Aspirin Resistance 2003 08 13

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1 : Dental x-ray film processing By Prof. Dr. Omar Khashaba
2 : It is a collective title given to a series of operations carried out in a dark room which affect clinical changes in the exposed photograph film, thus making the image visible and ensuring its permanence. Fundamentally processing consists of immersing the exposed film first in developing solution then in a fixing solution with interference rinsing an washing with subsequent procedures.
3 : Steps: Immersing the exposed film in developing solution. Rinsing. Fixation. Washing. Dryness. Mounting
4 : Each step has to be performed in a definite sequence and in a standardized manner. Both solution (developing. and fixing) should be in a high degree of purity and uniformity and be maintained at an optimal temperature when used. It is essential that the film remains in each solution for the appropriate time necessary for chemical change to take place. The exposed film should be freed from its paper wrapping or released from its cassette in a white-light room both artificial and day light.
5 : I. Development It is a process by which the latent image becomes visible after exposure of the film to radiation. When the film is exposed to radiation, the crystals of silver bromide which is suspended in the emulsion of the film undergoes physical changes. If the film - after exposure - is immersed in a suitable development solution the bromide is removed from the exposed silver bromide crystals. Small particles of black metallic silver are left behind which form the visible image
6 : As the developing solution contains a reducing agent the process of development is in fact one of chemical reduction - parts of the film emulsion which are not obscured by an object during exposure to radiation receive the full effective x-ray beam and. provided that the film does not re main in the development for much longer than the recommended time Only these silver bromide crystals are actually reduced to metallic silver and therefore these areas of the film appears black due to large number of black silver particles left deposited.
7 : The other areas of the film that correspond to a dense object are unaffected by x-ray as most of the radiation is absorbed in the object and does not reach the film. These unexposed and unaffected particles are still acted upon. by the developing solution, but in this case the process of reduction is very slow and minimal. The undeveloped and unreduced silver bromide particles are subsequently removed from the film when the latter Is placed in a fixing solution and are seen in the film as clear transparent areas conforming the outline of the object.
8 : An object composed of varying density distributed through out its volume allows x-ray to pass through more or less inverse proportion to density. The undermined silver nitrate crystals will be affected according to the amount of radiation they receive. In this way the radiographic film will show varying degrees from clear white, shades from grey to dark areas and is an image of internal structure of the object.
9 : Composition of Developing Solution Hydroquinone: This agent is concerned with the production of high contrast in radiograph. Metol: It is concerned with production of good details. Sodium Carbonate: Is added to the solution to maintain and provide the degree of alkalinity in which the developing agent can function. It is also called the accelerator because it speeds up the development process.
10 : Potassium Bromides Has a restraining action. i.e. It slows down the reducing action of the developing solution and prevent the formation of excessive fogue. Sodium Sulfite: Inhibits the tendency of the developing agents to combine with oxygen dissolved in H2O Therefore it acts as a preservative and keeps the solution in usable condition, because oxidation of the developing agent will form colored substance which would stain the film. Water: Is used as a solvent of the chemicals and as a medium in which they can react with the silver bromide with the film emulsion.
11 : II. Rinsing The film after being removed from the developer and before being immersed in the fixer it should be rinsed in water for few seconds and if possible this should be with running water.
12 : III. Fixation The developing solution removes the bromide from the exposed silver bromide crystals without substantially affecting the unexposed. crystals. The undeveloped silver bromide will now be acted upon by the fixing solution. Sodium thiosulphate is a chemical agent which will remove the silver bromide without adverse effect on the film. It reacts with the undeveloped Ag. Bromide and converts it into a soluble substance which can subsequently be washed off the film.
13 : In order to stop any further action by the developer it is necessary to use an acid etching solution. Acetic acid is commonly used to neutralize any developer which is carried over by the film. However, acetic acid will decompose sodium thiosulphate and liberate sulpha unless sodium sulphite is also present in the solution. Sodium sulphite therefore prevents deterioration of the solution.
14 : The developer and fixing solution both containing high concentration of dissolving salts which prevents excessive swelling of the gelatin on the film emulsion as the washing water contains no such concentrations. The gelatin would swell and soften when transferred. from the fixer to water. Therefore potassium alum is included in the fixer to harden the gelatin and prevents excessive swelling during washing. As in the case of developer water is used as a solvent for the chemicals in the fixing solution.
15 : IV. Washing It is not advisable to switch on the white light until the film has been in the fixer for about 30 seconds. After fixation the film should be washed in a tank of cold running water for at least 20 minutes to remove fixer and products of fixation. If these substances are left in the emulsion, the fixer will, attack the silver image and certain byproducts of fixation will decompose to give a yellow stain
16 : V. Drying When the film has been thoroughly washed the water should be allowed to drain off, hangs and if necessary the hanger should be shaken carefully to dislodge residual H2O. The film should not be touched before it becomes completely dried otherwise the image may be damaged.
17 : VI. Mounting After drying the radiograph should be mounted in such a way that can be studied under proper illumination. Each film must be mounted correctly and inscribed with the patient’s name and date of expo sure for identification and indexing.
18 : Thank you


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