Film Imaging Flashcards
(27 cards)
What is image receptor made from?
Film and screen
What is the film made from?
A protective transparent coat
Emulsion
Adhesive layer
Base
What is the film emulsion made from?
Silve halide
90% silver bromide, 10% silver iodide
What is the adhesive layer and base used for?
Adhesive layer sticks the emulsion to the base
The base is used for structure
What is the screen made from?
Protective layer - transparent
Phosphor
Reflective layer
Base plate
What is phosphor used for in screen?
To convert x-ray into light
What is use of reflective layer?
Reflect light back towards film?
What interactions are present in image receptor?
X-ray interact w/ phosphor layer - converts energy into photos
Photons emitted all directs = activation Silver halide = area blackening
What does x-ray speed depend on?
Thickness of phosphor layer - the thicker that phosphor more chance of x-ray interaction
Crystal size - larger = more blackening = worse resolution = increased speed
How is resolution affected by speed?
Increased speed = reduced resolution
What is purpose of light absorbing dyes?
Prevent the light from spreading too far - increases resolution but decrease speed
What is latent image formation?
X-ray hits crystal giving e- in bromide enough energy to escape = sensitivity speck
E- is negative and attract mobile Ag+ = Ag atom = silver deposits which are more sensitive to developed = blackening
What is developer?
Alkali which acts as a reducing agent
Converts Ag+ –> Ag by addition of electron
Process begins at sensitivity speck
What happens if image developed for too long?
AgBr crystal converted to silver = black film
What does washing do?
Stops developer
What if fixing?
An acid which removes unreacted silver halide
What is purpose of final wash?
Fixed solution still slightly sensitive to light - must be remove or will react producing brown stain
What has happened if image too dark?
Overexposed or developed/ fogging due to storage
What is image too pale - what happened?
Underexposed or underdeveloped
What has happened if opaque film?
Inadequate fixing or final wash
What happens with age of film or inappropriate storage?
Background fog
Fog blackening can happen from background radiation
What happens at higher x-ray beam (dose)
Lower pt dose
D films are slow
E/F films are faster
What is the ideal film geometry?
Parallel to avoid stretch or magnification
Detector close to tooth to reduce spread
Why can’t focal spot be too small?
Generate too much heat
But if too large = spread = blur
