Latent Image formation & Dark room Chemistry.pptx

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1. Latent Image formation & Dark room Chemistry . Presented by:- Dr. Stutee Beriwal Pg 1 st year

2. Contents 1) Introduction X-ray film composition Latent image formation on the film . 2) Dark Room Chemistry Dark room requirements Processing equipment's 3) Film processing steps . 4) Film processing solutions . 5) Different methods of processing.

3. Introduction Film processing refers to series of steps carried out in the dark room, that produce a visible image on dental radiograph. Aims of processing -To convert the latent (invisible) image on the film into a visible, permanent radiographic image. -To preserve the visible image so that it is permanent and does not disappear from the dental radiograph.

4. The film emulsion is a suspension of silver bromide and silver iodide crystals precipitated in gelatin and layered on a thin sheet of transparent base. Interstitial free silver ions and presence of iodide atoms causes physical distortion in the regular rectangular crystal. The silver halide crystals are chemically sensitized by the presence of Sulphur compounds and these are called s ensitivity/latent image sites.

5. Latent Image When the radiographic film is exposed to the information carrying beam of photons exiting an object, the photosensitive silver halide crystals in the film emulsion interact with these photons and are chemically changed. These chemically altered crystals are said to constitute the latent (invisible) image of the film. These chemical changes in the crystals increase the liability of crystals to the chemical action of the developing process that converts the latent image into visible image. The production of latent image is the first step of the photochemical process.

6. FORMATION OF THE LATENT IMAGE A.   A silver bromide crystal in the emulsion of an x-ray film contains mostly silver and bromide ions in a crystal lattice. In unexposed silver halide crystal, the bromine ions usually occupy the surface of the crystal and the silver ions occupy the center of the crystal. There are also free interstitial silver ions and areas of trace chemicals like Sulphur that form sensitivity sites (electron traps)

7. B: Exposure of the crystal to photons in an x-ray beam results in the release of electrons, usually by interaction of the photon with a bromide ion. The recoil electrons have sufficient kinetic energy to move about in the crystal. These electrons gets trapped at the sensitivity site, imparting a negative charge to this region. The bromine on losing electron becomes positive charged and moves into the gelatin of the Xray film base. Later t he bromine dissolves in the developer on processing .

8. C,   Free interstitial silver ions (with a positive charge) are attracted to the negatively charged sensitivity site.  D,  When the silver ions reach the sensitivity site, they acquire an electron and become neutral silver atoms. These aggregate of silver atoms at the latent image site compromises the latent image. It is the metallic silver at each latent image site that catalyzes the development of the halide crystal and renders it sensitive to development and image formation.

9. The primary actions of the processing solutions is to convert the crystals with latent image sites into black metallic grain the can be visualized and also to remove the unexposed silver bromide crystals. A) Grey areas- Latent image produced by exposure. B) Black (metallic silver)- Partial development begins in exposed grains. C) Development completed D) Fixation completed- Unexposed silver grains are removed by fixation.

10. The Dark Room Dark room is a place where the necessary handling and processing of films can be carried out safely and efficiently, without the hazard of producing ‘film fog’ by accidental exposure to light or x-rays. The primary function of the dark room is to provide a completely darkened environment where the X-ray film can be handled and processed to produce a diagnostic image in an efficient, precise, and standardized procedure. Since the processing operations are carried out in near total darkness, every piece of equipment must be in a specific place. Near total darkness means Safe illumination. It must exclude all outside light and provide safe artificial light.

11. Dark room construction : General lay out Darkroom illumination Darkroom equipment's and its arrangement

12. 1. General Lay Out Size: Group practice/Institution- 16 to 20 square feet The size will vary depending upon: Volume of radiographs processed. Number of persons using the dark room. Type of processing equipment used. (processing tanks or automatic processor) The space required for the film storage. Adequate counter area at least 3 feet away from the processing tank should be available where the films can be unwrapped prior to processing. This area should be absolutely clean, dry and free of processing chemicals, water , dust and debris.

13. The temperature and humidity level of the darkroom must be controlled to prevent film damage. A room temperature of 70 degree F ( 21 degree Celsius) and humidity levels between 50 to 70% is recommended to be maintained. The dark room plumbing must include both hot and cold running water along with mixing valves to adjust the water temperature in the processing tanks. Must include a utility sink with running water. Miscellaneous: Waste basket for disposal of all film wrappings. requirements X-ray view box.

