KAMBALE MATABISHI - IMAGE FORMATION, LATENT IMAGE AND X-RAY PROCESSING.pptx

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1. IMAGE FORMATION, LATENT IMAGE AND X-RAY FILM PROCESSING PRESENTER : Dr. KAMBALE MATABISHI FACILITATOR : Dr. FAROUK

2. Outlines I ntroduction The formation of an invisible image The conversion of the invisible X-ray image i nto a visible light image Latent image X-ray Film processing S ummary

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

4. To produce a radiographic image, x ray photon must pass through tissue and interact with an image receptor such as imaging plate in computed radiography(CR). As the primary x ray beam interacts with the anatomic part, photons are absorbed, scattered and transmitted. Finally, the radiation that exits the patient is composed of varying energies and interacts with the image receptor to form latent images and which are processed to form radiographic image.

5. Flow of information from the patient to the observer, it is considered in three distinct stages: - Stage I: The formation of an invisible or latent X -ray image - Stage 2: The conversion of the invisible X-ray image into a visible light image - Stage 3: The viewing, perception and interpretation of the visible image

6. Stage I: The formation of an invisible X -ray image When X-ray beam of uniform intensity passes from the X-ray tube into the patient, the beam carries no information about the patient. As the beam penetrates through the body tissues it becomes modified, each part of the beam being attenuated to a degree which depends on the particular tissue it has passed. When the beam emerges from the patient it is no longer uniform, it displays a pattern of intensities which carries information about the structures the beam has penetrated. R efer to this pattern of intensities as the invisible X ray image.

7. Stage 2: The conversion of the invisible X-ray image into a visible light image (1) By employing the photographic effect of X-rays on a sheet of sensitive film. Photographic material used for this purpose is known as direct-exposure X-ray film. (2) By employing the xeroradiographic process. An electrically charged imaging plate is exposed in a similar way to an X-ray film (3) By employing the fluorescent effect of X-rays on a sensitive screen. Fluorescent screen used in this way is known as an intensifying screen, while the film which records its image is referred to as a screen-type X-ray film. (4)By employing the process of photon stimulated luminescence A phosphor-coated imaging plate is exposed in a similar fashion to an X-ray film The light output is detected and converted to a digital signal on a TV monitors known as computed radiography (CR).

8. Stage 3: The viewing, perception and interpretation of the visible image. The diagnostic image, whether it be on photographic film or on a television screen, must be viewed and understood before a diagnosis can be made. The diagnostic information carried by such images can only be communicated effectively to an observer under optimum viewing conditions.

9. What is an image A radiographic image is created by passing an x-ray beam through the patient and interacting with an image receptor. (1) Real images : those having a real, physical existence such as photographic or radiographic images which are accessible to scientific measurement and objective study . ( 2) Mental images : those generated as mental pictures within our own minds and which are accessible only to subjective study

10. As the primary x-ray beam interacts with the anatomic part, photons are absorbed , scattered and transmitted . The differences in the absorption characteristics of the anatomic part create an image that structually represents the anatomic part.

11. Factors affecting beam attenuation The amount of x-ray beam attenuation is affected by: The thickness of the anatomic part, Its atomic number and tissue density , The energy of the x-ray beam

12. 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 chemical altered of crystals are said to constitute the latent (invisible) image of the film. These chimical changes in the cristals increase the liability of crystals to the chimical 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 .

13. L atent image refers to the image that exist on the film after that film has been exposed but before it has been chemically processed. The specific way in which latent image is formed is not well known. But the Gurney- mott theory of latent image formation is most widely beloved to best explain the manner in which the process at molecular level in the emulsion layer of film, specifically what happens to the silver crystal when exposed to x ray and light. Mitchell theory also explain the formation of latent image.

14. Formation of latent image The x-ray photon will strike the phosphor crystal in the screen. The excited phosphor will emit a specific wavelength of light that exposed the film. The light breaks down of the Silver- Iodo -Bromide crystals to release the Silver ions. Metallic silver is black, so it is this metallic silver that produces black areas on a developed film. The more is the quantity of x-ray received, the more the light produced and the more metallic silver ions produced hence the darker the film – shades of greyness. The image formed is the Latent Image.

