Lecture 6: image recording & processing

Question 1

What does an X-ray film pack consist of?

Answer 1

1- outer cover: water and light proof
2- black card: primary function is to add physical strength, so card doesn’t bend in patients mouth. Secondary function is to absorb light.
3- lead foil: to maintain a clear image by preventing any ‘backscatter’ from other tissues (tongue, teeth) affecting the image
4- film with photographic emulsion: this produces the image.

Question 2

What does the x-ray film consist of?

Answer 2

• polyester base (maintains shape and form) this has a slight colour dye to it
• on each side of the base is a subbing layer (fixes emulsion to the base)
• active emulsion

Question 3

in dental x-ray film, what is the active emulsion?

Answer 3

silver-bromide

Question 4

What causes differences in absorption?

Answer 4

• high kV (low attenuation due to less scatter)
• density
• atomic number
• thickness

Question 5

Why is it called an emulsion?

Answer 5

because the silver-bromide molecules are suspended in gelatine

Question 6

What does the film be dupitized mean?

Why is this done?

Answer 6

• it means the active emulsion is on both sides of the base

- this arrangement allows a diagnostic level of density to be achieved at half the dose that would otherwise be needed

Question 7

What are imaging steps involved in producing radiographs?

Answer 7

1- latent image formation
2- developing the latent image
3- fixing the image

Question 8

what is a latent image?

Answer 8

It is an image that already exists, but is invisible.

It needs to be developed.

Question 9

How is a latent image formed?

Answer 9

• Upon interaction with an x-ray the silver or bromine atom of the molecule is ionised and this weakens the bonds between silver and bromine causing them to dissociate.
• The number of molecules dissociating is proportional to the number of x-ray photons hitting that part of the emulsion.

Question 10

What would happen when photons pass through the pulp cavity?

Answer 10

A lot of photons would pass through and hit the silver-bromide crystals causing many of the molecules to dissociate

Question 11

What would happen when photons pass through enamel?

Answer 11

Few photons would pass through and hit the silver-bromide crystals causing no molecules to dissociate

Question 12

How is an image developed?

Answer 12

• The crystals in the film emulsion are surrounded by a negative charge that repels the electrons of the developer
• After exposure, the crystals with dissociated molecules have a defect in this negative charge shield and allows electrons from the developer to enter.
• The developer enters exposed crystals and donates electrons.
• These electrons exert a force of attraction on the positive charged silver atoms, causing them to clump together and this darkens the exposed area.

Question 13

What is used as a developer for x-ray images?

Answer 13

a reducing agent (donates electrons to the material)

Question 14

What 2 functions does the fixer have?

Answer 14

Functions:
1-The fixer dissolves the unexposed silver bromide crystals so no further exposure can take place: image is made permanent
2- The fixer hardens the emulsion to protect it and prevent scratching during storage

-after fixing, the image is washed and dried

Question 15

Why is an image fixed?

Answer 15

-To make the image permanent and the protect it from damage

Question 16

What are the 6 stages in full processing of radiographs?

Answer 16

1-  Development
2- Rinse
3- Fixing
4- Rinse
5- Wash
6- Dry

Question 17

in manual tanks, how long does the processing take?

Answer 17

over an hour

Question 18

EXAM QUESTION:

in manual tanks, what are the labels of each process starting at film handling?

Answer 18

1-film handling
2-developer
3-fixer
4-wash
5-dryer

Question 19

What would a yellow stain on the film be caused by?

Answer 19

• fixer left in the emulsion

- it breaks down and deposits sulphur crystals, due to inadequate washing

Question 20

why would automatic processing be faster?

Answer 20

• the chemicals are more concentrated and faster acting

- the process takes place at higher temperatures

Question 21

What is a disadvantage of automatic processing? (high temperature and higher concentration?

Answer 21

it will reduce the contrast of the image

Question 22

What are intensifying screens?

Answer 22

fluoroscopic materials that convert high energy x-ray photons into an increased number of light photons

Question 23

What is the purpose of the intensifying screen?

Answer 23

to reduce the radiation dose to the patient

Question 24

What would cause the film to be fine in the morning and progressively get darker throughout the day?

Answer 24

thermostat is broken and the film overheats

Question 25

What would cause the film to be fine in the morning and progressively get lighter throughout the day?

Answer 25

heater is broken and the film doesn’t get warm enough

Question 26

What are the 2 types of Digital Image Recording?

Answer 26

1- Direct (DDR: Direct Digital Recording)

2- Indirect (CDR: Computer Digital Radiography)

Question 27

What does direct digital imaging use?

Answer 27

charge coupled devices (wired system)

This is totally instant

Question 28

What does indirect digital imaging use?

Answer 28

photo phosphor plates (need to process the plate)

Question 29

What 3 types of recording medium are there?

Answer 29

1- phosphoplates
2- film (best image quality)
3- direct image radiography, using sensors

Question 30

What is the process of digital imaging?

Answer 30

1- analysis: collect numerical information based on the image
2- enhancement: improve appearance of image
3- encoding:

Question 31

How does the digital system produce an image?

Answer 31

the digital system reduces the analogue image to average values in the form of pixels (less information as it leaves out subtle differences in shade)

Question 32

How does indirect imaging work?

Answer 32

-uses phosphor plates

1- phosphorescence absorbs radiation and the electrons are raised in energy but they are delayed in falling back down to their original energy level
2- the release of the lower energy photons is controlled by external forces

Question 33

What is phosphorescence?

Answer 33

is the absorption of high energy photons followed by the later release of lower energy photons.

Question 34

How does direct imaging work?

Answer 34

1- x-ray photons passing through phosphor plate excite electrons (raised to higher energy level)
2- The electrons are held in a suspended state within ‘traps’ known as energy anomalies
3- the image is stored as a pattern of raised energy electrons
4- The laser light scans and allows the electrons to drop back down.
5-The energy released is detected and the values recorded.

Question 35

What are the advantages of film imaging?

Answer 35

• records a wider range of grey scales

- contains more image information

Question 36

What are the disadvantages of film imaging?

Answer 36

• vulnerable to extreme environments
• processing faults and artefacts are common
• COSHH regulations

Question 37

What are the advantages of digital imaging?

Answer 37

-image manipulation (density and contrast)
-ease of image transfer
-good for teaching purposes
no COSHH regulations

Question 38

What are the disadvantages of digital imaging?

Answer 38

• sensors/plates are expensive

- sensors/plates easily damaged

Question 39

What does film processor quality assurance check for?

Answer 39

1- fall in fluid levels
2- fall in temperature
3-exhaustion of chemicals