14. Dark room construction : General lay out Darkroom illumination Darkroom equipment's and its arrangement

15. 2 Illumination As term dark room suggests the room must be completely dark and must exclude all visible light- which is termed as Light proof . It should not have any light leaks . Re commended: Use of both white light and safe light. ( White light illumination is required during preparation of solutions and cleaning tanks ) Fluorescent lights should not be used due to the short after glow that may fog the first few films opened after the light is turned off.

16. S hould be of low intensity , with a relatively long wave length of 600 nm and above (orange – red) which does not rapidly affect open film , but permit one to see enough of working area . Arrangement of safe light filters should be such that , three zones of illumination are provided . Dimmest zone : Area where the cassettes are loaded and intraoral films opened. Medium zone : areas where films are developed and processed. Bright zone : area where the films are washed and placed in the drier. This can be accomplished by placing one safe light above the working area and another on the wall behind the processing tanks. Precaution: Excessive exposure of film to safe light can cause film fog . Following 3 factors must therefore be considered. 1) Type of filter 2) Intensity of illumination 3) Time of exposure.

17. Type of filter X –ray films have highest sensitivity in the blue green region of the spectrum and are less sensitive to light in yellow and red region . Hence safe light are safe when made up of amber or red filters. Commonly used filters are: Moralite filter(cannot be used for screen films) . Wratten series 6B filters Red GBX – 2 safe light filter

18. Intensity of illumination Intensity should be adjusted to minimize fogging effect of prolonged exposure Inverse square law: Intensity is inversely proportional to square of the distance. Thus correct intensity can be obtained by adjusting either the distance of the bulb or wattage or both. Recommended: The wattage of the bulb should be 7 ½ to 15 watts. The distance of the safe light above the work area should be 4 feet.

19. Time of exposure Film handling under a safe light should be limited to about 5 minutes because film emulsion shows some sensitivity to safelight due t o prolonged exposure .

20. Tests for checking Unsafe Illumination Film fogging can either be due to Use of inappropriate safe light filters Excessive exposure of safe li ght filters Stray light.

21. Coin test / penny test : Used to evaluate fogging due to inappropriate safe lighting conditions. Shut all lights and put on safe lights . Open the film packet and place the base film in the place where the films are usually unwrapped . Place a coin on the film and leave it in this position for approximately the time required to unwrap and mount a full mouth set of radiographs , usually 5 minutes . Develop the test film as usual . Inference : If the processed film shows an outline of the penny, the film is being fogged by inappropriate safe light conditions.

22. Dark room construction : General lay out Darkroom illumination Darkroom equipment's and its arrangement

23. 3. Processing Equipment Manual processing technique Automatic film processor. Manual processing / Hand or Tank processing: Simplest and most efficient procedure with accurate control. Processing tank Thermometer Timer Film hanger Stirring rod/ Stirring paddle Plastic Apron

24. 1) Processing tank : contains 2 parts ( 1 master tank and 2 insert tanks ). Master tank : Size 8 ´´× 10´´ . The master tank suspends both insert tanks and is filled with circulating water. It helps to maintain the temperature of the processing solutions. An overflow pipe is used to control the water level in master tank . Master tank should have a cover – to reduce oxidation , evaporation and contamination of processing solution . Insert tanks : Should have a capacity to hold 1 gallon of developer or fixer . 2 in number ( 1 for developer and 1 for fixer ) D eveloper tank is placed on left and fixer on right side of master tank. W ater in master tank separates the 2 insert tanks . All the three tanks are made up of stainless steel . Stainless steel (316 s.s with 2.3% Molybdenum) is preferred as I t does not react with processing solutions I t accommodates more rapidly to change in temperature . E asy to clean . Tanks that are soldered should not be used as reaction of the solution with the solder metals can cause chemical fogging.

25. 2) Thermometer : Clipped on the side of the tank or left free floating in the tank. - To check and maintain the temperature of the developing and fixing solution . 3) Timer : - To control the time of development and fixation . 4) Film hangers ( film racks or processing racks ) : Is a device equipped with clips , used to hold film during processing . Made of stainless steel. 5) Stirring rod / paddle : Used to agitate the processing solutions – to mix the chemicals and equalize the temperature of the solutions. Made up of plastic or glass. 6) Plastic apron : Used to protect clothing during the processing of films.

