Download IMAGE RECEPTORS

Image Receptors
Image Receptors
The term image refers to a picture or likeness
of an object.
• The term receptor refers to something that
responds to a stimulus (light ,X-ray…).
• In dental radiography, after the x-ray beam
passes through the teeth & adjacent structures, it
reaches the x-ray film. The dental x-ray film
serves as a recording medium or image receptor.
Image Receptors
Dental Films
Electronic sensors
DUPLICATING
Intraoral
Extraoral
Screen
P.A
B.W
Occl.
Charge-Coupled
)Device CCD)
Direct exposure
PhotoStimulable
Phosphor Plate
) PSPP)
Intraoral X-Ray Film
Which is placed inside the mouth during x-ray
exposure.
Intraoral Film Packet:
Dental x- ray film packets have four basic
components:1. Outer Package Wrapper.
2. Lead Foil Sheet.
3. Black paper Film Wrapper.
4.X-RAY Film.
1. Outer Package Wrapper:
Is a soft vinyl or paper envelope, to protect the film
from exposure to light and saliva.
It has two sides:
Tube Side: which face the teeth and the tube
head , and contained raised dot.
Label Side: It has a flap that is used to open the
film packet before processing.
A circle which corresponds the raised dot on the
film.
The statement “opposite side toward tube”.
The manufacturer’s name.
The film speed.
2. Lead Foil Sheet:
A single piece of lead foil ,behind the film wrapper.
 It prevents most of the secondary radiation,
originating in the tissues of the patient behind
the film from reaching the film, that results in
film fog.
 It absorbs x-rays that have passed through the
object and film thus reduces exposure of the
tissues behind the film.
3. Paper Film Wrapper ( black paper):
Protect the film and shields the film from light.
4.X-RAY Film
Film Composition:
The x-ray film used in dentistry has four basic
components:
FILM BASE.
ADHESIVE LAYER.
FILM EMULSION .
PROTECTIVE LAYER.
FILM BASE:
► Is
a flexible piece of polyester plastic. The film
base is transparent & exhibits a slight blue tint
that is used to emphasize contrast & enhance
image quality.
► To withstand heat, moisture, and chemical
exposure.
► To provide a stable support and strength for
emulsion.
ADHESIVE LAYER
► Is
an adhesive material that covers both sides
of the film base.
► It is applied to attach the emulsion to the base.
FILM EMULSION







Is a coating attached to both sides of the film
base by the adhesive layer to give the film
greater sensitivity to x-radiation.
The emulsion is a homogeneous mixture of
gelatin and silver halide crystals.
The gelatin is used to suspend silver halide
crystals over the film base.
A halide is a chemical compound that is sensitive
to radiation or light. Halides: Sliver bromide
(AgBr) form 80-90% & silver iodide (AgI) form
10% of entire silver halide crystals.
The silver halide crystals absorb radiation during
x-ray exposure and store energy from the
radiation.
During processing, the gelatin serves to absorb
the processing solutions & allow the chemicals to
react with the silver halide crystal.
Protective Layer:
Is a thin, transparent coating
placed over the emulsion.
To protect the emulsion surface
from manipulation, mechanical
and processing damage.
Types of Dental X- Ray Film:
Three types of x-ray film may be used in dental
radiography:
Introral film:  Periapical (examine teeth,
supporting bone).
 Bite-wing (upper, lower teeth
crown).
 Occlusal film (large area of
max.and mand.).
Extra oral film:
Screen film Direct exposure film.
Duplicating film.
INTRAORAL FILM SIZES:
Intraoral film size: Intraoral radiographic
film is available in several size & speeds.
The most common sizes are designated;
• Size-0: pedo -type.
• Size-1: adult anterior type.
• Size-2: adult posterior type (standard film).
• Size-3: bitewing type (0, 1, 2, & 3).
• Size-4: occlusal type.
INTRAORAL FILM SPEED
Is the amount of radiation required to produce a
radiograph of standard density. Film speed, or
sensitivity, is determined by the following:
 The size of the silver halide crystals.
 The thickness of the emulsion.
 The presence of special radiosensitive dyes.
An alphabetical classification system 
ranging from A speed (the slowest) to F speed
(the fastest). Only D-speed film and E-speed
film are used for interior radiography.
INTRAORAL FILM PACKAGING:
• To protect from light and
moisture.
• Plastic trays cardboard boxes.
Boxes of intraoral film are
labeled with the type of film,
speed, size, number of films
and the film expiration date.
LATENT IMAGE FORMATION
X-ray photons
absorbed
Silver halide
crystals
Visible image
Stored
energy
processing
Latent image
EXTRAORAL FILM
• Extraoral films are used to examine large
areas of the skull or jaws e.g. panoramic &
cephalometric films.
• Extraoral film used in dental radiography
is available in 5×7 inch & 8×10 inch
sizes, as well as the panoramic 5×12inch
& 6×12inch sizes.
EXTRAORAL FILM TYPES
• Screen film: that requires the use of a screen
for exposure. Screen film is sensitive to
fluorescent light rather than direct exposure to xradiation. Some screen film are sensitive to blue
light, whereas others are sensitive to the green
light.
