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Extra-oral Radiology Techniques I

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Radiology
Third Year

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Extra-oral Radiology Techniques I

  1. 1. EXTRA ORAL Radiographic TECHNIQUES PART I By Dr. Hassan M. Abouelkheir BDS, MSC, PHD.
  2. 2. Extra oral Radiography: • All extra oral radiographic projections should be performed using screen film. • Medium or high speed (rare-earth) screenfilm combination are recommended to reduce pt’s exposure. • Metallic letters (L) &(R) are used to determine left & right sides of pt as well as grids to reduce the fog.
  3. 3. Rigid metal cassette Flexible vinyl cassette
  4. 4. Intensifying Screen Function  One of the properties of x-rays is that they cause certain materials to fluoresce (emit light); the phosphor crystals found in intensifying screens are one of these materials. The light emission is usually green or blue, depending on the type of phosphor crystal used.
  5. 5. Intensifying Screen Function  The composition of the films used with these screens is adjusted by the manufacturer to be sensitive to either blue light or green light.  correct film should be used with corresponding screen type. (Bluesensitive film with blue lightemitting screen, etc.)
  6. 6. Screen Film • Screen film is sensitive to the effects of light from an intensifying screen. When these screens, on either side of the film in a cassette, are exposed to x-rays, they emit light which in turn exposes the film. • Using the screen-film combination allows a very large reduction in the amount of radiation needed to expose the film (30-60 times less radiation than that required by direct exposure film).
  7. 7. Intensifying Screen Composition (this side toward film) The base of the screen (yellow line above) is made of above plastic and provides support. A reflecting layer (silver line) reflects light emitted by the phosphor line back toward the film. The phosphor layer (green line) line contains the phosphor crystals that emit the light. The surface of the phosphor layer is covered with a protecting coat (white line) , which is a thin layer of plastic that protects the phosphor layer from damage when the screens are handled.
  8. 8. Rare Earth Phosphor The most common type of phosphors being used are the rare earth phosphors, which emit blue or green light depending on the type of rare earth material being used. film = phosphor crystal
  9. 9. Intensifying Screen Speed The speed of the screen depends on crystal size and the thickness of the phosphor layer (larger crystals and thicker layer increase speed). Image quality decreases as the screen speed increases. The three speeds are: • Fast (Rapid): requires the least exposure but the images are less sharp • Medium (Par): medium speed, medium sharpness • Detail (Slow): produces the sharpest images but requires the most exposure
  10. 10. Screen Film The two types of screen film used with rare earth screens are T-Mat and Ektavision. These films are available in three styles: G, which is used to provide the best contrast; L, which has the widest latitude (long-scale contrast) and is good for soft tissue visualization and H, which is used to provide an extra film for referral purposes (two films are placed in the cassette at the same time). The advantage of Ektavision film over T-Mat film is that it has anti-crossover layers incorporated into the film. This prevents light from one screen affecting both emulsion layers; this produces a sharper image on the film.
  11. 11. T-Mat (crossover) Light produced by the phosphor crystal spreads out as it goes toward the film and with T-Mat film it affects the emulsion on both sides. Since it has spread out more when it reaches the emulsion on the opposite side of the film (crossover), the crossover sharpness (edge detail) of the image is decreased. film
  12. 12. Ektavision (anti-crossover) Ektavision film has a crossover control layer on each side of the film base. These layers allow the light from a phosphor crystal to reach the emulsion on the same side as the crystal but prevent the light from reaching the emulsion on the opposite side of the film. X-rays easily pass through this anticrossover layer. film
  13. 13. Types of Extra-Oral Radiographic Examination: • 1- Mandibular oblique lateral (Ramus, Body). • 2- True Lateral (Cephalometric). • 3-Submento-Vertex view. • 4- Water’s projection (Occipito-Mental). • 5- Postero-Anterior projection. • 6- Reverse Town’s projection.
  14. 14. 1] Lateral oblique projection: • 2 views for mandibular projection; • a) body projection: • For demonstration premolar-molar region and inferior border of the body of the mandible. • Head position: Head tilted to the side to be examined with the mandible protruded.
