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Radiographic cassettes


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Radiographic cassettes

  1. 1. Presented by: Sudil Paudyal B.Sc.MIT 1st yr. Roll no.514-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 1
  2. 2. Introduction A radiographic film cassette is a rectangle or square plastic or metallic container used to hold x-ray films (exposed or unexposed) and intensifying screens in close and uniform contact with one another.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 2
  3. 3. Functions1. Hold intensifying screens and protect them from damage.2. Exclude all light from entering the cassette and fogging the film.3. Maintain a close and uniform contact between the film and screens.4. Exclude dust and dirt from the sensitive screens.5. Act as a medium from exposure upto further processing of film.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 3
  4. 4. Features of an ideal cassette1. Lightweight to facilitate easy handling and carrying.2. Easy to open and close under low light conditions.3. No sharp edges or corners which might injure patients or staff.4. Strong and rigid to withstand physical damage from daily wear and tear.5. The front part must provide minimum beam attenuation, be of uniform thickness and have no irregularities.6. Internal rear surface must have an adequate layer of lead foil attached to minimize the risk of back scatter.7. Cassette construction should be so that there is uniform contact between film and screen by the use of foam sponges.8. Availability in range of film sizes. 4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 4
  5. 5. Construction Consists of a front and a back hinged at one edge. Thin sheet of lead foil attached on the back side which is further attached to a plastic foam pressure pad and an i.s. The front, also referred to as cassette wall contains front i.s. and a short lead blocker used for patient identification.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 5
  7. 7. Contd… A range of locking methods are used,from spring clips to sliding locking bars,which serve to exclude light and along with foam pads maintain close contact between film and screens. All the internal metal or plastic surfaces are given black coating to prevent internal light reflections. To ensure good film-screen contact a slightly curved cassette back is used which minimizes photographic unsharpness.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 7
  8. 8. Materials used in cassetteconstruction Nowadays, for lightweight cassette design synthetic materials are used.Cassette front: In order to minimize beam attenuation ,cassette front should confirm to british standards (BS 4304/1968). It states that if metal it should have an Al equivalent of not more than 1.6 mm when used at 60 kvp or if plastic no more than 0.2 mm Al equivalent.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 8
  9. 9.  Metal(e.g. aluminium),plastic laminate or carbon fibre are materials commonly used because of the following advantages: Strength Light weight Low beam absorption The use of carbon fibre cassettes can mean significant reduction in patient dose because of their lower beam attenuation,esp. at low kv.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 9
  10. 10. Cassette back: May be of metal or plastic construction and lined with lead foil to protect from back scattered radiotion from bucky tray or other surface. BS recommendation states that it should have a lead eq. of at least 0.12 mm when used with 150 kv equipment.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 10
  11. 11. Cassette fittings: Clips or fasteners- usually stainless steel Hinges - metal or plastic Presssure pad - plastic foam sponge4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 11
  12. 12. Types of cassettes available1. i) Single screen cassettes: Have a single i.s. Designed to be used with single sided emulsion film Principal application in mammography. ii) Double screen cassettes: Have screen on both sides Used with double sided emulsion film Used in general radiography4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 12
  13. 13. 2. Curved cassettes: Internally constructed as conventional cassette with double sided i.s. Only shape is curved to provide good contact between object and cassette.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 13
  14. 14.  Mainly available in two types:i. First type used when object- cassette contact cannot be achieved with conventional flat cassettesii. Second type used to obtain views of mandible and maxilla in orthodontic radiography4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 14
  15. 15. Fig: Two types of curved cassettes.(a) is used where the necessary close contact between object and cassette cannot be achieved with a conventional cassette.e.g. intercondylar views of flexed knee.(b) is used to obtain panoramic views of mandible (orthopantomography).4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 15
  16. 16. 3. Gridded cassette: Have a secondary radiation grid between the front i.s. and the front of cassette. Used for radiography where a conventional bucky system is unavailable e.g. in ward radiography.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 16
  17. 17. 4. Multi section cassettes: Designed to hold 3-7 films, with their respective i.s. and spacers of about 5 or 10 mm in thicknessAdvantage of using spacers: Films which are separated by 5mm spacers will produce images of body sections 5mm apart and like wise with 10 mm spacers4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 17
  18. 18. Fig. A multisection cassette for tomography. A selection of multisection cassettes are available with a choice of spacers thickness and number of screen pairs.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 18
