Dental x ray set, conventional image receptors and processing Flashcards Preview

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

Flashcards in Dental x ray set, conventional image receptors and processing Deck (49):
1

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

1.5mm aluminium below 70kV
2.5mm aluminium above 70kV

2

purpose of filtration 2

-removes low energy photons
-decreases dose to pt

3

function of rectangular collimator

matches beam size to image receptor
--> reduces dose by 50%, stops beam being wasted

4

5 things on x ray control panel

-on/off switch
-timer
-exposure time selection
-warning lights/audible signals
-exposure button

5

what determines
a. quality
b. quantity of x ray photons

a. quality: kV
b. quantity: mA (tube current)/time

6

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

-decrease pt dose
-decrease contrast (more electrons pass through dense tissue so less contrast with soft tissue)
-increase scatter

7

effect of higher mA or time 2

-increase pt dose
-increase film blackening

8

should x rays use AC or DC ? why?

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

9

4 advantages of constant potential

-xray production per unit time more efficient
-more high energy photons per exposure
-fewer low energy harmful photons produced
-shorter exposure times

10

what shape of beam is used and why

neat parallel beam (not divergent)
--> minimal magnification, smaller area irradiated

11

2 types of conventional image receptors

-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

12

what size x ray film to use for
a. anterior teeth
b. posterior teeth
c. occlusal radiography

what size x ray film to use for
a. anterior teeth: 0,1
b. posterior teeth: 2
c. occlusal radiography: 4

13

2 functions of lead foil

label film packet (see lecture)

reduce scatter
reduce dose

14

what does dot on x ray tube show and why

location of x ray tube
must have 20cm between target and tube

15

explain scatter

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

16

cross section of x ray film

protective coating
emulsion
adhesive
transparent plastic base
adhesive
emulsion

17

2 mixtures used for the emulsion

-silver halide crystals in gelatin matrix (90%)
-silver iono-bromide (10%)

18

effect of silver iono bromide

increases sensitivity

19

how does the emulsion work

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

20

order of letters of film speed and colour

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

which of these is currently used for intraoral x rays?

F speed

22

what effect does film speed have on image quality and why

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

how do indirect action films work

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

24

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

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