Factors relating to the production of radiograph
A. Factors relating to the radiation beam. B. Factors relating to the object. C. Factors relating to the X-ray film.A. Factors relating to the radiation beam.1.exposure time:- it’s the interval during which X- rays are being produced exposure time is directly related to the total photon production thus increase exposure time cause increase in the quantity of X-radiation that’s why exposure time has direct effect on film density.
2. Milliamperage:- its related to amount of electricity pass through the filament circuit. So it's directly control the rates of X- ray photon production thus it has direct effect on film density. 3. Kilovoltage:- kV it refers to the potential difference between cathode and anode in the X- ray tube the higher kVp the greater is the potential difference and the greaten is the energy of X- ray photons.
4. Tube–film distance:-this distance consist of (tube– object distance) and (object–film distance), now the tube – film distance affect the intensity of radiation (according to inverse square law), while the tube – film distance affect the exposure time directly so the distance proportional directly with the exposure time but the distance proportion inversely with the intensity of radiation also the distance affect the dose of radiation because decrease the tube – film distance make the X- ray beam more diverge behind the skin area and more tissue is irradiated. While increase the distance make the beam less diverge and reduce the amount of tissue irradiated.
Effect of collimation:-a. reduce the amount of tissue irradiated b. Minimize the production of secondary radiation fog. 7. Filtration:- effect of filtration is the absorption of long wave length x- ray photons that have low penetrating power (can't penetrate the hard classified tissue). The result of filtration of X- ray beam is hardened beam (more short more length photon with high penetrated power) so increase the half – value layer also increase filtration affect the contrast and density but in different way the contrast is decreased (long scale) like the effect of increase kV. While the density is decreased because when filtration increase the result is the absorption of not only long wave length photons but even some of short wave length photons so the number of X- ray photons or the quantity or radiation is reduced so the density is reduced.8. Equipment efficiency:- dental X- ray machine differ in construction and efficiency so the quality and quantity of X- ray beam vary from machine to another.
B – Factors relating to the object:- The object is basically and x- ray absorbing medium so 2 points important about the object during exposure to x- ray:- 1. Thickness of the object. 2. Density of the object. 1.Thick object required more radiation to make a radiographic image so its often advisable to increase kV or mA and or exposure time in order to increase the amount of X- ray photons. 2.Dense object:- density refers to weight per unit volume of the object in dental radiography enamel of the tooth has highest density of all body tissues increase the density of the object increase its ability to absorb X-radiation. So hard tissue like enamel absorb great amount of radiation when compared with absorption of soft tissue like pulp because of object density.
C – Factors relating to the x- ray film:-1. Reduction of secondary radiation:-secondary radiation include scattered, stray leakage or any other radiation that not belong to primary X- ray secondary radiation is un desirable because it reaches all parts of the film and produces film fog minimizing this radiation done by:- 1. Using as small beam of radiation as possible. 2. Proper collimation. 3. Using a sheet of lead foil behind the film in the film packet.
4.In extra and intra oral film there is grid which is a sheet of absorbing material (lead) in strips shape this grid placed between the object and the film and it absorb this secondary radiation.
2. Film and film storage:- X- ray film must stored in light tight containers because the Ag Br Crystals in the emulsion are sensitive to light as well as to X- ray. Also film must not stored in place where we have excessive temperature or humidity or stray radiation that’s why it placed in a lead – lined box and we should used it before the expiration. 3. Intensifying screen 4. Proper film processing * Fog:- is the unwanted film density (blackening) and thus reduce radiographic contrast.