Oral radiology Radiographic film
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Radiographic film (X-ray film)
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Radiographic film is an image receptor, the term "image" refer to picture or reflection of an object and "receptor" refer to anything that responds to a stimulus.
It is a type of photographic film, in which an image is formed by the exit radiation exposing the film.
Composition of the Radiographic film:
The film is composed of 2 principal components namely the base& emulsion.
Base:
0.2 (or 0.007) mm thick & made up of clear, transparent cellulose tri acetate or Cellulose nitrate. Cellulose acetate is used because it is less inflammable. Recently polyesters [polyethylene teraphthalate] are used. The base should be flexible for easy handling{manipulation}.
Emulsion:
Consists of homogenous mixture of gelatin & silver halide crystals. The gelatin is made from cattle bone. The gelatin is clear so that it will transmit light & sufficiently porous to allow the processing chemicals to penetrate it & reaches the silver halide crystals fast without affecting the strength.
A protective coating of gelatin is added over the emulsion[super coat].
Silver halide crystals namely the Silver bromide& Silver iodide are embedded in the gelatin matrix.
Also there are : a) Lead foil: a thin sheet placed behind of the emulsion (film). Lead foil protect the film from secondary or scattered radiation which cause fog, gives rigidity of the packet, embossed pattern on lead foil enable to understand the cause of under-exposure, and prevent the amount of residual radiation that pass through the film to continue into patient's tissue. b) The film is encased in a protective black paper wrapper, black paper covers the film & lead foil, it shields the film from light, damage by fingers and prevent contamination from saliva. c) Outer plastic wrapper: The films are wrapped in packets of white, pebbled, moisture-resistant paper or polyvinyl wrap and is sealed to prevent the ingress of saliva and light.
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Oral radiology Radiographic film
There is a raised dot [Embossed dot] is seen on one corner of the film packet, which helps :
1.
to orient the film towards the x-ray beam.
2.
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3.
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Types of Xray Films according to sensitivity :
1.Direct exposure or non-screen films.[Intra-oral films: Also called wrapped or packet film, this type is sensitive primarily to x-ray photons.
2.Indirect exposure or screen films.[Extra-oral films in combination with
intensifying screens in a cassette]: this type is sensitive primarily to light photons. its mainly of 2 types: a) Blue light sensitive: these film contain calcium tungstate in the screen. b) Green light sensitive: these film contain rare earth elements.
Types of Xray Films according to using : a) Intraoral films : we can divided them to three categories :
1.
Periapical films: used for taking of periapical radiographs, it records the outline, positions, and dimension of the teeth, its available in different size e.g. (1.0 or 1.1 or 1.2):
Size 0: for children (22 × 35 mm).
Size 1: for anterior teeth adult (24 × 40 mm).
Size 2: for posterior teeth adult (31 × 41 mm).
Film packets are available in 25, 100, 150 film per container.
2.
Bitewing films: these are manufactured with bite tabs/wings attached to the film packet. its used for detection and evaluation of proximal caries and alveolar bone loss in both dental arches. its available in different size e.g. (2.0 or 2.1 or 2.2 or 2.3):
Size 0: for children posterior teeth (22 × 35 mm).
Size 1: for mixed dentition, posterior teeth (24 × 40 mm).
Size 2: for posterior teeth adult (31 × 41 mm).
Size 3: for posterior teeth adult (narrower and longer), (27 × 54 mm).
3.
Occlusal films: its larger than periapical film, used to take occlusal projections to detect the lesions. They record image of entire arch on one film, it is usually positioned in the occlusal plane and patient occludes on it.
Size : 57×76 mm
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Oral radiology Radiographic film b) Extraoral films : used for extraoral radiography and these film may be in combination with intensifying screen (screen films) or not
(non screen films).
Sizes : lateral oblique film: 5 × 7inches
Panoramic film : 6 × 12 or 5 × 12 inches.
Cephalometric film: 8 × 10 inches.
Skull radiography: 10 × 12 or 6.5 × 8.5 inches. c) Duplicating film : used when dublication is required, its sigle emulsion film.
Types of Xray Films according to speed of the film :
Speed: mean the amount of radiation required to produce the radiograph of adequate density.
1.
Slow speed films :
These types contain small size of grains of silver halide. This film gives better definition but requires more exposure time as these films are single-emulsion sided film. They are denoted by A,B and
C speed.
2.
