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 Electronic sensors Dental Films DUPLICATING PhotoStimulable Phosphor Plate PSPP) ) Intraoral Charge-Coupled Device CCD)) Extraoral Direct exposure Screen P.A B.W Occl.

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 Stored energy X-ray photons absorbed Silver halide crystals Visible image 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 x-radiation. 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 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. Calcium tungestate; screen have phosphors crystals that emit blue light. 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 x-ray 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; The thickness of phosphor layer. The size of phosphor crystals. The presence or absence of light absorbing dyes within the screen. 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 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 photo-phosphor 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