Main components of the tube head

1. Main components of the tube head The glass X-ray tubeThe step-up transformerThe step-down transformerA surrounding lead shieldSurrounding oilAluminium 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 equipmentImage receptorsProcessing 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

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

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

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

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. 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

16. 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

17. 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

18. Intensifying screens • Action • Cassettes • Film storage • Screen maintenance

19. Processing Definition of processing Processing theory Diagram

20. Practical processing methods Manual Automatic Self-developing films

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

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

23. 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

24. 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

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

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

27. 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

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

29. 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)

30. 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

31. 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

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

33. 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

34. Self-developing films Advantages - No darkroom or processing facilities are needed - Time saving- the final radiograph is ready in about a minute

35. 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