film imaging and processing

Question 1

image receptor (film)

Answer 1

Protective coat 
emulsion
adhesie coating
base
'repeat'

Question 2

protective coat

Answer 2

transparent layer (usually gelatine) to protect emulsion

Question 3

emulsion

Answer 3

sliver halide crystals held in gelatine suspension

-reacts to light

Question 4

geletine

Answer 4

increases sensitivity of crystals

provides even suspension for crystals

Question 5

adhesive layer

Answer 5

sticks emulsion to base

Question 6

base

Answer 6

translucent blue plastic tp make the structure sturdy

Question 7

image receptor screen

Answer 7

protective layer
reflective layer
phosphor layer
protective layer x ray film
...

Question 8

protective layer

Answer 8

transparent layer to protect phosphor

Question 9

reflective layer

Answer 9

reflects light back towards film

• increases sensitivity
• allows reduction of the dose due to scatter

Question 10

image receptor screen interection steps

Answer 10

An x ray photon will likely interact in the phosphor layer above or below the film converting its energy to may light photons

• the photons are emitted in all directions (might hit reflective layer or not)
• those that head towards the film may activate the silver halide in the emulsion
• as the photons spread out from the interaction point they will cause a larger area of blackening
• this reduces the resolution of the system

Question 11

what does speed depend on

Answer 11

thickness of phosphor layer in screen
crystal size in emulsion
conversation efficiency
light absorbing dyes within screen

Question 12

image formation steps

Answer 12

When an x ray photon hits a crystal in the emulsion an electron from an Br ion gets enough energy to escape
- the electron moves to a defect in the crystal or to a Ag2S impurity known as a sensitivity speck
- this becomes – charged and attracts a mobile silver ion from within the crystal and to form an silver atom
- this Ag atom then acts as a trap for a second electron and the process is repeated
- by this small deposits of silver will have formed those crystals hit by an xray photon
- these crystals will then be more sensitive to the developer and the whole crystal will be blackened (not just the silver atoms)
can vary the crystal size – more dose by using smaller more crystals compared to larger crystals

Question 13

developer characterisics

Answer 13

alkali
acts as reducing agent
converts remaining silber ions to silver atoms (adding e-)

Question 14

what does washing do

Answer 14

stops developer working on film

Question 15

fixing

Answer 15

acid
- removes untreated silverhalid crystals
also hardens the gelatine suspension
fixes crystals in position

Question 16

latent image fading

Answer 16

Silver atoms may revert to silver ions

• can happen if not processed straight away
• optical density may fall by 10-20 percent in 24 hours

Question 17

factors which affect radiographic image

Answer 17

1) contrast
- depends on subject and film
2) characteristics of the x ray beam
3) image geometry
4) image sharpness and resolution

Question 18

factors which affect subject contrast

Answer 18

1) different target/filter combinations
2) reducing the beam penetration/tube voltage
- how easy to get through substance
- harder beam goes through everything lose contrast
- too soft a beam, give lots of radiation dose to soft tissues close, will need even bigger to reach deeper tissues
3) using contract media
- can be used
- not common
- something into soft tissue so it can be imaged
4) use of scatter rejection grids or air gap
- allows scatter from patient to spread out before interacting with the film
- should get less scatter of what you don’t want

Question 19

film contrast

Answer 19

dependant on sensitivity on filter ray

narrow latitide, small change in dose big change in optical density

Question 20

what is fog and what does it lead to

Answer 20

blackening of film from natural processes

fog leads to a smaller ratio, therefore reduces the contrast by having great layer over image

Question 21

film speed

Answer 21

speed defined as change in optical density for change in exposure

Question 22

ideal characteristics of x ray beam

Answer 22

Ideal characteristics

• parallel
• produced from a point source to reduce penumbra
• sufficiently penetrating to pass through to a varying degree

Question 23

what is the beam held at and why

Answer 23

parallel to avoid distortion

Question 24

focal spot size

Answer 24

can’t have a small focal point as you need to dissipate the heat or a long time to do it slow (patient will move)

Question 25

image geometry

Answer 25

Object and film should be

• parallel
• perpendicular to the beam
• close together

Question 26

image sharpness types and resolution

Answer 26

1) Geometric unsharpness
- combination of penumbra and patient position
2) motion unsharpness
- blurred photo, worse with longer exposure photos more time to move
3) absorption unsharpness
- lots of tissue = lots of scatter
- reduces resolution on the film
4) screen unsharpness
- reduce resolution, good for dose
5) resolution of the film
- crystal size change to provide better or worse resolution at the cost of dose

Question 27

issues affecting image quality

Answer 27

dark
pale films
opaque film
marks on film

Question 28

how does computers radiography work

Answer 28

photo stimulate phosphors instead of filmq

Question 29

how does compuersied radiograph work steps

Answer 29

• hits atom in image plate
• frees an e
• jumps into a crystal defect and stays there for a short while
• red laser makes it drop back down to the level
• blue light given off
• detected
• bright white light then erases it
• reusable

Question 30

types of detectors that can be used in computerised

Answer 30

amorphous silicone

amorphous selenium

Question 31

quality of x rays grading

Answer 31

For film %
70 Excellent
20 acceptable
10 unacceptable