Screen Film Radiography Flashcards
Radiographic film consist of two parts, what are they?
Base and Emulsion
What is the name of a film coated on both sides?
Double emulsion film
The base of consist of what type of structure?
Polyester
The principle function of gelatin?
to provide mechanical support for silver halide crystals by holding them in a uniform place.
98% of the emulsion is made up of?
silver bromide. The other 2% is made from silver iodide.
What is a sensitivity center?
Photoelectrons and silver ions are attracted to these centers to form a latent image.
The difference between high contrast versus low contrast films
high contrast emulsion contains smaller silver halide grains with uniform grain size. low contrast emulsion contain large grains with wider ranges of sizes.
To optimize speed, the screen films are double emulsion, why?
Primarily to increase efficiency by using the two screens to expose the film on both sides.
The purpose of a crossover control layer?
to reduce the blurring of an image and absorbs most of the crossover light
Difference between orthochromatic and panchromatic films?
orthochromatic responds to green-sensitive films while panchromatic films are sensitive to all visible light spectrum.
Red filter (light) are suitable for what?
for both green and blue sensitive films. Mainly used in dark rooms.
Improper handling and storage results in?
poor radiographs with artifacts
High amounts of heat and humidity will do what to the radiographs?
Increase fogging and lower contrast.
What happens when light is exposed to the emulsion before processing?
Low-levels of light will produce fogging. High-levels of light will produce artifacts.
How does excesses amount of scatter radiation affects the film?
Increases fog and reduces contrast.
True or False. After exposure no image can e observed on the film only a latent image exist.
True
Where is the greatest concentration of silver bromide and iodide found?
along the surface of the crystal
Where does the electron migrate after exposure is taken?
towards the sensitivity center. (e- becomes trapped and forms metallic silver.
What is the purpose of intensifying screen?
Coverts x-ray beam into visible light. Visible light interacts with the visible light to form the latent image.
What is the name of the layer closet to the radiographic film?
protective coating. About 10 to 20 um thick and designed to help the screen to become more resistant to damages from handling.
The layer within the intensifying screen responsible for emitting light?
Phosphor. Mostly made from gadolinium, lanthaunm, and yttrium.
Why is the phosphor layer made from rare earth metals?
Lowers patient dose, less thermal stress on the x-ray tube, and reduces shielding for ex-ray rooms.
What is the purpose of a reflective layer?
reflective light is intercepted and is redirected back towards the film
What is the base designed for?
Serves has support for the phosphor layer. Made out of polyester or cellulose triacetate
How does luminescence work?
Outer shell electron is excited x-ray beam, This causes e- to leave the shell creating a hole. When another e- fills that gap, a light photon is created.
What is the difference between fluorescence and phosphorescence?
a fluorescence material will glow while the phosphor is stimulated. a phosphorescence will continue to emit light after stimulation has ended.(Causes screen lag or afterglow)
A relative number that describes how efficiently x-rays and converted into light.
screen speed
The effecting factors of screen speed
it increases phosphor size, thickness of layer, concentration.
Increasing the temperature decreases the screen speed.
Name the phases for producing a manifested image.
wetting, developing, fixing, washing/drying.
the purpose of a developer?
to change the silver ions of exposed crystals into metallic silver.
what is the difference between reduction and oxidation?
reduction moves a e-. oxidation adds an e-
a reducing agent, produces shades of gray rapidly
Phenidone
a reducing agent, produces black tones slowly
Hydroquinone
What is the role of sodium carbonate?
controls the concentration of hydrogen ions (pH levels). helps with gelatin swelling.
Extremely corrosive and can burn skin
A chemical that restricts the developing agent to only silver halide crystals. Also controls the fogging of a image.
potassium bromide
What does a preservative do?
controls the oxidation of the developing agent by the air. Hydroquinone is sensitive to aerial oxidation. Uses sodium sulfite.
What controls the swelling and soften the emulsion?
a hardener agent. Glutaraldehyde
what removes the impurities from the developing agent?
Chelates
