1. Chapter 6 Image Receptors Radiology

2. Introduction To further understand radiography, one must know how a permanent record is produced using x-rays. To further understand radiography, one must know how a permanent record is produced using x-rays. Radiograph is formed with light- sensitive film contained in a light- proof encasement. Radiograph is formed with light- sensitive film contained in a light- proof encasement. Encasement in radiography is called a cassette. Encasement in radiography is called a cassette.

3. The Cassette Designed to hold a piece of x-ray film sandwiched between two fluorescent sheets of plastic called INTENSIFYING SCREENS. Designed to hold a piece of x-ray film sandwiched between two fluorescent sheets of plastic called INTENSIFYING SCREENS. Intensifying screens are responsible for converting the x-ray radiation into visible light, which creates a latent image on the x-ray film.Intensifying screens are responsible for converting the x-ray radiation into visible light, which creates a latent image on the x-ray film. Film is then processed to convert latent image to visible image.Film is then processed to convert latent image to visible image. Only 5 % of exposure results from ionization of x-rays, rest is due to light emitted from intensifying screens.Only 5 % of exposure results from ionization of x-rays, rest is due to light emitted from intensifying screens.

4. The Cassette Cassette- A rigid film holder designed to hold x-ray film and intensifying screens in close contact. Cassette- A rigid film holder designed to hold x-ray film and intensifying screens in close contact. Constructed with light tight materials to prevent unwanted exposure, but yet still allow penetration of x-rays. Constructed with light tight materials to prevent unwanted exposure, but yet still allow penetration of x-rays. Originally cassettes were made with cardboard, but could not be reused. Originally cassettes were made with cardboard, but could not be reused. Different forms today include aluminum, polycarbonate, magnesium, and carbon fiber. Different forms today include aluminum, polycarbonate, magnesium, and carbon fiber.

5. The Cassette Attached to the back with hinges and catches. Attached to the back with hinges and catches. Forms light tight seal.Forms light tight seal. Back of cassette is constructed with heavier material than the front because is lined with material to absorb backscatter. Back of cassette is constructed with heavier material than the front because is lined with material to absorb backscatter. Sides are lined with felt or foam pressure pads that ensure close contact of the film to the intensifying screens. Sides are lined with felt or foam pressure pads that ensure close contact of the film to the intensifying screens.

6. The Cassette Sizes vary. Sizes vary. Correspond to screen and film sizes.Correspond to screen and film sizes. Cost varies as well. Cost varies as well.

8. Cassette Care Should always be handled with care. Should always be handled with care. Can be exposed to large amounts of physical abuse. Can be exposed to large amounts of physical abuse. Common damage includes:Common damage includes: Dropping the cassette. Dropping the cassette. Leakage of fluid on the cassette. Leakage of fluid on the cassette. May want to place in plastic bag when a “messy” situation occurs.

9. Cassette Care continued Should be cleaned on regular basis with mild soap and water. Should be cleaned on regular basis with mild soap and water. Should clean exterior and interior of cassettes at least once monthly. Should clean exterior and interior of cassettes at least once monthly. Cassettes should be numbered so that problems can be easily identified. Cassettes should be numbered so that problems can be easily identified. Intensifying screens are already numbered, but can add number onto intensifying screen.Intensifying screens are already numbered, but can add number onto intensifying screen.

10. The Cassette Color coding is sometimes used to identify type of screen inside. Color coding is sometimes used to identify type of screen inside. Front of cassette may be divided into four quadrants. Front of cassette may be divided into four quadrants. Shield other quadrants so that multiple views can be taken per film.Shield other quadrants so that multiple views can be taken per film. Lead blocker (approximately 3x7 cm) is found in corner of cassette. Lead blocker (approximately 3x7 cm) is found in corner of cassette.

11. Lead Blocker

12. Present to prevent irradiation of the part of the film necessary for identification. Present to prevent irradiation of the part of the film necessary for identification. Careful not to have image in area of lead blocker. Careful not to have image in area of lead blocker.

