Main components of the tube headThe glass X-ray tube

The step-up transformerThe step-down transformerA surrounding lead shieldSurrounding oilAluminium filtration

The CollimatorThe spacer cone or beam-indicating device (BID)

Focal spot size and the principle of line focus

X-ray equipment, films and processing

X-ray generating equipmentImage receptorsProcessing facilities

Main components of the control panelThe main on/of switch and warning lightsThe timerAn exposure time selectorsWarning lights and audible signals

Circuitry and tube voltageTo generate the high potential difference (kV)

to accelerate the electrons across the X-ray tube via the step-up transformer

To provide the low –voltage current to heat the tube filament via the step-down transformer

Rectified circuitsDefinition-electrical device which converts

alternating current to direct current

Half-wave rectifiedSingle-phase, full-wave rectifiedThree-phase, full-wave rectifiedConstant potential

Diagrams of rectified circuits

Advantages of constant potential circuitry X-ray production per unit time is more

efficientMore high-energy, diagnostically useful

photons are produced per exposureFewer low energy, harmful photons are

producedShorter exposure times are possible

Image receptorsDirect –action

Indirect- action

Direct-action (non-screen) filmsUses

Sizes31/41 mm for periapicals22/35 mm for bitewings57/76 mm for occlusals

The film packet contentsOuter packetBlack paperLead foil

The radiographic filmA plastic base

A thin layer of adhesive

The emulsion on both sides of the base

A protective layer of clear gelatine

Indirect-action filmUses- extraoral views and intraoral vertex

occlusal radiograph

Construction- different emulsions are sensitive to blue, ultraviolet ,green or red light

It is essential that the correct combination of film and intensifying screens is used

For identification metal letters L or R are placed on the outside of the cassette

•Film speed –depends on size and number of crystals

•Film sensitivity- this is the reciprocal of the exposure required to produce an optical density of 1.0 above background fog

•Film latitude-this is a measure of the range of exposure that produces distinguishable differences in optical density• •Film contrast –the difference in optical density between two points on a film that have received different exposures

ability to differentiate between the different structures that are close together

Factors affecting resolution - image sharpness - size of crystals - contrast

Resolution- a measure of the radiograph’s

Intensifying screens

ActionCassettesFilm storageScreen maintenance

Processing Definition of processingProcessing theoryDiagram

Practical processing methodsManual

Automatic

Self-developing films

Requirements for manual processingAbsolute light-tightness

Adequate working space

Adequate ventilation

Adequate film storage facilities

Safelights

Processing equipments-tanks,

thermometers immersion, heater,

timer, film hangers

Adequate washing facilities

Manual processing cycleThe exposed film packet is unwrapped and the film clipped on to a hanger

The film is immersed in developer (at 20 degrees for 5 minutes) and agitated several times

Rinse the residual developer for 10 seconds

• Immerse the film in the fixer for 8- 10 minutes

• Wash the film under running water for 10- 20 min. to remove the residual fixer

•The film is dried in a dust – free atmosphere

Constituents of developer solutions and their functionsPhenidone- bring out the image

Hydroquinone- builds contrast

Sodium sulphite- reduces oxidation

Potassium carbonate- activates developing agents

•Benzotriazol- prevents fog

•Glutaraldehyde- hardens the emulsion

•Fungicide- prevents bacterial growth• •Buffer- maintains pH ( 7+)

•Water- solvent

Important points regarding development

The alkaline developer should be made up according to manufacturer’s instruction

Solutions should be changed every 10-14 days, irrespective of the number of films processed during that time

The recommended time is 5 minutes at 20 degrees

Fixer’s constituents and their functions

Ammonium thiosulphate- removes unsensitized crystals

Sodium sulphite- preservativeAluminium chloride- hardenerAcidic acid- maintains pHWater- solvent

Important notes regarding

fixing

Avoid contamination with developer and prepare according to manufacturer’s recommendations

Films should be fixed for double the clearing time (the time it takes to remove the unsensitized silver halide crystals)

•Films may be removed from the fixer after 2-4 minutes for wet reading but should be returned to the fixer to complete fixing

•Inadequate fixed films may appear greenish, yellow or milky and later brown

Automatic processing

Processing cycle- it is the same as for manual processing except that the rollers

squeeze off any excess developing solution before passing the film on to the fixer

Infection control measures

AdvantagesTime saving

No need for a darkroom

Standardized processing conditions

DisadvantagesStrict maintenance and regular cleaning are essential

Some models need to be plumbed in

Equipment is relatively expensive Smaller machine cannot process large extraoral films

Self-developing filmsAdvantages

- No darkroom or processing facilities are needed

- Time saving- the final radiograph is ready in about a minute

DisadvantagesPoor overall image qualityThe image deteriorates rapidly with time

There is no lead foil inside the film packet

The flexible film packet is difficult to use in positioning holders

Relatively expensive