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Conventional (Body Section) Tomography

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    Conventional (Body Section) Tomography Conventional (Body Section) Tomography Presentation Transcript

      • Plain Film
      • Tomography
      Resident Physics Lectures George David Associate Professor Department of Radiology Medical College of Georgia
    • Body Section Tomography
      • Not CT
      • Body Section Imaging
      • Goal
        • keep plane of interest in focus
        • blur all other plans
          • enhances contrast
      • Popularity decreasing because of
        • CT
        • MRI
    • Tomography History
      • Predates CT by decades
      • Used to be popular for inner ear studies
      • Still used at MCG for IVP’s
    • Tomography Blurring
      • Blurring accomplished by synchronous movement of tube & film
        • tube & bucky physically connected by rod
        • rod pivots around fulcrum
        • tube moves one direction
        • film moves in other direction
    • Conventional Tomography Blurring
      • Image produced on film
      • Objects above or below fulcrum plane change position on film & thus blur
    • Tomography Blurring
      • the further from the fulcrum an object is, the more it blurs!
    • Tomography Blurring
      • objects shaped & oriented in direction of motion
        • elongate
        • do not blur
    • Tomographic Blurring
      • Blurring improved by use of complex motions
        • circular
        • tri-spiral
        • elliptical
      Hypocycloidal
    • Complex Blurring
      • The more complex the blurring motion
        • the sharper the tomographic image
          • better blurring
        • the more expensive the machine
      $
    • Tomo Patient Doses
      • Tomo can be high dose procedure
        • several rads not unusual
      • one image per cut with film
        • cuts at many levels routinely employed to find cut of interest
        • each cut exposes entire field
      • Can do multiple images per cut with digital receptor
    • Thickness of Cut
      • Same as thickness of region in focus
      • Determined by angle tube moves
      • Larger angles yield thinner cuts
        • more motion = more blurring
      • Smaller angles yield thicker cuts
        • 0 o (stationary) yields conventional film
    • Thickness of Cut Smaller Angle; Thicker Cut Larger Angle; Thinner Cut
    • Cut Thickness
      • Approximate cut thickness for linear tomo
      Tomo Angle Thickness of Cut (mm) (degrees) ------------------------------------------------------- 0 Infinite (non-tomo) 2 31 4 16 6 11 10 6 20 3 35 2 50 1
    • Grids & Tomo
      • Linear grid used
      • Grid lines parallel with table for linear tomo
      • Grid must change orientation (rotate) in complex motion tomo
        • eliminates grid cutoff