13. Intensifying Screens Intensifying screens- sheets of luminescent phosphor crystals bound together and mounted on a cardboard or plastic base. Intensifying screens- sheets of luminescent phosphor crystals bound together and mounted on a cardboard or plastic base. Two screens are normally in an x-ray cassette and sandwich the film. Two screens are normally in an x-ray cassette and sandwich the film. Film has a coating of light sensitive emulsion on both sides (Double emulsion).Film has a coating of light sensitive emulsion on both sides (Double emulsion).

14. Intensifying Screens When phosphor crystals in screen are hit by x-radiation, the crystals fluoresce, and x-rays are converted to visible light. When phosphor crystals in screen are hit by x-radiation, the crystals fluoresce, and x-rays are converted to visible light. Visible light is what exposes the film. Visible light is what exposes the film. Primary purpose of screen is to reduce the amount of radiation exposure required to produce a diagnostic radiograph. Primary purpose of screen is to reduce the amount of radiation exposure required to produce a diagnostic radiograph.

15. Intensifying Screens Reduces the amount of mAs needed, which in turn decreases the dose of radiation to the patient and the chance of motion on the radiograph. Reduces the amount of mAs needed, which in turn decreases the dose of radiation to the patient and the chance of motion on the radiograph. Three properties determine efficiency of screen materials. Three properties determine efficiency of screen materials. 1. They must have a high level of x-ray absorption.1. They must have a high level of x-ray absorption. 2. They must have high x-ray to light conversion with suitable energy and color.2. They must have high x-ray to light conversion with suitable energy and color. 3. There must be little or no “afterglow” once radiation has ceased.3. There must be little or no “afterglow” once radiation has ceased.

16. Screen Construction Has four layers Has four layers A base or supportA base or support A reflective layerA reflective layer A phosphor crystal layerA phosphor crystal layer A protective coatA protective coat

17. Base Serves as flexible support to attach the phosphor layer to the cassette. Serves as flexible support to attach the phosphor layer to the cassette. Base must have tough, moisture- resistant surface and not become brittle with extended use. Base must have tough, moisture- resistant surface and not become brittle with extended use.

18. The Reflective Layer Attached to the base. Attached to the base. Made of a white substance such as titanium dioxide. Made of a white substance such as titanium dioxide. Purpose is to reflect light emitted by phosphor layer back toward the x- ray film. Purpose is to reflect light emitted by phosphor layer back toward the x- ray film. Increases the efficiency of the screen so that no light is lost through the base. Increases the efficiency of the screen so that no light is lost through the base.

19. Phosphor Crystal Layer Consists of uniformly distributed phosphor crystals held in place with binder material. Consists of uniformly distributed phosphor crystals held in place with binder material. Layer can not change in thickness, crack or discolor with age as any variance will alter amount of light produced and alter exposure of film. Layer can not change in thickness, crack or discolor with age as any variance will alter amount of light produced and alter exposure of film.

20. Phosphor types Phosphor chosen must absorb x-rays efficiently and have minimum afterglow and emit sufficient light of the desired color. Phosphor chosen must absorb x-rays efficiently and have minimum afterglow and emit sufficient light of the desired color. Afterglow- tendency of phosphor to still give off light after x-radiation has stopped. Afterglow- tendency of phosphor to still give off light after x-radiation has stopped. Absorption rate of phosphor refers to the extraction of x-ray photons from the beam. The more x-ray quanta absorbed, the greater the amount of light produced. Absorption rate of phosphor refers to the extraction of x-ray photons from the beam. The more x-ray quanta absorbed, the greater the amount of light produced.

21. Protective Coat Is a clear coating placed on the outer surface of the screen. Is a clear coating placed on the outer surface of the screen. Provides protection to the phosphor layer. Provides protection to the phosphor layer. Must be strong enough to resist marks and abrasions and must be easy to clean. Must be strong enough to resist marks and abrasions and must be easy to clean.

22. Screen Speed General Rules: General Rules: Large crystal: Faster screens-less detail- high grain.Large crystal: Faster screens-less detail- high grain. Small crystals: Slower screens-more detail- low grain.Small crystals: Slower screens-more detail- low grain.

