main components of the tube head the glass x-ray tube the step-up transformer the step-down...
TRANSCRIPT
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