Transcript X-ray equipment, films and processing X

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)
Focal spot size and the principle of line
focus
X-ray equipment, films and
processing
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X-ray generating equipment
Image receptors
Processing facilities
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
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
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
Diagrams of rectified circuits
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
Image receptors
 Direct –action
 Indirect- action
Direct-action (non-screen) films
 Uses
 Sizes
 31/41 mm for periapicals
 22/35 mm for bitewings
 57/76 mm for occlusals
The film packet contents
 Outer packet
 Black paper
 Lead foil
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
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
•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
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
Intensifying screens
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Action
Cassettes
Film storage
Screen maintenance
Processing
 Definition of processing
 Processing theory
 Diagram
Practical processing methods
 Manual
 Automatic
 Self-developing films
Requirements for manual processing
 Absolute 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 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
• 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 functions
 Phenidone- 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
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•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
Fixer’s constituents and their functions
 Ammonium thiosulphate- removes
unsensitized crystals
 Sodium sulphite- preservative
 Aluminium chloride- hardener
 Acidic acid- maintains pH
 Water- 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
Advantages
 Time saving
 No need for a darkroom
 Standardized processing conditions
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
Self-developing films
 Advantages
- No darkroom or processing facilities
are needed
- Time saving- the final radiograph is
ready in about a minute
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