23. Screen Speeds Calcium tungstate- high x-ray absorption ability and physically strong but lacks in light conversion ability. Calcium tungstate- high x-ray absorption ability and physically strong but lacks in light conversion ability. Rare-earth elements- higher x-ray to light conversion ability. Rare-earth elements- higher x-ray to light conversion ability. Other factors can affect screen speed aside from phosphor type. Other factors can affect screen speed aside from phosphor type. Governed by crystal size, phosphor layer thickness, reflective layer efficiency, and dyes in the phosphor layer.Governed by crystal size, phosphor layer thickness, reflective layer efficiency, and dyes in the phosphor layer.

24. Crystal Size Larger the crystal, greater the light emission. Larger the crystal, greater the light emission. X-ray strikes crystal, entire crystal starts to fluoresce. X-ray strikes crystal, entire crystal starts to fluoresce. Thus need less x-radiation. Thus need less x-radiation. However detail of image decreases as crystal size increases.However detail of image decreases as crystal size increases.

25. Phosphor Layer Thickness When thickness is increased, x-ray absorption and light emission are increased. When thickness is increased, x-ray absorption and light emission are increased. Increase in thickness results in decrease of image detail. Increase in thickness results in decrease of image detail.

26. Reflective Layer Efficiency Is positioned between base and phosphor layer. Is positioned between base and phosphor layer. Purpose is to reflect all light emission from phosphor layer toward x-ray film. Purpose is to reflect all light emission from phosphor layer toward x-ray film. Needs to be high in reflective ability in order to decrease x-radiation needed. Needs to be high in reflective ability in order to decrease x-radiation needed.

27. Dyes in the Phosphor Layer Light absorbing dye may be incorporated into the binder material of the phosphor layer in some screens. Light absorbing dye may be incorporated into the binder material of the phosphor layer in some screens. Dye is to decrease lateral spreading of the light emitted from the phosphor crystals. Dye is to decrease lateral spreading of the light emitted from the phosphor crystals. May reduce light emitted and speed of screen. May reduce light emitted and speed of screen.

28. Screen Speed Ratings Many screens to choose from. Many screens to choose from. Screens divided into three categories: Screens divided into three categories: SlowSlow MediumMedium FastFast

29. Slow Screens Also called high definition, ultra- detail, or fine grain. Also called high definition, ultra- detail, or fine grain. Specifically designed from radiographic examinations that require optimal detail and in which exposure time is not critical. Specifically designed from radiographic examinations that require optimal detail and in which exposure time is not critical.

30. Medium Screens Also referred to as Regular, midspeed, normal or par speed. Also referred to as Regular, midspeed, normal or par speed. Most common in private veterinary practice. Most common in private veterinary practice. Provide good resolution with low exposures. Provide good resolution with low exposures.

31. Fast Screens Also referred to as High Speed. Also referred to as High Speed. Reduces exposure time to patient. Reduces exposure time to patient. Able to penetrate thick tissue where more exposure is necessary. Able to penetrate thick tissue where more exposure is necessary. Less detail. Less detail.

32. Screen Speeds May depend on manufacturer May depend on manufacturer Quantum Mottle- an artifact of faster screens that results in density variations due to random spatial distribution of the phosphor crystals within the screen. Quantum Mottle- an artifact of faster screens that results in density variations due to random spatial distribution of the phosphor crystals within the screen. Gives radiographs a spotted or mottled appearance.Gives radiographs a spotted or mottled appearance.

33. Intensifying Screens Continued Usually mounted in pairs in the cassette. Usually mounted in pairs in the cassette. Labeled front and back and should be placed accordingly. Labeled front and back and should be placed accordingly. Should be firmly mounted in cassette. Should be firmly mounted in cassette.

34. Screen Care Should be inspected and cleaned on regular basis. Should be inspected and cleaned on regular basis. Try to keep free from dust and animal hair. Try to keep free from dust and animal hair. After cleaning, should be left open to completely dry before reloading. After cleaning, should be left open to completely dry before reloading.

