Image Receptors & Accessories / orthodontic courses by Indian dental academy

OMR, CODS, DVG

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

www.indiandentalacademy.com

OMR, CODS, DVG

Image Receptors:Initially glass plates were used By 1900: celluloid base film 1913: Moisture proof dental packet 1919: Kodak ‘Regular’ film 1924: Kodak ‘Radiatized’ film 1940: Kodak ‘Ultraspeed’ film

1952: Selenium plates in Xeroradiography1981: Kodak ‘Ektaspeed’ film1989: CCDs developed for dental radiography1994: Kodak ‘Ektaspeed Plus’ film


IMAGE RECEPTORS

OMR, CODS, DVG

Types:1. X-ray Films2. Fluorescent Screens3. Selenium Plates4. CCDs


IMAGE RECEPTORS

• Direct exposure films ( also called as non-screen films ) are used in intra- oral radiography• Indirect exposure films ( also called as screen films ) are used in extra- oral radiography in combination

with intensifying screensOMR, CODS, DVG

X-ray Films:


IMAGE RECEPTORS

Composition of an X-ray Film

OMR, CODS, DVG

Supercoat

Emulsion

Base


IMAGE RECEPTORSComposition of an X-ray Film

OMR, CODS, DVG

• Supercoat: a thin layer of polyester or gelatin covers both surfaces of the film to protect the emulsion from scratching

• Emulsion: coated on both sides of the base~ made up of gelatin matrix in which silver halide ( mainly AgBr2 ) crystals are suspended~ crystals are 1 / 0.7 micrometer in thickness

• Base:~ made up of polyethylene terephthalate ( polyester )~ 0.2 mm in thickness~ translucent, chemically inert~ supports emulsion


IMAGE RECEPTORSUses & Dimensions of Intra-oral X-

ray Films

OMR, CODS, DVG

• Periapical Projection: to record teeth and alveolar bone

3 sizes ~ ‘0’ : 22 x 35 mm ( for children )

~ ‘1’ : 24 x 40 mm ( for anterior teeth )

~ ‘2’ : 32 x 41 mm ( for adults )• Bitewing Projection: to record crown portion of maxillary and mandibular teeth in one image

~ Size ‘0’ and ‘1’ for children~ Size ‘2’ for adults~ Size ‘3’ ( 27 x 54 mm )• Occlusal Projection: to record larger areas of

maxilla or mandible~ Size ‘4’ ( 57 x 76 mm )www.indiandentalacademy.com

IMAGE RECEPTORSUses & Dimensions of Intra-oral X-

ray Films

OMR, CODS, DVG

Size ‘4’ (57 x 76 mm)

Size ‘0’ (22 x 35 mm)

Size ‘2’ (32 x 41 mm)


IMAGE RECEPTORSContents of an X-ray Film Packet

OMR, CODS, DVGwww.indiandentalacademy.com

IMAGE RECEPTORSContents of an X-ray Film Packet

OMR, CODS, DVG

† Plastic cover† Black paper† Lead foil† Direct exposure film

Protects the film from moisture and

light

Protects the film exposure to light

1. Protects tissues on the other side of the film from radiation2. Prevents backscatter radiation from reaching the film3. Gives sufficient stiffness to the film packet

Captures the image pattern and forms a

latent image


IMAGE RECEPTORS

• Direct exposure films ( also called as non-screen films ) are used in intra- oral radiography• Indirect exposure films ( also called as screen films ) are used in extra- oral radiography in combination

with intensifying screensOMR, CODS, DVG

X-ray Films:¤ These films are similar in their composition to the non-screen films with the exception that certain impurities are added to make the emulsion more sensitive to light.¤ The latent image is formed by the light emitted from the intensifying screens.


ACCESSORIES

OMR, CODS, DVG

1. Intensifying screens2. Film holders, cassettes & stands3. Grids


ACCESSORIES

OMR, CODS, DVG

Intensifying screens - Composition

Protective layer

Phosphor layer

Reflectinglayer

Base

~ made up of polyester~ about 0.25 mm thick~ provides mechanical support to the screen

~ made up of titanium dioxide~ about 0.025 mm thick~ reflects the light from the phosphor layer back to the film

~ made up of phosphor crystals suspended in plastic~ phosphor materials used are : calcium tungstate or rare earth elements like # terbium activated gadolinium oxysulfide # thulium activated lanthanum oxybromide~ emits light when exposed to x-radiation~ exposure to an x-ray photon results in emission of several light photons~ help in reducing radiation dose in extra-oral radiography

~ made up of polyester~ about 0.8 microns thick~ protects the phosphor layer and provides a surface that may be cleaned


ACCESSORIES

OMR, CODS, DVG

Intensifying screens - Functioning


ACCESSORIES

OMR, CODS, DVG

Intensifying screens - FunctioningThe x-ray film, therefore, needs to kept very close to the intensifying screen. In fact, it is sandwiched between a pair of intensifying

screens inside a metallic cassette.