26. Processing Solution . Film processing solutions obtained in the following forms: Powder Ready to use liquid Liquid concentrate Developer solution -contains 4 basic ingredients 1) Developing/ Reducing agents . 2) Preservative . 3) Activator 4) Restrainer 5)Hardener 6) Fungicide 7)Buffer 8) Solven t

27. Developer (reducing agent) Developing agent : Primary function: Conduction of electrons from developing agents to exposed silver halide crystals and to reduce the exposed silver ions to solid grains of metallic silver. Metol Phenidone (1 – phenyl – 3 – pyrozolidone ) Phenidone serves as first electron donor that converts silver ions to metallic silver at latent image sites. This electron transfer generates the oxidized form of phenidone . 2) Hydroquinone (Para dihydroxy benzene) Hydroquinone provides electron to reduce the oxidized phenidone to its original active state so that it can continue to reduce silver halide grains to metallic silver. Responsible for production of high contrast in radiograph. 3) Elon ( mono methyl – para – aminophenol sulphate) Elon helps to develop the shadow areas or shades of gray on the film and brings out the details.

28. Preservative : Its an antioxidant, usually sodium sulphite . Action: T his inhibits the tendency of the developing agent to combine with the oxygen dissolved in water or in the air. Thus preserve the solution in usable condition for several weeks. Oxidation of the developing agents forms colored substance which would stain the film and add to the film fog. Activator/ Accelerator : Alkaline compounds (activators ) such as sodium or potassium carbonate . ( gives it a soapy texture) Action: Keeps the developer at alkaline pH, usually around 10 – 11 , hence active. The activator also cause the gelatin to swell so that the developing agents can diffuse more rapidly into the emulsion. Excessive alkalinity- Rapid reduction of even unexposed silver bromide crystals, can produce fog. Excessive gelatin swelling which may result in blister/frill.

29. Restrainer : Bromide usually potassium bromide or benzotriazole. Action: It slows down the reduction action of the developing agents They usually depress the reduction of both exposed and unexposed crystals; however they are much more effective in depressing the reduction of unexposed crystals . Thus the restrainer act as anti for agents and increases contrast . Hardener : - Glutaraldehyde (added especially in automatic processing) Actions: T o prevent the emulsion from softening and sticking to rollers. Fungicide : - To prevent bacterial growth . Solvent : - Distilled water is used

30. Developer Replenisher : In normal course of film processing, phenidone and hydroquinone is consumed , and bromide ions and other by products are released into solution. Developer also become inactivated by exposure to oxygen – “Seasoned “ solution. The recommended amount to be added daily is 8 ounces of fresh developer per gallon of developing solutions – for development of an average of 30 periapical and 5 panoramic films per day.

31. Fixing solution Primary function: To dissolve and remove the underdeveloped silver halide crystals from the emulsion. Secondary function: To harden and shrink the film emulsion . Fixing solution consists of : 1)Clearing agent ( fixing agent) 2) Acidifier 3) Preservative 4) Hardener

32. Clearing agent ( fixing agent) : Made up of ammonium/sodium thiosulfate (hypo) . Action: Ammonium thiosulfate chemically reacts with the undeveloped silver bromide and converts it into a stable water soluble complex which are be subsequently washed out of the film. Preservative : Sodium sulfite is the preservative in the fixing solution , as it is in developer. Action: It prevents the oxidation of thiosulfate clearing agent , which is unstable in acidic environment. It binds with any colored oxidized developer carried over into the fixing solution, thus prevents staining of the film. Acidifier : Fixing solution contains acetic acid buffer system ( pH 4 to 4.5). Action: To keep the fixer acidic pH constant. Acidic pH is required to promote good diffusion of thiosulfate into the emulsion and of silver thiosulphate complex out of the emulsion. T he acid fixing solution also inactivates any carry over developing agents in the film emulsion , hence blocking continued development of any unexposed crystals while the film is in fixing tank.

33.   Hardener : Hardening agent most often used are aluminum sulfate / aluminum chloride/ potassium alum. Action: Aluminum complexes with the gelatin ( by chelating process) during fixing and prevents damage to the gelatin during subsequent handling. Hardeners also reduce swelling of the emulsion during final wash. This lessens mechanical damage to the emulsion and limits water absorption , thus shortening drying time . Solvent : Water is used

34. Chemical Reduction of Radiographs An over exposed or over developed film will be too dark for convenient viewing , owing to excessive deposit of silver which obscures the image details . Photographic reducer contains an oxidizing agent potassium ferricyanide which oxidizes silver to silver ferrocyanide, which is in turn dissolved by the solution of sodium thiosulphate . This is known as Farmer’s Reducer - which consists of two solutions Solution A : Potassium ferricyanide 75 gms . Water to make 1000 ml Solution B : Sodium thiosulphate crystals 240 gms . Water to make 1000 ml Method: Take 1 part of solution A and 4 parts of solution B, and 27 parts of water . - Immerse the radiograph in mixed solution and watch carefully , when the film has sufficiently reduced , it should be washed in running water for 30 minutes.