37. X-ray Film Purpose is to provide a permanent record containing essential diagnostic information Purpose is to provide a permanent record containing essential diagnostic information Consists of polyester base coated on both sides with light-sensitive emulsion containing silver halide crystals. Consists of polyester base coated on both sides with light-sensitive emulsion containing silver halide crystals. When visible light or x-rays interact with silver halide crystals, latent image is formed. Through processing, this is converted to a visible image. When visible light or x-rays interact with silver halide crystals, latent image is formed. Through processing, this is converted to a visible image.

38. Film Composition Layers include: Layers include: Base- flexible support with adhesive coating on each side.Base- flexible support with adhesive coating on each side. Emulsion- next to base. Composed of gelatin containing silver halide crystals.Emulsion- next to base. Composed of gelatin containing silver halide crystals. Supercoat- protective material to decrease the possibility of damage to emulsion.Supercoat- protective material to decrease the possibility of damage to emulsion.

39. Latent image An invisible image on the x-ray film after it is exposed to ionizing radiation or visible light before processing. An invisible image on the x-ray film after it is exposed to ionizing radiation or visible light before processing. After processing is converted to a visible image. After processing is converted to a visible image. Silver hallide crystals converted to metallic silver that are exposed. Silver hallide crystals converted to metallic silver that are exposed. If not exposed, will be clear. If not exposed, will be clear.

40. Film Types Screen Film Screen Film Manufactured with silver crystals that are sensitive to fluorescent light emitted from intensifying screens and less sensitive to ionizing radiation.Manufactured with silver crystals that are sensitive to fluorescent light emitted from intensifying screens and less sensitive to ionizing radiation. Requires less exposure to x-rays to produce quality image.Requires less exposure to x-rays to produce quality image.

41. Film Type Continued Nonscreen Film Nonscreen Film Exposed by the direct action of x- radiation.Exposed by the direct action of x- radiation. More sensitive to ionizing radiation.More sensitive to ionizing radiation. Requires greater exposure because there is no intensifying screens.Requires greater exposure because there is no intensifying screens. No real protective layer.No real protective layer.

42. Film Speed Speeds are determined from exposures required to produce an image with adequate density. Speeds are determined from exposures required to produce an image with adequate density. Film latitude- The exposure range of a film that will produce acceptable densities.Film latitude- The exposure range of a film that will produce acceptable densities.

43. Film Speed Types Fast Film (Ultraspeed) Fast Film (Ultraspeed) Larger silver halide crystalsLarger silver halide crystals Requires less exposure to x-rays or fluorescent light from intensifying screens.Requires less exposure to x-rays or fluorescent light from intensifying screens. Produces grainier image that lacks definition.Produces grainier image that lacks definition. Less latitude in exposure factors and processing.Less latitude in exposure factors and processing.

44. Film Speeds Medium Film (Standard or Pat speed) Medium Film (Standard or Pat speed) Most widely used.Most widely used. Compromises between fine grain and speed.Compromises between fine grain and speed. Has medium latitude.Has medium latitude. Suitable for a wide range of examinations.Suitable for a wide range of examinations. Standard by which manufacturers rate other films.Standard by which manufacturers rate other films.

45. Film Speeds Slow Film Slow Film Smaller halide crystalsSmaller halide crystals Requires greater exposure by x-rays or fluorescent light from intensifying screens.Requires greater exposure by x-rays or fluorescent light from intensifying screens. Less grainy and more defined image.Less grainy and more defined image. Greater latitude.Greater latitude.

46. Film Care Film boxes should be stored on end so film is vertical. Film boxes should be stored on end so film is vertical. If stored horizontally too long, emulsions will blend together between the films.If stored horizontally too long, emulsions will blend together between the films. Temp should be cool with low humidity. Temp should be cool with low humidity. Should not be stored close to ionizing radiation, or where vapors can reach it. Should not be stored close to ionizing radiation, or where vapors can reach it. Should be checked regularly for expiration. Should be checked regularly for expiration.