3. Radiographic Film Flashcards
conventional image
receptor
Radiographic Film
the medium that
records the image
Radiographic Film
Radiographic Film has 2 main parts:
base and emulsion
Radiographic Film is approximately
150-300µm
Radiographic Film layers
SEAF
- Supercoat
- Emulsion
- Adhesive layer
- Film base
primary purpose is to
provide a rigid structure
onto which the emulsion can be coated
Base
reduces eyestrain and fatigue, enhancing radiologists’ diagnostic
efficiency and accuracy
Dye
Radiographic Film: Base was originally made of
glass plates
replaced glass plates but
was flammable, resulted in severe hospital fires during the 1920s and early 1930s
Cellulose nitrate
similar to cellulose
nitrate but not as flammable;
“safety base”, was introduced in 1920
Cellulose triacetate
became base of choice in the early 1960s because of its superior dimensional stability
Polyester
Heart of the radiographic film
Emulsion
consists of a homogenous mixture of
gelatin and silver halide crystals; 3-5µm
Emulsion
is clear and porous and serves to
hold the crystals in place
Gelatin
Radiographic Film: Emulsion active ingredient
Silver halide crystal (98% Silver Bromide, Silver Iodide)
Tabular; 0.1 µm thick, 1µm in diameter
Emulsion
Sensitivity center (photoelectrons \+ silver ions) = latent image center
Silver sulfide
TYPES OF FILM
- Screen-Film
- Direct-Exposure Film
- Mammography Film
this type of film uses intensifying screens
Screen-Film
depends on size and
distribution of crystals
Contrast (Screen-Film)
small grains relatively uniform in size
High-contrast emulsion (Screen-Film)
large
grains that vary in sizes
Low-contrast emulsion (Screen-Film)
is the sensitivity of the screen-film combination to x-rays and light
Speed
speed is principally a function of the concentration and the total number of silver
halide crystals
Direct-exposure film
silver halide grain size,
shape, and concentration are the principal determinants of film speed
Screen-film
is the exposure of an emulsion caused by light from the opposite
radiographic intensifying screen
Crossover (Screen-film)
The crossover control layer has three critical
characteristics:
(1) It absorbs most of the crossover light,
(2) it does not diffuse into the emulsion but remains as a separate layer,
(3) it is completely removed during
processing
correctly matching the color sensitivity of the film to the color emission of the
intensifying screen
Spectral Matching
the color of light produced by a particular intensifying screen
Spectral emission
emit blue and blue-violet light
Calcium Tungstate
emit ultraviolet, blue,
green, and red
Rare Earth Screens
the color of light to which a particular film is most sensitive
Spectral Sensitivity
green sensitive film
Orthochromatic film
sensitive to entire visible
light spectrum
Panchromatic film
provide enough light to illuminate the darkroom
while ensuring that the film remains unexposed
Safelights
Safelights ____ bulb, no closer than ____ from work surfaces
15W,
3-4ft
amber safelights (550nm)
Blue sensitive film
red filter (600nm)
Green sensitive film and Blue sensitive film
manufactured for use without intensifying screens
Direct Exposure Film
thick emulsion with high concentration of silver halide crystals
Direct Exposure Film
single-emulsion film designed to be exposed with a single
intensifying screen
Mammography Film
Mammography Film uses
green-emitting terbium-doped gadolinium oxysulfide screens with green-sensitive film
Reflections at boundaries between film
emulsion, film base, intensifying screens, and cassette surfaces
halation
undesired marks or spurious images that
sometimes appear on processed radiographs
Artifacts
Heat and Humidity - stored at temperatures of _____
and a relative humidity of ____
55-75° F (13-24°C),
30-60%
The fog level for unprocessed film is approximately
2 μGya (0.2 mR)
In most x-ray film, the emulsion is coated on both sides; therefore, it is called
double-emulsion film
Between the emulsion and the base is a
thin coating of material called the _____, which
ensures uniform adhesion of the emulsion to the base.
adhesive layer
allows the emulsion and the base to
maintain proper contact and integrity during use and processing
adhesive layer
The emulsion is enclosed by a protective covering of gelatin called the
overcoat
protects the emulsion from scratches, pressure, and contamination
during handling, processing, and storage
overcoat
is the foundation of radiographic film
base
flexible and fracture resistant to allow easy handling but is rigid enough to be snapped into a view box
base
The base of radiographic film maintains its size and
shape during use and processing so that it does not contribute to image distortion. This property of the base
is known as _____
dimensional stability
is of uniform lucency and is nearly transparent to light
base
Radiologists used to refer to radiographs as
x-ray plates
is more resistant to
warping from age and is stronger than cellulose triacetate, permitting easier transport through automatic processors
Polyester
are thinner than triacetate bases (≈175 µm) but are just as strong.
Polyester
It is the material with which x-rays or light photons from
radiographic intensifying screens interact
Emulsion
The arrangement of atoms in the crystal is
cubic
It is clear, so it
transmits light, and it is sufficiently porous for
processing chemicals to penetrate to the crystals of silver
halide
Emulsion
Types of Film Used in Medical Imaging
- Intensifying screen
- Laser printing
- Copy or duplicating
- Dental
- Radiation monitoring
- Dry transfer
Intensifying screen emulsion
Two
Laser printing emulsion
Single with antihalation
backing
Copy or duplicating emulsion
Single with antihalation
backing
Dental emulsion
Two packed in sealed
envelope
Radiation monitoring emulsion
Two packed in sealed
envelope
Dry transfer emulsion
One
Blue or green sensitive
Intensifying screen
Matches laser used (≈630 nm)
Laser printing
Pre-exposed
Copy or duplicating
Has lead foil to reduce back scatter
Dental
One emulsion can be
sloughed off to increase OD scale
Radiation monitoring
Thermally sensitive
Dry transfer
General radiography
Intensifying screen
attached to
CT, MRI, ultrasonography,
and so on
Laser printing
Duplicating radiographs
Copy or duplicating
Dentistry
Dental
“Dry” printers
Dry transfer
SILVER HALIDE CRYSTAL FORMATION
AgNO3 + KBr → AgBr ↓(precipitated) + KNO3
The type of
imperfection thought to be responsible is a chemical contaminant, usually _____, which is introduced
by chemical sensitization into the crystal lattice, usually at or near the surface.
This contaminant has been given the name
silver sulfide,
sensitivity center
During exposure, ______ are attracted to these sensitivity centers, where they combine to form a latent image center of metallic
silver
photoelectrons and silver
ions
The size and concentration of silver halide crystals primarily affect
film speed
mammography, video recording, duplication, subtraction, cineradiography, and dental radiology
nonscreen film and special application film
The contrast of an IR is _____ to its exposure latitude, that is, the range of exposure techniques that produce an acceptable
image
inversely proportional
are more sensitive than
small-grain emulsions
Large-grain emulsions
This more efficient use of silver in the emulsion is called the _____ of the emulsion
covering power
Crossover is reduced by adding a dye to the
base; reduces crossover to near zero; this is called a
crossover control layer
Tabular grain emulsions reduce ____ because the covering power is increased, which relates not only to light absorption from the screen (which is increased) but also to light transmitted through the emulsion to cause crossover (which is reduced)
crossover
absorbing dye is an ____ coating
antihalation
Radiographic film should be stored at temperatures lower than approximately
20°C (68°F)
is the dull, uniform OD that appears if
the film has been inadvertently exposed to light, x-rays,
heat, or humidity
Film fog
the range of exposure techniques that produce an acceptable
image
exposure latitude