  19. 19. Uses of multisection cassettes: Most common use in tomography where they are used to produce a set of films each bearing an image of different layer height within the body with one exposure Another use in multiple radiography where by using single exposure different images having varying densities and contrast can be produced4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 19
  20. 20.  In the multiple radiography procedure, the cassette is loaded with a set of films and varying speed i.s. but no spacers. Due to variation in i.s. speeds used, one exposure gives a set of films each with different density range and contrast.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 20
  21. 21. Vacuum cassettes Made from flexible vinyl material Have a valve attached at one end Inside is removable plastic folder containing single i.s. For use a single sided emulsion film is inserted inside the folder . The entire folder is placed inside the cassette and sealed. Vacuum pump is attached to the valve and air expelled, thus bringing the is and film in close contact4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 21
  22. 22. Fig. A vacuum cassette. Once the film has been inserted and the sliding clamp replaced, all air is drawn out via the non return valve thus bringing the film and screen in close contact with one another.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 22
  23. 23. Uses of vaccum cassette: Primarily developed for use in mammography In joint radiography, their inherent flexibility can be used as an advantage in positioning, e.g. under a flexed joint4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 23
  24. 24. Formatter cassettes Consist of frame designed to hold two single sided emulsion films by their edges Also consist of two removable slides which protect the film from light exposure when not in use Do not contain intensifying screensUSES: Used for imaging from CRT and TV monitors in ultrasound, nuclear medicine, CT,DSA and MRI Used in conjunction with formatter or video imager4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 24
  25. 25.  Loaded under safelight conditions by removing the two slides and sliding the individual films, emulsion side facing outward, ensuring that they are securely held in side channels by their long edges Finally the slides are inserted When required for use the cassette is inserted into the multiformat imager and slide nearest to the film to be exposed is removed4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 25
  26. 26. Angiography cassettes Can hold upto 30 sheets of films, size 35*35 cm each positioned with metal spacers After loading and sliding the two panels, the cassette can be inserted into the AOT equipment Exposed films will have been transferred via exposure area of AOT apparatus to the take-up cassette A button on the front is pressed closing the sliding lid The take-up cassette can then be taken to darkroom and processed4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 26
  28. 28. Photo fluorography cassette Photo fluorography or the recording of images from output phosphor of an image intensifier tube is usually carried out on 70 mm or 105 mm roll film or on 100 mm sheet film. All the above various film formats have their individual cassette system.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 28
  29. 29. Computed radiography (CR)cassettes Use PSP plates in place of film and screens The plates are coated with europium- activated Barium Fluoro-Halide (BaFX: Eu 2+). Halide used may be bromide, iodide or a combination of both. Cassettes are used just like conventional cassettes on normal radiographic equipment and available in similar sizes. Information is stored in PSP imaging plates as electrons, in semi-stable higher energy states4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 29
  30. 30. Contd…  Image information is acquired by scanning the plate by a laser beam  Red laser light excites these trapped electrons during scanning  Electrons eject from the higher energy levels and come down to the base level. They emit a higher energy blue light during this process.  This light is captured by a light guide, converted into electrical signals, amplified, digitised and used to form the image.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 30
  31. 31.  The imaging plate is ready for re-use after exposure to white light. Patient information and cassette ID needs to be linked in a CR system , as there is no direct electrical connection between the CR reader and the cassette. A bar code reader or a chip embedded on the CR cassette is used for this purpose.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 31
  32. 32. Figure 2. Schematic of a CR imaging system, screen, and scanner. Samei E et al. Radiographics 2004;24:313-334©2004 by Radiological Society of North America 4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 32
  33. 33. Loading and unloading a cassette: The life of i.s. depends on the care during film loading and unloading. Unloading: Under safelight, the cassette is placed face downwards on the bench and locking clip released. The cassette is then turned over and the front of the cassette is tripped so that the film falls from the cassette well. The film is removed with free hand and the cassette loaded.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 33
  34. 34.  Loading: Under safelights, the cassette is placed face downward on the bench and as before opened from the back. The unexposed film, tightly gripped at its edge is lowered gently into the cassette well. The cassette is closed by bringing over the back and engaging the locking clip.4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 34
  35. 35. Care of cassettes1. Should be treated gently2. Number of cassettes carried at a time should be limited. Should be carried securely between body and arm, with fingers holding their bottom edge.3. If stored on edge, it should be ensured that they are as near vertical as possible4. Contact with fluids should be avoided4-4-2011 RADIOGRAPHIC CASSETTES BY SUDIL 35