anterior
  • yellow - posterior
  • red - bitewing

components (all autoclavable)

  • image receptor support – perpendicular part at end
  • bite block – rigid section by image receptor support
  • beam-aiming device with rectangular guides – circular, slides, marks to show where corners of rectangle of X-ray machine head should line up
  • connecting rod – different for colours
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

components of rinn film holders

A

image receptor support – perpendicular part at end

bite block – rigid section by image receptor support

beam-aiming device with rectangular guides – circular, slides, marks to show where corners of rectangle of X-ray machine head should line up

connecting rod – different for colours

all components are autoclaveable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

blue rinn holder

A

anterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

yellow rinn holder

A

posterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

red rinn holder

A

bitewing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

endodontic film holders

A

green

image receptor support (receptor vertical or horizontal)

bite block

beam-aiming device

connecting rod – no colour

autoclaveable

PLUS basket to support instrument heads or gutta percha points, unable to bite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

film holder assembly

A

critical

correct = good result
- see support of image receptor in middle of circle

incorrect = coning off

17
Q

retangular collimations

A

should be provided on new equipment, and retro fitted to existing equipment.

18
Q

collimator made of

A

lead
- circular or rectangular diaphragm

prevents X-rays escaping (lead absorbs)

max. beam diam. of circle
60mm at patient end of spacer cone

19
Q

beam size for circular

A

no greater than 60mm diameter at patient end of spacer cone

area = 2828 sqmm

20
Q

beam size for retangular

A

2000 sqmm

30% reduction compared to circular
- requires greater care on lining up

21
Q

how to take a periapical

A

select film holder and image receptor

  • size 0 vertical anteriors (blue holder)
  • size 2 horizontal posteriors (yellow holder, larger)

assemble correctly

position against teeth of interest, parallel to line of arch and long axis of tooth
- keep beam aiming ring far away so not to hit pt

bite block against teeth

  • stability to film holder
  • long axis parallel to long axis of teeth

cotton roll on opposite side of biteblock to stabilise

beam-aiming device to patient; 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
side and underneath

22
Q

paralleling technique summary

A

image receptor and object parallel but not in contact

image receptor and object some distance apart
- potential for undesirable magnification

use long X-ray focus - skin (fsd) distance to reduce magnification
- at least 20 cm

requires use of film holders

stabilise with cotton roll between bite block and teeth in arch opposite to that being X-rayed

23
Q

tongue and X-ray

A

move out of way as will interfere with image

24
Q

bitewings show

A

side teeth (premolars and molars)

symmetry of upper and lower teeth

minimal overlap of adjacent teeth

inter-dental bone

one or two per side

25
Q

how to take bitewings

A

select film holder (red holder) and image receptor
- size 2 adults
- size 0 small children
long axis horizontal

assemble correctly

position against lower teeth, parallel to line of arch

front edge of film packet mesial to canine/premolar contact

patient to bite together

beam-aiming device to patient – close not touching

rectangular collimator orientation correct

Spacer cone to beam-aiming device

align tube head - check from 2 directions
- front and downwards

26
Q

critical points for taking bitewings

A

image receptor parallel to line of arch

central ray at 90 degree

vertical angle controlled by film holder

no film holder – is possible
- determine vertical angle + 5-10 degrees relative to occlusal plane - Monson

27
Q

occlusal curve of spee

A

antero-posterior

  • curves up posteriorly
  • produces a happy smile

tell orientation of X rays

also Bone between root – therefore mesial and distal root, thus lower

28
Q

occlusal curve of Monson

A

bucco-lingual

influences X-ray technique e.g.bitewings and panoramic radiography (Panoramic vertical angle is negative to occlusal plane: minus 8 degrees)

BDS3 Radiology (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions