1. Main components of the tube head
The glass X-ray tube The step-up transformer The step-down transformer A surrounding lead shield Surrounding oil Aluminium filtration The Collimator The spacer cone or beam-indicating device (BID)

2. Focal spot size and the principle of line focus

3. X-ray equipment, films and processing
X-ray generating equipment Image receptors Processing facilities

4. Main components of the control panel
The main on/of switch and warning lights
The timer
An exposure time selectors
Warning lights and audible signals
Electronic timer- dead man switch
Dead man switch
Selectors- in sec; anatomical area

5. Circuitry and tube voltage
To 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
Diagr.5.7

6. Rectified circuits
Definition-electrical device which converts alternating current to direct current
Half-wave rectified
Single-phase, full-wave rectified
Three-phase, full-wave rectified
Constant potential

7. Diagrams of rectified circuits

8. Advantages of constant potential circuitry
X-ray production per unit time is more efficient
More high-energy, diagnostically useful photons are produced per exposure
Fewer low energy, harmful photons are produced
Shorter exposure times are possible

9. Image receptors Direct –action Indirect- action
Direct-action –sensitive primarily to X-rays. Indirect- to light

10. Direct-action (non-screen) films
Uses
Sizes
31/41 mm for periapicals
22/35 mm for bitewings
57/76 mm for occlusals

12. The film packet contents
Outer packet
Black paper
Lead foil

13. The radiographic film A plastic base A thin layer of adhesive
The emulsion on both sides of the base
A protective layer of clear gelatine
Base- support for the emulsion,but does not contribute to the final image
Adhesive- fixes the emulsion to the base
Emulsion- consists of silver halide (usually bromide) crystals. X-rays sensitized them to metal silver and bromide gas.
Protective layer of clear gelatine to shield the emulsion from mechanical damage

14. Indirect-action film
Uses- 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

15. Characteristics of radiographic film
Optical density-degree of film blackening measured by densitometer. In diagnostic radiology the range of optical densities is 0,25-2,5.
Characteristic curve- variation in optical density with different exposures

16. 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

17. 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

18. Resolution- a measure of the radiograph’s
ability to differentiate between the different structures that are close together
Factors affecting resolution
- image sharpness
- size of crystals
- contrast

19. Intensifying screens
Action
Cassettes
Film storage
Screen maintenance

20. Processing Definition of processing Processing theory Diagram
Processing- the sequence of events required to convert the invisible latent image,,contained in the sensitized film emulsion, into the visible, permanent radiographic image

21. Practical processing methods
Manual
Automatic
Self-developing films

22. Requirements for manual processing
Absolute light-tightness
Adequate working space
Adequate ventilation
Adequate film storage facilities

23. Safelights
Processing equipments-tanks,
thermometers immersion, heater,
timer, film hangers
Adequate washing facilities

24. Manual processing cycle
The 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

25. Immerse the film in the fixer for 8- 10 minutes
Wash the film under running water for min. to remove the residual fixer
The film is dried in a dust – free atmosphere

26. Constituents of developer solutions and their functions
Phenidone- bring out the image
Hydroquinone- builds contrast
Sodium sulphite- reduces oxidation
Potassium carbonate- activates developing agents

27. Benzotriazol- prevents fog
Glutaraldehyde- hardens the emulsion
Fungicide- prevents bacterial growth
Buffer- maintains pH ( 7+)
Water- solvent

28. Important points regarding development
The alkaline developer should be made up according to manufacturer’s instruction
Solutions should be changed every days, irrespective of the number of films processed during that time
The recommended time is 5 minutes at 20 degrees

29. Fixer’s constituents and their functions
Ammonium thiosulphate- removes unsensitized crystals
Sodium sulphite- preservative
Aluminium chloride- hardener
Acidic acid- maintains pH
Water- solvent

30. 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)

31. 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

32. 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
No need for dark room
Controlled conditions
Automatic solutions replenishment
Disadvantages-strict maintenance (dirty rollers-marks); plumbing, expensive

33. Advantages Time saving No need for a darkroom
Standardized processing conditions

34. Disadvantages Strict maintenance and regular cleaning are essential
Some models need to be plumbed in
Equipment is relatively expensive
Smaller machine cannot process large extraoral films

35. Self-developing films
Advantages
- No darkroom or processing facilities are needed
- Time saving- the final radiograph is ready in about a minute
No processing facilities, time saving ( 1 min)
Disadvantages-poor image quality, expensive difficult to use with instruments

36. Disadvantages Poor overall image quality
The 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