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Main components of the tube head

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Presentation on theme: "Main components of the tube head"— Presentation transcript:

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




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