CH19 Radiographici FIlm Flashcards
Basic radiographic film components:
Base and Emulsion Gelatin
Base
made of a blue tint dye and polyester. Coated with emulsion gelatin
Base requirements:
1) Good film contact 2) Flexible 3) Stable 4) Rigid 5) Uniform Lucent
Emulsion Coating contains:
Photosensitive silver halide crystals Bromides/Iodide/Chlorine
Uniform Lucent
Permits light to pass through with the use of light box.
Purpose of blue dye tint?
reduces eye strain and enhances contrast
Duplitized
Double coating of emulsion on each side
Duplicating film
copy of film, single emulsion
Supercoat
surrounds emulsion, layer of hard protective gelatin.
Supercoat prevents:
soft emulsions from from being physically or chemically abused. Damage can only occur through use of staples, paper clips, or guide shoes.
Panchromatic
Sensitive to all wavelengths.
Orthochromatic
Not sensitive to red.
Cube lattice:
Form in which silver halide crystals exist.
Sensitivity Peak
made of gold or silver, acts as an electrode to attract free silver ions (CUBE LATTICE/Crystals)
Direct of non-screen exposure
Enclosed in cardboard, w/o screens, use when need detail.
Single emulsion
Extremely fine grains, greater silver content, thicker emulsion layer, loaded face up.
Emulsion side appears:
Dull
Non emulsion side apears:
shiny
Film is sensitive to:
Age, heat, humidity, light, radiation, handling
Film should be stored at:
20 deg C (68F), 60-70F
Film constantly absorbes:
Photons of both heat and light
When storing film:
it should be on end (upright) in a cool dry place.
Intensifying Screens:
Used to amplify the incoming xray beam
Benefits of an intensifying screen:
Reducing radiation dose to the patients, produced large quantities of light photons.
Contruction of intensifying screen:
Base, Reflective layer, Phosphor layer, Protective coat, mounted in pairs.
Base made of:
Polyester
Reflective layer
base material not transparent, creates latent image, reflects towards film
Phosphor layer
Active layer of screen, absorbes light.
Protective coat
protects phosphor layer from abrasions and stains
Phosphor requirements
High atomic number, conversion efficiency, sepctral emission/spectral matching, Luminescence, phosphorenscence.
High phosphor atomic number allows
increased probability of an incident photon interaction
Conversion efficiency means
the ability of the phosphors to emit as much light as possible
Spectral emission
precise wavelength emitted
Luminescence
ability of material to emit light in response to excitation
Phosphorenscence
Continued emission of light by a phosphor after the exposure has ended.
Screen should be replaced how often?
Every 5-7 years
Types of phosphors
Zinc sulfide, Barium lead sulfate, *Calcium Tungstate (CaWO4)
Hybrid rare earth screens provide
greater absorbtion, atomic number 51-71, known as rare earth because of it’s difficulty to isolate
Hybrid rare earth screens can be made of either:
Gadolinium, Lanthanum, Yttrium
Quantum Mottle
Uneven density, insuffiecient amount of x-rays. More common in high speed film and digital.
Screen characteristics
Same as film 1)Resolution 2)Speed 3)Contrast 4)Lattitude(not error latitude)
Screen resolution is
the ability to produce an accurate image.
Screen resolution is controlled by
1)size of crystals 2)thickness of the layer 3)Concentration of crystals
Smaller Crystal results in
Thinner layer, many more crystals, slower speed, more exposure, and more detail.
Larger Crystals results in:
Thickness layer is larger, less crystals, faster speeds, less exposure, less detail.
Speed
is determined by the same factors that effect resolution.
Higher kVp does what to speed?
Increases speed.
Temperature increase will have what effect on speed?
The speed will slow down.
Screen speed characteristics
1)Intensification factors 2)Descriptive factors 3)Relative (Speed # ex. RS100 RS200)
Spectral matching
Film and screens respond to certain wavelengths, that must match spectrally.
Rare earth color is
green
Calcium Tungstate color is
purple
Cassettes purpose is
to create a portable, light proof case for the film.
Cassette requirements are:
1) Rigid 2) Radiolucent 3)Lead->to absorb backscatter