Fast speed films :
These types contain larger grains size of silver halide. These films are double-emulsion sided. they require less exposure time. They are denoted by D (ultra speed), E (ekta speed), E+ (ekta plus speed) and F (ultra ekta speed).
3.
Hyperspeed G: this is 800 speed film.
Factors affecting film speed:
1.
Size of crystal: increased size more speed.
2.
Shap of grains: more surface area more speed.
3.
Thickness of emulsion: more thickness more speed.
4.
Radiosensitive dyes: using of this dyes increase the speed less radiation.
Film storage:
Film storage should be:
1.
In cool and dry place: temperature (50-70 F), humidity (30%-50%).
2.
Away from ionizing radiation.
3.
Away from chemicals fumes including mercury and mercury containing compounds.
4.
Pressure artifacts: film boxes should place on their edges.
5.
Light proof area: for opened boxes of screen films.
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Oral radiology Radiographic film
6.
Sequence of using the films: oldest film should be used at first then the newest.
7.
Handling : should be carfully to avoid film's scratches by finger nails.
Film holding device:
It is a device that used to position the introral film in the mouth and maintain the film in its position during exposure, this device is required with both paralleling technique as well as bisecting angle technique.
Advantages:
1.
Placement of the film.
2.
Retention of the film.
3.
Reduction of exposure to the patient.
4.
Avoiding partial image artifact (cone cut).
Disadvantage:
1.
Placement of the film beyond the apical area.
2.
Cann't be used with abnormal condition: e.g. presence of tori.
3.
Patient discomfort.
4.
Checking the position of film before exposure.
1.
Density of the film (D):
Optical density or photographic density is aterm used to describe the degree of blackening of the film and is measured by densitometer.
In diagnostic radiology, the range of density is 0.3 to 2.
The film which transmits 1/10 th
of light through it has density of 1,
(D –log (1/1/10 th
) = log 10 =1.
D = 0 (100% of light is transmitted).
D = 1 (10% of light is transmitted).
D = 2 (1% of light is transmitted).
Factors affect density of films:
1) Factors in relation with x ray machine a) Kilovoltage peak: when kVp ↑ the density will ↑ (darker film), how?
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Oral radiology Radiographic film b) Milliamperage: when mA ↑ the density will ↑ (darker film), how? c) Exposure time: when ET ↑ the density will ↑ (darker film), how? d) Source to film distance: when this distance ↑ the density will ↓ , how? e) Filtration: if added filter is used the density will ↓ . f) Grid: if a grid is used the density will ↓ .
2) Factors in relation with image receptor a) X ray film type: b) Intensifying screen:
3) Factors in relation with object a) Type of material: ? b) Thickness of material: ? c) Intrernal structure of object: ? d) Shape of object: ?
4) Factors in relation with processing of the film. a) Developing of the film b) fixing of the film
2.
Contrast:
It is the difference in optical density between two points on a film that have received different exposures. Minimum contrast can be detected visually under best condition is about 0.02.
High contrast film (short scale contrast): when many black and white areas and few shade of grey or density level. It is useful in detection and progression o dental caries. It is occur in the range of 65 kVp.
low contrast film (long scale contrast): when many shade of grey instead of black and white areas. It is useful in detection of periodontal and periapical diseases. It is occur in the range of 70-75 kVp.
Factors affect on contrast:
1) Factors in relation with patient: a) Tissue thickness b) Tissue density c) Atomic number
2) Factors in relation with x-ray machine. a) kVp: when kVp ↑ → low contrast film. b) Penetrating power c) Exposure rate: when ET ↑ → low contrast film.
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Oral radiology Radiographic film
3) Factors in relation with image receptor (film): a) density b) speed c) type (screen film or non screen film). d) Emulsion (double or single).
4) Factors in relation with processing of the film. a) Processing of the film: i) over-developing or under-developing → low contrast film. ii) ↑ temperature →↑ contrast b) Scatter radiaton: → low contrast film. c) Fog: → low contrast film.
3.
Sharpness:
It define as the ability of x ray to define outline of an object, it is measured in line pairs per millimeter that can be seen on an imaging device.
Unsharpness: it is refer to blurring of the boundaries.
Factors affect on sharpness:
1.
Focal spot size: ↑ F.S. size → ↓ sharpness.
2.
Silver halides crystals: ↑ crystal size → ↓ sharpness.
3.
Moement: → ↓ sharpness.
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