  15. 15. Lateral oblique projection body (cont.): • Film placement: • Film is placed against the patient’s cheek and centered over the first molar . • The lower border of the cassette should be parallel to the inferior border of the mandible and at least 2cm below it. • Point of entry: • 2cm below angle of the mandible directed toward the 1st molar region of cassette side.
  16. 16. Lateral oblique projection body (cont.):
  17. 17. B) Mandibular Ramus projection: • To view the ramus from the mandibular angle to the condyle for examining the 3rd molar region of both the maxilla and mandible. • Head position: head tilted towards the projected mandible where the mandibular angle of tube side and condyle of cassette side parallel to the floor.
  18. 18. Mandibular ramus projection (cont.): • Film placement : • film is placed over the ramus of the mandible to the far posterior to include the condyle. Lower border of the cassette 2cm below the inferior border of the mandible. • Point of entry: • 2cm below the inferior border of the first molar region on the tube side toward the center of the ramus of the cassette side.
  19. 19. Mandibular ramus projection (cont.):
  20. 20. 2- True Lateral (Cephalometric): Cephalo=Head • Metric=Measurement. Cephalometrics introduced for use by orthodontists by Dr. Broadbent in 1931 for studying dento -facial growth.
  21. 21. True Lateral (Cephalometric) (cont.): • Uses: • • • • • • Evaluation of facial growth & development. Le Fort I & II fractures. Posterior wall of antera. Perforation of hard palate. A foreign body in the air way. The film: is positioned parallel to the sagittal plane of the film. • The central ray :is ┴ the film in both horizontal & vertical plane.
  22. 22. True Lateral (Cephalometric) (cont.): • Reproducibility: • Cephalometric has the unique property of presenting a reproducible image, unlike any other radiographic technique used for dental films
  23. 23. True Lateral (Cephalometric) (cont.): • Reproducibility: • The patients head is oriented in the same position relative to the xray beam every time a film is taken, with the use of positioning ear posts
  24. 24. True Lateral (Cephalometric) (cont.): The distance from the x-ray source to the patient’s midsagittal plane is always the same 60 inches to reduce the magnification.
  25. 25. • Soft tissue profile can be added by using reducing the exposure to 50% or put aluminum filter in the front of cassette.
  26. 26. Uses in orthodontics: • Evaluate skeletal patterns (bone-to-bone relations) • Does the patient have a Class I, Class II or Class III skeletal pattern? • Is the problem due to a prognathic maxilla, a retrognathic maxilla, a prognathic mandible, a retrognathic mandible or a combination of these?
  27. 27. Cephalometric Landmarks • Landmarks are locations which represent biological homology between image locations • Example: The tip of the chin in one cephalometric image corresponds to the tip of the chin in another cephalometric image
  28. 28. Cephalometric Landmarks • Landmarks need to have 3 properties: 1.Landmarks should not remodel over time (neither be created nor destroyed) 2.Landmarks need to capture biological form, including the shape, size and position of the tissue component of which it represents 3.Landmarks have to be reliably located on cephalometric radiographs
  29. 29. Common landmarks • Sella Turcica (S): • midpoint of the pituitary fossa. • Orbitale (O): lowest point on lower margin of orbit
  30. 30. Orthodontic tracing • To the fixed anatomical points is applied to assess the nature and extent of any malocclusion which may be present. • Tracing of anatomical landmarks should be drown with sharp , hard (6H) pencil on good quality tracing paper or acetate drafting sheet not on the film and done on film viewer.
  31. 31. Main areas of concern: - Skeletal relationships. - Dento-skeletal relationships. - The facial profile. Radiographs can be digitized and measured in personal computer with special software or cephalometric tracer attached to computer can be used.
  32. 32. 4-Submentovertex (SMV) view: • The projection shows the base of the skull, Sphenoidal sinuses and facial skeleton from below(radiographic baseline is vertical). • The pt’s head tipped backwards and x-ray beam is aimed upwards at 5° to the horizontal.
  33. 33. Submentovertex Identify location of condyles Image zygomatic arch fracture MSP FP extraoral x-ray unit floor floor
  34. 34. 4-Submentovertex (SMV) view: • Film placement: cassette ± floor and placed vertically. • Head position: tipped backward & touch the cassette .Frankfort plane ± floor. • Beam alignment: • center to the head and ± cassette.
  35. 35. 4-Submentovertex (SMV) view:
  36. 36. Zygomatic Arch View Reduce exposure to 1/3 SV setting
  37. 37. Indications: 1- Destructive lesions affecting the palate, pterygoid region or base of the skull. 2- Investigations of sphenoidal sinuses.
  38. 38. Indications(cont.) : 3- Assessment of the thickness of the posterior part of the mandible before osteotomy. 4- Fracture of the zygomatic arches.
  39. 39. The End

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