A screen film is placed between two special
intensifying screens in a cassette.
• Direct exposure film: The film is exposed
directly to the x-ray, which require more
exposure time than screen type film.
Intensifying Screen: is a device that
transfers x-ray to visible light. These
screens intensify the effect of x-rays on
the film, therefore less radiation is required
to expose the film & the patient is
exposing to less radiation.
Intensifying Screen
• Composition:
• Base: its made of a polyester & give
the mechanical support to the screen.
• Reflecting layer: is a coating of
white titanium dioxide applied to the base
to reflect stray light back to x-ray film.
• Phosphorus layer; it contains either
fluorescent or phosphor crystals suspended in
the gelatin material.
1. Calcium tungestate; screen have phosphors
crystals that emit blue light.
2. Rare-earth screens; have phosphors that are not
commonly found in the earth & emit green light.
The use of rare earth screens means less
exposure to x-radiation for patient.
• Thin protective coating; is durable
enough to withstand repeat insertion & removal
of film from the cassette while protecting the
underlying phosphor layer.
Action: Two intensifying screens are used;
one in front of the film & the other at the back of
the film:
• The front screen absorbs the low energy x-ray
photons.
• The back screen absorbs the high energy
photons.
• The two screens are stopping the transmitted xray beam.
• Each photon will produce many light photons
which will affect a large area of the film, thus the
amount of radiation to the patient is reduced..
Fluorescent Materials
Three main phosphor materials are used in
intensifying screens;
• Calcium tungestate (CaWO4).
• Rare earth phosphors including
gadolinium & lanthanum.
• Yttrium (a non-rare earth phosphor but
having similar properties).
Calcium Tungestate Screens:
the main points can be summarized as
following;
• The speed of these screens depends upon;
1. The thickness of phosphor layer.
2. The size of phosphor crystals.
3. The presence or absence of light absorbing dyes
within the screen.
4. The conversion efficiency of crystals.
• The faster the screen, the lower the radiation
dose to the patient but the less the detail of
the final image.
• All calcium tungestate screens emit blue
light & must be used with blue-light sensitive
monochromatic radiographic film.
Rare Earth & Related Screens:
these new phosphors have been introduced
to increase screen speeds even more,
without excessive loss of image detail.
• The term rare earth is used because it is
difficult & expensive to separate these
elements from earth & from each other,
not because the elements are scarce.
Rare earth & related screens are app. 5
times faster than the tungestate screens. It
is important to use the appropriate films
with their correctly matched screens.
Cassette
1.
2.
3.
4.
5.
6.
Cassettes are available in a variety sizes that
corresponding to the film size & screens. The cassette
is may be flexible or rigid.
A rigid cassette is more expensive, last longer, &
protects the screen from the damage.
Both types of cassettes must be light tight in order to
protect the film from the exposure to the light & to hold
the screens in the perfect contact with extraoral film,
because lack of contact resulted in a loss of image
sharpness.
The front cover of the cassette is made of plastic to
permit the passage of x-ray beam.
The back cover is constructed from heavy metal to
reduce scattered radiation.
The cassette must be marked to orient the finished
radiograph; a metal L or R are attached to the front
cover of cassette to indicate the patient sides.
DUPLICATING FILM:
Its
• a type of photographic film that is
used to make an identical copy of an
Intraoral or Extraoral radiograph.
A duplicating radiograph is used for;
1.Patient is referred to a specialist.
2.For insurance claim.
3.As teaching aids.
Film Duplication Procedure
Duplicating film is used only in a darkroom
and is not exposed to x-rays.
1.Place radiograph to be duplicated on the
light screen of the film duplicator, & block
out extraneous light.
2. Place the film to be duplicated against
the emulsion side of the duplicating film.
3. Secure duplicator lid (to prevent blurring
of the image, good contact must be
maintained between the radiograph & the
duplicating film).
4. Activate the light source to expose the
duplicating film (longer exposure to the
light lead to lighter copy i.e. opposite to the
x-ray film).
5. Process the duplicating film in
conventional x-ray processing
solution.
6. Label the processed duplicating
radiograph with patient's name & date
of exposure & label to indicate the
patient's right or left sides.
Film Storage and Protection
1- The film must be stored away from sources of
radiation, in temperatures of 50 to 70 degrees
Fahrenheit and with a relative humidity level of
30 t0 50%.
2- To prevent film fog, lead-lined or radiation–
resistant film dispensers and storage boxes are
ideal.
3- Dental film should always be used before the
expiration date on the label.
DIGITAL RADIOGRAPHY
The x-rays interact with x-ray film to 
make a radiograph.
An electronic image also results from 
an electron interaction (receptors in pt.
mouth) with x-ray and processed by a
computer. (digital image)
DIGITAL RADIOGRAPHY
There are two basic mechanisms of digital radiography:
1. Direct digital imaging: involves the use of a sensor that
is directly wired to the computer, such as CCD.
2. Indirect digital imaging involve the use of photophosphor plates that are activated using x-ray ,then
scanned in special devices that read the image. The
image then displayed on the computer monitor, such
as PSPP.
Direct digital imaging
Indirect digital imaging