35. Chemical intensification of radiographs  Radiograph may be too light because of underexposure , under development or both . Instead of repeating the radiograph , chemical intensification can be done . Most of the intensification methods act by converting silver which forms the image into a compound which is more opaque, more colored or of a different physical form . Commercially available intensifying solutions are : - In – 4 chromium intensifier In -5 silver intensifier Copper iodide intensifier solution XR- 10 intensifying solution Liner toner solution Low density radiograph is immersed in intensifying solution for a period of 3-8 minutes or depending upon the density increase required .

36. Different Methods of Chemical Processing Manual method – Time temperature method Modified time temperature method Visual method Rapid processing method 2. Automatic method 3. Monobath method 4. Day light method 5. Self developing films

37. Manual Film processing Consists of 5 steps : Development Rinsing Fixing Washing Drying . 

38. Development : Film is placed in a chemical known as developer solution for a specific amount of time at specific temperature. Development is a chemical process that amplifies the latent image by a factor of millions to form a visible silver pattern. -The basic reaction is reduction (addition of an electron) of the silver ion, which changes it to black metallic silver. Ag+ + electron Ag (Silver ion in (electron from developer) (silver atoms) crystal containing the latent image) Actions: Developer distinguishes between the exposed and unexposed silver halide crystals. It initiates a chemical reaction that reduces the exposed silver halide crystals into metallic silver and creates dark or black areas on a dental radiograph , at the same time unexposed silver halide remains unaffected. Softens the film emulsion during the process. If the film is allowed to stay for longer time in developer, it will slowly initiate reduction of unexposed silver halide results in production of a chemical fog.

39. 2. Rinsing : Film is rinsed in water for 30 seconds with continuous and gentle agitations. Actions: D ilutes the developer present in the emulsion , slowing the developing process . R emoves the alkali activator , preventing neutralization of the acid fixer . Rinsing is not present in automatic processing . 3 . Fixing : Next the film is placed in fixer solution . Actions: Removes the unexposed silver halide crystals and create white or clear areas on the dental radiograph. H elps in hardening and shrinkage of film emulsion.

40. 4. Washing : Following fixing process the film is washed in running water. Actions: To remove any remaining traces of chemical solutions from the emulsion. Precaution : Washing efficiency declines rapidly when water temperature falls below 60 degree F . Warm water should not be used as the emulsion will soften and film will be easily damaged. Any silver compound or thiosulfate that remains because of improper rinsing discolors and causes stains , because of reaction of thiosulfate with the silver to form brown silver sulphide . ( seen as yellow stains/ white deposits)

41. 5 . Drying : After through rinsing the film is dried in drying cabinet hang up in a well ventilated dust free room which is followed by mounting of the radiograph . Precaution : Wet emulsion should not be touched Films should not be splashed with water during the drying cycle as this will produce spots which cannot be removed and reduce the diagnostic value if the film. 6. Mounting of radiograph : More convenient for visualization For record purpose, should be correctly inscribed by patients name, and the relevant date. The convex side of the film corner should be placed towards the viewer.

42. Time temperature method: B est for mass processing of radiographs. Before processing check the levels of developer and fixer solution Replenish solutions, if the solution level is low. Never add water to raise the level of the solution, as it dilutes the strength of the chemicals. Stir the solutions with a stirring rod/paddle. (mixes the chemicals and regularizes the temperature) Check the temperature of developing solution. The optimum temperature is 65 to 75 degree F. If the temperature of the developer solution is outside this range , circulating water tap must be regularized to adjust the temperature. Close and lock the dark room turn off the overhead white light and turn on the safelight. Based on the temperature of developer solution and instruction of manufacture, set the timer.

43. Modified time temperature method : In the method , depending upon the temperature of solution, the developing time is divided on daily basis. A table or a chart can be prepared by specifying developing time for a range of daytime temperature. Advantage: Temperature need not be maintained at particular level and at the same time consistent image quality can be gained.

44. Visual method This manual method consists of placing the film in developing solution and viewing them from time to time in the safe light, thus the degree of developing is at the operators discretion. Advantage : Film can be developed to the contrast and details desired for the particular subject . Disadvantage :Each film has to be processed individually hence very time consuming & is highly objective. Rapid processing chemicals In recent years manufactures have produced rapid processing solutions that typically develop a film in 15 seconds and fix them in 15 seconds at room temperature. They contain higher concentration of hydroquinone and more alkaline pH, which causes the emulsion to swell more, thus providing greater access to the developer. The resultant images do not have the same degree of contrast and discolor over a period of time if not fully washed . However, after viewing ,if these films are kept in the conventional fixing solution for 4 minutes and washed for 10 minutes , the contrast is improved and the film becomes more stable for storage .