Magnification and Unsharpness of Image


ACCESSORIES

OMR, CODS, DVG

Film Holders, Cassettes & StandsFilm Holders hold the film in patient’s mouth, and maintain its position during exposure. They may also aid in alignment of x-ray beam with the x-ray film.

XCP (extension cone paralleling) Instrumentswww.indiandentalacademy.com

ACCESSORIES

OMR, CODS, DVG

Film Holders, Cassettes & StandsFilm Holders :


ACCESSORIES

OMR, CODS, DVG


Snap-A-Ray Instrumentwww.indiandentalacademy.com

ACCESSORIES

OMR, CODS, DVG


Artery forcepsor needle holder


ACCESSORIES

OMR, CODS, DVG

Film Holders, Cassettes & StandsCassettes carry a non-screen film between a pair of intensifying screens. They protect the film from light and moisture, and also maintain a tight contact between the film and the intensifying screens.


ACCESSORIES

OMR, CODS, DVG

Film Holders, Cassettes & StandsCassette stands are used in extra-oral radiography for holding and maintaining the cassette in correct position with respect to the patient.


ACCESSORIES

OMR, CODS, DVG

GridsA grid is composed of alternate strips of a radiopaque material (usually lead) and strips of a radiolucent material (usually plastic). Purpose of grid is to prevent the secondary radiation coming from the tissues from reaching the film, thus improving the image quality.

Grid

FilmUSEFUL

RADIATION

Secondary

radiation


ACCESSORIES

OMR, CODS, DVG

GridsTypes of grids: • stationary and mobile (Bucky, Potter-Bucky diaphragm)• parallel, focussed

Grid ratio: ratio of grid thickness to the width of radiolucent spacer. Higher the grid ratio better is the image quality. Generally a grid ratio of 8-10 is satisfactory. Use of grids requires doubling of exposure. Hence, grids should be used only when sufficient improvement in image quality is expected.

As large amounts of secondary radiation is produced by the maxillo-facial structures grids are useful in extra-oral radiography. In intra-oral radiography, grids can neither be used nor is there a need to use them.


IMAGE RECEPTORS & ACCESSORIES

OMR, CODS, DVG

1. Intensifying screens2. Film holders, cassettes & stands3. Grids

Types:1. X-ray Films2. Fluorescent Screens3. Selenium Plates4. CCDs


IMAGE RECEPTORSCharge-Coupled Device ( CCD )

OMR, CODS, DVG

A CCD is made of an array of photodiodes (devices that conduct electricity when light or x-rays strike them) on top of a semiconductor.

‘CCD’ is a sensitive electronic device that stores packets of information as

electric charge.


Each element, called a ‘pixel’,

is 20-60 microns in size.

(A human hair is about 60 microns

in diameter!)



serial output register

output amplifier

Computer hardware

& software

Display Storage Printer








OMR, CODS, DVG

High image quality at considerably less radiation dose as compared to film radiography. Image is dynamic and can be altered digitally. No processing required; therefore environment friendly. Image is available instantly. No processing errors. No loss of image over a period of time. Image duplication is very easy. Telemedicine.

Advantages:



OMR, CODS, DVG

Limitations: Very high initial cost. Sensor is bulkier compared to an x-ray film making it difficult to place in some parts of the mouth and in children.


DIRECTING THE X-RAY BEAMTO THE OBJECT

INTERACTION OF X-RAYS WITH MATTER

DIFFERENTIAL ABSORPTION OF THE X-RAY BEAM

EMERGENCE OF AN

INVISIBLE IMAGE

PATTERN

CAPTURE OF THE INVISIBLE IMAGE PATTERN ON AN IMAGE RECEPTOR

‘Latent Image’

Processing

Latent image is formed when tiny specks of metallic silver are deposited in those silver bromide crystals that are exposed to radiation. This image is invisible.



Thank you

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Image Receptors & Accessories / orthodontic courses by Indian dental academy