Imaging on film

Question 1

The cassette

Answer 1

Designed to hold x-ray film and intensifying screens in close contact
Constructed of materials that are light-tight yet allow x-rays to pass
A lead blocker is located in the corner of the cassette
Avoid superimposing any vital areas of the patient over this blocker
The back of the cassette is constructed of heavier material and lined with lead to absorb backscatter which could cause film fog
The inside edges of the cassette are lined with felt or foam pressure pads to ensure close contact of the film and screens
A cassette should have sturdy construction, maintain screen-film contact and be user-friendly in the darkroom

Question 2

Imaging on film introduction

Answer 2

Radiographs are formed using light-sensitive film contained in a light proof container known as a cassette
Within the cassette are intensifying screens which are responsible for converting the x-ray radiation into visible light
Over 95% of the exposed film is due to light emitted from the intensifying screens
Less than 5 % is due to the ionization of x-rays
When the film is processed the latent image is converted to a visible image

Question 3

Cassette care

Answer 3

Dropping the cassette
Can result in loss of contact between screens and film
Leakage of fluids into the cassette
Can be prevented by placing cassette in a bag during messy situations
All cassettes should be numbered so easy to trace problem cassettes
Can use small number transfers or felt pen directly onto the screens at the corner or edge
The number will then appear white on the radiograph
The number must also be written on the outside of the cassette, for ease of tracing

Question 4

Quantum mottle

Answer 4

An artifact caused by increased screen speeds
A spotty appearance to the film
Due to less radiation used so not all phosphors are struck so not all phosphors fluoresce and light inconsistently reaches the film giving it a mottled look
Quantum mottle decreases as x-ray exposure is increased
Consequently, “fast” screen-film systems will have more quantum mottle than “slower” systems

Question 5

Xray film layers

Answer 5

Base – provides a flexible support
Adhesive Sub Coating – binds the emulsion to the base
Emulsion – consists of gelatin and silver halide micro crystals suspended and dispersed throughout layer
Super Coat – protective material prevents damage to emulsion layer

Question 6

Latent images

Answer 6

As the halide crystals absorb energy from light or x-rays a physical change takes place and a latent image is formed
A latent image is an invisible image on the x-ray film after it is exposed and before processing
After processing the latent image is converted to a visible image

Question 7

Screen films

Answer 7

Manufactured with silver crystals that are sensitive to fluorescent light emitted from intensifying screens
Requires less exposure of x-rays to produce quality image
Can be both green or blue sensitive or both

Question 8

Non-screen films

Answer 8

Exposed by direct action of radiation
There is not intensification of the x-ray beam so greater exposure are required
Because requires greater exposure it should be utilized only for areas where tissue thickness is minimal
Benefit – radiographs have better detail
Valuable when fine detail is required
Film is packaged in a light-tight envelope of heavy paper
Film is sensitive to pressure due to paper covering having little protective qualities

Question 9

Film care

Answer 9

Film handling and storage are of great importance
Film boxes should be stored on end so that the film is in a vertical position
If film is stored horizontal for extended period of time or if any pressure is placed on the film, the emulsion on each sheet may blend together
The result may be a “block” of x-ray films that are useless
Always handle film with respect
Gently, touching as little as possible
Film is easily compromised
Protect from light, radiation, and chemical contact

Question 10

Film fog

Answer 10

Can occur for several reasons based on improper storage of film
Store at room temp (better if able to place in a fridge) and low relative humidity
Excess temperature and humidity can soften the film emulsion causing film to stick together and decrease shelf life
Should not be stored near any source of radiation or chemical fumes
Do not keep extra films in the x-ray suite while making exposure
Do not keep stock supply in dark room – fumes from processor
Shelf life
Stock rotation to ensure using oldest product first
Supply companies also do this – so if you do not do a lot of radiography in your clinic ask for longest expire date possible (usually 18 months)