15. GURNEY-MOTT THEORY of latent image formation Six stages of latent image formation : Stage 1: before exposure to x-ray or light photons Stage 2: exposure to photons Stage 3: trapping of wondering electron Stage 4: attraction for silver ions Stage 5: Deposition of mettalic silver Stage 6: R eoccurence of stages 2-5. The cycle reoccurs and more metallic sliver is deposited a t the sensitivity speck

16. The Dark Room Dark room is the pace where the necessary handling and processing of films can be carried out safely a nd efficiently , w ithout the hazard of producting « film fog  » byb accidental exposure to light or x-rays. The primary function of the dark room is to provide a completely darkned environlment 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 equipement must be in a specific place.

17. Near total darkness means safe illumination. It must exclude all outside light and provide safe artificial light . The temperature and humidity level of the dark room must be controlled to prevent film damage. A room temperature of 70 degrees F (21 degree Celcuis ) 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 tancks .

18. VISIBLE IMAGE FORMATION IN FILM SCREEN RADIOGRAPHY What is visible image? - >A radiographic image that can be seen. Different methods of chemical processing

19. 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

20. 1. Manuel film processing It Consists of 5 steps : development Rinsing Fixing Washing Drying

21. FILM PROCESSING Series of events after the film is exposed to X-rays There is another stage in the manual processing known as rinsing in between development and fixing.

22. a ) Development The film is placed in a developer solution for a specific amount of time at a specific temperature. It amplifies the latent image by a factor of millions to form a visible silver pattern. The developer solution contains a reducing agent which donates electrons to development center(sensitivity speak ). These electrons completely reduce the exposed silver halides grains to metallic silver.

23. Constituents of developing solution 1) Solvent (2 ) Developing agent (3) Accelerator (4) Buffers (5) Restrainers ( 6) Preservative (7) Hardener (8) Sequestering agent

24. Solvent Water is the solvent used in radiographic processing. It acts as the carrying medium in which the developer constituents are dissolved. Tap water is cheap and universally available, contains dissolved mineral salts, calcium salts If present in the high concentrations such minerals may precipitate out of solution, forming a chalky deposit or scum on the surface of films processed in the solutions. Manufacturers anticipate this tendency by including water-softening agents (sequestering agents ).

25. Developing agents Phenidone and hydroquinone Are reducing agents, primary function of supplying the electrons that convert the exposed silver halide grains to silver. Characteristics : They must be selective and distinguish effectively between exposed and unexposed grains They must be of sufficiently high activity to allow complete development of the film in a relatively short time, e.g. 20-30 seconds, They must be as resistant as possible to the presence of bromine ions in solution.

26. Factors affecting development The conversion of the invisible latent image into a visible radiographic image takes place during the developing stage in the processing cycle. The factors which influence the quantity and quality of development are: ( 1) Constitution of developing solution. ( 2) Developer temperature. ( 3) Development time.

27. I ) Constitution of developing solution Choice of developing agents and their relative proportions . This affects what we might term the inherent characteristics of the developer. X-ray film developers are high-energy, high-contrast developers . Concentration of developing agents in solution . In general, higher concentrations result in greater activity but eventually lead to increased chemical fog.

28. 2 ) Developer temperature In general, developer activity increases with temperature, Temperature control is therefore an essential feature of processor design. High-temperature development developer temperatures of up to 42°C were necessary to permit 90 s processing cycle times . Low-temperature development low-temperature developers operate at around 30°C and can still produce very rapid results . Medium-temperature development Most modern developers operate within a midrange of temperatures (e.g. between 33- 37°C ) offering dry-to-dry processing cycle times of 90 to 160 seconds .

29. 3) Development time T ime elapses between the entry of a specified part of a film (e.g. its leading edge) into the developing solution and the exit from the developing solution of the same part of the film. Advantages of short time (I) Patient waiting times in the X-ray minimized ( 2) Examination times can be decreased (3 ) waiting lists reduced.

30. b) Rinsing Film is rinsed in water for 30 seconds with continous and gentle agitations. Actions: Dilutes the developer present in the emulsion , sloing the develping process Removes the alkali activator , preventing neutralization of the acid fixer Rinsing is not present in automatic processing .

