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Year 3 Radiography > Dental x ray set, conventional image receptors and processing > Flashcards

Dental x ray set, conventional image receptors and processing Flashcards

(49 cards)

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1
Q

what is used for filtration of x ray beam? (be specific)

A
  1. 5mm aluminium below 70kV

2. 5mm aluminium above 70kV

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2
Q

purpose of filtration 2

A
  • removes low energy photons

- decreases dose to pt

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3
Q

function of rectangular collimator

A

matches beam size to image receptor

–> reduces dose by 50%, stops beam being wasted

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4
Q

5 things on x ray control panel

A
  • on/off switch
  • timer
  • exposure time selection
  • warning lights/audible signals
  • exposure button
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5
Q

what determines

a. quality
b. quantity of x ray photons

A

a. quality: kV

b. quantity: mA (tube current)/time

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6
Q

effect of higher kV (higher power given to electrons) 3

A
  • decrease pt dose
  • decrease contrast (more electrons pass through dense tissue so less contrast with soft tissue)
  • increase scatter
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7
Q

effect of higher mA or time 2

A
  • increase pt dose

- increase film blackening

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8
Q

should x rays use AC or DC ? why?

A

DC

must have positive voltage so electrons all flow in same direction and have high energy

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9
Q

4 advantages of constant potential

A
  • xray production per unit time more efficient
  • more high energy photons per exposure
  • fewer low energy harmful photons produced
  • shorter exposure times
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10
Q

what shape of beam is used and why

A

neat parallel beam (not divergent)

–> minimal magnification, smaller area irradiated

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11
Q

2 types of conventional image receptors

A
  • direct action film: x ray photons interact with film

- indirect action film: x ray photons interact with intensifying screen producing light which then interacts with film

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12
Q

what size x ray film to use for

a. anterior teeth
b. posterior teeth
c. occlusal radiography

A

what size x ray film to use for

a. anterior teeth: 0,1
b. posterior teeth: 2
c. occlusal radiography: 4

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13
Q

2 functions of lead foil

label film packet (see lecture)

A

reduce scatter

reduce dose

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14
Q

what does dot on x ray tube show and why

A

location of x ray tube

must have 20cm between target and tube

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15
Q

explain scatter

A

x rays pass through desired dense tissue, bounces back off other structures –> poor quality image

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16
Q

cross section of x ray film

A 
protective coating
emulsion
adhesive
transparent plastic base
adhesive
emulsion
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17
Q

2 mixtures used for the emulsion

A
  • silver halide crystals in gelatin matrix (90%)

- silver iono-bromide (10%)

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18
Q

effect of silver iono bromide

A

increases sensitivity

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19
Q

how does the emulsion work

A

x ray/light photons sensitize silver halide crystals that they strike forming a latent image
sensitized crystals reduced to black metallic silver in the developer

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20
Q

order of letters of film speed and colour

Study These Flashcards
A

D speed (blue) –> E speed (1/2 dose of D speed) –> F speed (60% dose of pink speed) –> digital (50% dose of F speed)

21
Q

which of these is currently used for intraoral x rays?

22
Q

what effect does film speed have on image quality and why

Study These Flashcards
A

faster film–> lower quality image
because film speed ∝ size (and number) of silver halide crystals in soln
so larger crystals –> faster film but less fine image

23
Q

how do indirect action films work

Study These Flashcards
A

x ray photons interact with an intensifying screen –> light produced –> interacts with film (film is sensitive to light)

24
Q

describe what an indirect action cassette looks like/made of and what each part does

Study These Flashcards
A

light-tight aluminium or carbon fibre casings. contains sandwich:
1st intensifying screen, picks up lower energy photons
cassette film
2nd intensifying screen, picks up higher energy photons

25
when are indirect action films used and why
when there's a thicker part of body to penetrate (eg jaw, EXTRAORAL X RAYS) so would have to increase exposure too much if direct action film was used
26
what are intensifying screens made of and why
fluorescent phosphors (emit light when excited by x rays) embedded in a plastic matrix
27
effect of intensifying screens on pt dose and why
decreases pt dose: one x ray photon --> many light photons (so less x ray photons required to produce an image than with direct action film)
28
disadvantage of indirect action film/ intensifying screens
decreased image resolution
29
define image resolution
ability to differentiate between different structures that are close together on a radiograph
30
resolution of a. direct action film b. indirect action film
a. direct action film: 10 line pairs per mm | b. indirect action film: 5 line pairs per mm
31
how to calculate intensification factor
exposure required when screens not used/ | exposure required with screens
32
compare rare earth screens and calcium tungstate screens
rare earth screens: 5x faster than calcium tungstate screens --> lower dose to pt
33
why must film be matched to screen with rare earth screens?
different phosphors emit different coloured lights, so film must be able to detect type/colour of light emitted
34
what does film processing do?
turn invisible latent image --> visible radiographic image
35
advantages of automatic processing over manual processing 4
- time saving (20 mins --> 5 mins) - no darkroom rqd - controlled standardised processing conditions - replenishment of chemicals is automatic
36
5 stages of film processing
1. development (2. clearing) 3. fixation 4. washing 5. drying
37
explain the development stage
sensitised silver halide crystals in the emulsion are converted to black metallic silver to produce the black/grey parts of the image
38
what can cause overdevelopment? 3
- conc of soln too strong - too long - too hot
39
what can cause underdevelopment? 4
-conc of soln too weak, because it is oxidized by air over time --> less effective (too old) -too cold -not long enough
40
how often should developing soln be changed and why
every 14 days | alkaline soln pH 10.5 is oxidized by air, weakening soln --> underdevelopment
41
describe appearance of a. overdeveloped b. underdeveloped film
a. overdeveloped: black, can't see image | b. underdeveloped film: white, image unclear
42
explain the clearing stage of processing
-unsensitised silver halide emulsion is removed to reveal the transparent/white parts of image and emulsion is hardened
43
fixation stage of processing and conditions required
-fixer anchors silver grains to film base | acidic pH 4-4.5
44
compare clearing and fixing time and fixing time for manual processing
fixing time is double clearing time (usually 8-10 mins for manual processing)
45
describe under-fixed film
greenish yellow/ milky | may discolour to brown over time
46
why must film be washed
remove any residual fixer (otherwise film becomes stained brown)
47
what causes chemical splashes 2
(usually in manual processing) - fixer splashes prior to development - developer splashes
48
what causes films to stick together in automatic processing
not leaving long enough before putting films in processor
49
what causes light fogging?
opening film packet in light

Year 3 Radiography (9 decks)

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