45. Automatic method This method uses equipment that automates all the processing steps. They are 2 types Automatic Dunking models that produce a washed film that still has to be dried. 2. Miniature Roller type that produces a dried film.

46. Automatic processor Components of Automatic processor The processor housing encases all the component parts of automatic processor. 2. Film feed slot – is an opening on the outside of the processor housing used to insert unwrapped film into automatic processor. 3. Roller film transporter - consists of series of rollers driven by constant speed motor that operates through gears , belts or chains. These assembles are designed and positioned so that the film crosses over from one roller to next. Function of Rollers : Primarily move the film through the developing solutions, There motion keeps the solution agitated . In the developer , fixer and water tanks , the rollers press on the film emulsion , forcing solution out of the emulsion . The emulsion rapidly fills again with the solution thus promoting solution exchange. The top rollers at the cross over point between the developer and fixer tanks remove rapidly developing solutions, minimizing carry over of the developer into fixer tank.

47. 4) Developer compartment : Holds the developer solution 5) Fixer compartment : Holds the fixer solution - The film is directly transported from the developer solution into the fixer without rinsing step. - The developer and fixer solution in automatic processor are specially formulated , high concentrated chemical solution designed to react at temperatures between 80 and 95degree F – resulting in rapid development. 6) Water compartment : Holds circulating water 7) Drying chambers : - Wet films are transported from water compartment to drying chamber which holds heated air that dry the wet film. 8)Replenisher pump and solution : Used to maintain proper solution concentration and levels automatically. 9) Film recovery slot : Is an opening on the outside of the processing housing where the dry, processed radiograph emerges from automatic processor.

48. ADVANTAGES: - Less processing time is required (less than 4 – 7 minutes) Constant film quality is achieved, due to fixed processing cycles. Less floor space is required Chemicals can be replenished automatically by machine. Large number of films can be processed continuously. DISADVANTAGES : - Quality is not as high as that of manually developed radiograph. – High cost of equipment and maintenance Strict maintenance and regula r change is required, dirty rollers produce marked films.

49. Difference between automatic and manual processing solution No stop bath between developer and fixer as rollers remove the chemicals. Higher temperatures for automatic processors. Therefore different chemicals required with higher concentration. Hardener placed in developer in automatic processors. Additional hardener is added to the fixer solution. Because of the heater in the automatic processor, the process is a ‘dry to dry “ process.

50. Mono bath method : In this method developer and fixer are combined in one solution. The fixer is alkaline and does not neutralize the developer. This monobath is injected into special water proof film packet and the film is developed by simply rubbing the film packet . Disadvantage : Alkaline type of fixer very rapidly oxidizes under atmospheric conditions Results are not satisfactory as the fixing starts while the developing process is in progress.

51. Day light processing method: Any processing method that doesn’t need a dark room is called as daylight processing method. Both manual and automatic processing can be executed in this manner. Manual processing is carried out in a special device provided with safe light filters and two glove like compartments through which the operator can put his hands and develop the films . If an automatic processor has a daylight-loading chamber and since the entire assembly is enclosed in a light proof contains, it also can be called as daylight processing method. Elimination of need for a darkroom is the only advantage in this method.

52. Self Developing Films These are recent advances in manual processing The x –ray film is presented in a special sachet containing developer and fixer. F ollowing exposure the developer tab is pulled , releasing developer solution which is milked down towards the film , and massaged around it . A fter about 30 seconds the fixer tab is pulled to release the fixer solution which is similarly milked down to the film. A fter fixing the used chemicals are discarded , film is rinsed thoroughly under running water for about 10 minutes.

53. A dvantage : No dark room or processing facilities required . Time saving , the final radiograph is ready in about a minute . Disadv antage: P oor over all image quality. R apid destruction of image with time . There is no lead foil inside the film packet . Film packet is very flexible and easily bent. These films are difficult to use in positioning holders.

54. Summary : Film processing refers to a series of steps that produce a visible permanent image on a dental radiograph The pattern of stored energy on an exposed film is termed as a latent image, this image remains invisible until it undergoes processing. The visible image that result on a dental radiograph is made up of black, white, & gray areas. There are 5 steps of film processing: Development, Rinsing, fixation, Washing, Drying A darkroom is a completely dark room where X-ray films can be handled and processed to produce diagnostic radiographs. The ideal darkroom can be conveniently located, adequate size, equipped with correct lighting and ventilation, and arranged with ample working space & storage. The dark must be light tight and must include proper safe light. Manual processing and automatic processing are the practical processing methods for film processing.