31. c) Fixing or fixation Second stage in automatic processing, the film is placed in fixer solution. It has four major functions : To stop any further development ; To clear the image by removing the unexposed silver halide crystals; To fix the image, i.e. to render it chemically stable so that it undergoes no further changes and is no longer photosensitive To complete the process of hardening of the film emulsion.

32. Constituents of fixing solution Fixer replenished consists of : ( 1) Solvent ( 2) Fixing agent ( 3) Acid fixer ( 4) Hardener ( 5) Buffer ( 6) Preservative ( 7) Anti- sludging agent.

33. Constituents of fixing solution 1)Solvent Water is the solvent and diluent used in fixing solution. 2) Fixing agent A fixing agent eg ammonium thiosulphate is a chemical which combines with the largely insoluble silver halide in the film emulsion to form soluble compounds which can diffuse and be washed out of the emulsion . 3 ) Acid Fixer solution eg acetic acid is made acidic To ensure that development ceases when a film enters the fixer. If development is allowed to continue in the fixer staining · of the image may occur. 4) Hardener - emulsion hardening to limit water uptake by the emulsion is essential in automatic processing bcoz It reduces drying time and It prevents physical damage to the emulsion surface.

34. Constituents of fixing solution 5) Buffer eg Sodium acetate Precise control of pH of fixer is important in order to : Prevent sulphurization,Ensure neutralization of developer , Maintain optimum hardener activity . 6 ) Preservative eg sodium sulphite The preservative in fixer retards the decomposition of thiosulphates and thus delays the onset of sulphurization . 7 ) Anti- sludging agen t eg boric acid,The aluminium salts used as hardeners have a tendency to produce insoluble aluminium compounds.

35. Factors that influence quality of fixation 1. Constitution of fixing solution -ammonium thiosulphate which gives a rapid-acting, high-energy fixer. 2. Fixer temperature -The activity of fixing agents increases with temperature and at higher temperatures diffusion processes are more rapid and the emulsion gelatin, though more permeable, is softer and susceptible to damage 3.Fixer time -During the time taken for a film to pass through the fixing solution, the developer in its emulsion must diffuse out, fixing solution must diffuse in and the processes of clearing and hardening must be completed. In a 90 s processing cycle, about 15 s is available for the fixing stage, while in manual processing the fixing time may be as long as 5 min.

36. d ) Washing When a film leaves the fixing tank its emulsion is saturated with fixing solution contaminated with silver complexes and ammonium halides. If such chemicals are not removed, the emulsion will gradually acquire a yellow-brown sulphur stain during storage. Additionally , dissolved salts may crystallize out into the surface of the film. Tap water is the best washing agent for automatic processor. Action: to remove any remaining traces of chemical solutions from emulsion

37. e )Drying The final stage in the processing of a radiograph is to remove all of the surface water and most of that retained in its emulsion . Precaution: Wet emulsion should not be touched Films should not be splashed with water during the drying cycle as this will produce spots which can not be removed and reduce the diagnostic value o f the film.

38. SYSTEMS OF THE AUTOMATIC PROCESSOR The Film Feed Section Transport System Temperature Control System Recirculation System Replenishment System Dryer System Electrical System

39. Daylight Automatic Processors Enable film to be processed without need for darkroom Special cassettes Increase in department efficiency, no need for special darkroom staff Disadvantages Cost Mechanical breakdowns Enable film to be processed without need for darkroom Special cassettes Increase in department efficiency, no need for special darkroom staff Disadvantages Cost Mechanical breakdowns Enable film to be processed without need for darkroom Special cassettes Increase in department efficiency, no need for special darkroom staff Disadvantages Cost Mechanical breakdowns

40. Automatic film processing: benefits Compact size Faster Density and contrast is constant Time and temperature controlled Produces dry radiograph immediately

41. Automatic film processing: disadvantages Artifacts caused by rollers. Expensive and requires maintenance. Manual processing required as a back up in case of break down

42. S ummary Film processing refers to a serie 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 inviisible until it undergoes processing . The visible image that result on a dental radiograph is made up of black, white and gray areas. There are 5 steps of film processing : Developing , Rinsing , fixing, washing and drying .

43. 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 and storage . The dark must be light and must include proper safe light. Manual processing and automatic processing are the pratical processing methods for film processing .

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