Dental X-ray set

Question 1

Parts of X-ray set

Answer 1

Tube head
Positioning arms
Control panel

Question 2

Filtration requirements

Answer 2

Less 70kV is 1.5mmAl
More 70kV is 2.5mmAl
Removes low energy photons
Decreases dose to patient

Question 3

Why is rectangular collimator used?

Answer 3

Match beam size to image receptor to decrease dose to patient
Decreases dose by 50%

Question 4

kV

Answer 4

Quality/ penetrating power of beam

Inc kV = decrease dose, dec contrast, inc scatter. More shades of grey

Question 5

mA/time

Answer 5

Quantity of photons.

Inc mA/time = inc patient dose, inc film blackening.

Question 6

ADV of constant potential

Answer 6

Dec exposure time and low E Photons
More high E Photons
Xray production more efficient

Question 7

Spacer cone or beam indicating device (BID)

Answer 7

OLD
Pointed cone with short focal skin distance (fsd)
Divergent beam - image magnification and greater area irradiated
NEW
20cm come long fsd
Near parallel beam - minimal magnification and less area irradiated

Question 8

Direct action film

Answer 8

Xray photons interact with film

Question 9

Indirect action film

Answer 9

Xray photons hit intensifying screen. This produces light which interacts with film.

Question 10

Emulsion

Answer 10

90% silver halide crystallise gelatine matrix
10% silver todo-bromide crystals (inc sensitivity)
Xray/light sensitise silver halide crystals giving latent image
in developer: silver halide go to black metallic silver

Question 11

Films speed

Answer 11

Most used: F speed, rectangular collimation
Faster = less dose to patient
Speed is a function of no. and size of crystals in emulsion
larger crystals = faster film BUT some loss of quality

Question 12

Cassettes

Answer 12

Light tight aluminium or carbon fibre casing
As intensifying screens both side of film this reduces patient exposure - one X-ray gives lots of light P therefore less X-ray P needed

Question 13

Image resolution def

Answer 13

Ability to differentiate between different structures that are close together on the radiograph

Question 14

Direct and indirect resolution

Answer 14

Direct - 10 line pairs per mm

Indirect - 5 line pairs per mm

Question 15

Intensification factor

Answer 15

Exposure required when screens not used/

exposure required with screens

Question 16

Rare earth screens

Answer 16

x5 faster than calcium tungstate
Terbium - emit Green light
Thulium - emit Blue light
Yttrium - Ultraviolet

Question 17

Film processing

Answer 17

Invisible latent image to visible radiographic image

Question 18

Stage 1:

Answer 18

DEVELOPMENT
Sensitised silver halide crystals in emulsion go to black metallic silver (black/grey parts of image)
Important sol conc, time, temp
Too strong/long/hot = overdeveloped, dark film
Too weak/ cold/ old = underdeveloped, pale film

Question 19

Developing solution

Answer 19

Alkaline pH 10.5
Oxidised over time - less effective
change every 14 days

Question 20

Stage 2:

Answer 20

FIXATION
Unsensitised silver halide emulsion removed to reveal transparent/white parts of image. Emulsion hardened.
Fixer anchors silver grains to base
Acidic pH 4-4.5

Question 21

Fixing and clearing 3?

Answer 21

Fixing not as critical as developing
CLEARING: Time to remove unsensitised silver bromide crystals from film
Fixing is x2 clearing time (8-10mins)
Underfixed: greenish yellow/milky

Question 22

Stage 4:

Answer 22

WASHING
Washed to remove any residual fixer
Remaining fixer - brown

Question 23

Processing faults

Answer 23

Light fogging
film stuck together
marks from dirty rollers
splashes: developer - grey fixer - white

Question 24

Colours through process

Answer 24

Non - exposed: Green silver halide emulsion
Exposed: Green sensitised/ non-sensitised silver halide emulsion
Developed: Black metallic silver/ green silver halide
Fixer: White/clear and black metallic silver
Wash and dry: Black and white image