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Concepts of Panoramic Radiography Theory of Panoramic Imaging. DHY 202 Clinical Radiology I Dental Hygiene Department William Rainey Harper College. Panoramic Imaging : General Principles. Employs scanography (slit beam) & tomography. Panoramic Imaging : General Principles.

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concepts of panoramic radiography theory of panoramic imaging

Concepts of Panoramic RadiographyTheory of Panoramic Imaging

DHY 202 Clinical Radiology I

Dental Hygiene Department

William Rainey Harper College

panoramic imaging general principles
Panoramic Imaging : General Principles
  • Employs scanography (slit beam) & tomography
panoramic imaging general principles3
Panoramic Imaging : General Principles
  • Tomography: allows radiographing in one plane of an object while blurring or eliminating images from structures in other planes.
  • “Tomo” is Greek for section
  • View sections or radiographic slices
panoramic imaging general principles4
Panoramic Imaging : General Principles
  • Tomography
    • used extensively in medicine
    • basis for CT (computed tomography) & MRI (magnetic resonance imaging)
panoramic imaging general principles5
Panoramic Imaging : General Principles
  • Tomogram
    • Client remains stationary while xray source & film move in opposite directions in a fixed relationship through one or a series of rotation points. Rotation points can be inside or outside of the focal trough
panoramic imaging general principles6
Panoramic Imaging : General Principles
  • Focal trough in tomogram
    • Or “plane of acceptable detail,” or “image layer,” is the plane that is not blurred on the radiograph
panoramic imaging general principles7
Panoramic Imaging : General Principles
  • Focal trough in pantogram
    • Width & thickness governed by many factors
    • Objects lying within the focal spot are shown clearly; objects outside are blurred
panoramic imaging general principles8
Panoramic Imaging : General Principles
  • A panoramic radiograph or pantomogram is produced using curved-surface tomography.

Curved surface

Flat surface

panoramic imaging general principles9
Panoramic Imaging : General Principles
  • Rotational panoramic radiography is accomplished by rotating a narrow beam of radiation in the horizontal plane around an invisible pivot point/axis positioned intraorally.
  • Film & tube travel in opposite directions around the client
panoramic imaging general principles10
Panoramic Imaging : General Principles
  • Client remains stationary as xray tube and film cassette-holder (which are connected) both rotate around the client
panoramic imaging general principles11
Panoramic Imaging : General Principles
  • A vertical, narrow beam is used compared with the larger, circular or rectangular beam used in conventional intraoral radiography
panoramic imaging general principles12
Panoramic Imaging : General Principles
  • The pivot point/axis is called therotation center
  • The center of rotation changes as the film and tubehead rotate which allows the image layer to conform to the elliptical shape of the dental arches
panoramic imaging projection in the vertical plane
Panoramic Imaging: Projection in the Vertical Plane
  • Vertical dimension unaffected by horizontal rotation
  • Vertical angulation same as conventional intraoral projection
  • Slight negative angulation; passes beneath occipital area (-4 to -7 degrees)
panoramic imaging projection in the horizontal plane
Panoramic Imaging:Projection in the Horizontal Plane
  • Horizontal image affected by horizontal rotation of the beam
  • Xrays appear to diverge from intraoral source but really originate outside of the client
  • Apparent intraoral source is called the center of rotation
panoramic imaging projection in the horizontal plane15
Panoramic Imaging:Projection in the Horizontal Plane

True intraoral source & focus of projection

Effective focus of projection

Rotating beam

projected on

stationary film

Uniform magnification

panoramic imaging projection in the horizontal plane16
Panoramic Imaging:Projection in the Horizontal Plane

Rotating beam and

moving film has

proportions restored

  • Discrepancy in horizontal versus vertical magnification eliminated by using a moving film to equalize the magnification in the horizontal dimension with the vertical
  • Film moves in direction opposite to the horizontal rotation of the beam
panoramic imaging principles of image layer formation
Panoramic Imaging: Principles of Image Layer Formation
  • Film placed on circular drum or a moving flat cassette
  • Horizontal magnification is reduced to match vertical magnification by adjusting speed of film in respect to projection of beam
panoramic imaging principles of image layer formation18
Panoramic Imaging: Principles of Image Layer Formation
  • Vertical and horizontal dimensions match only when the object lies within a particular plane called the central plane or sharply depicted plane of the image layer
panoramic imaging principles of image layer formation19
Panoramic Imaging: Principles of Image Layer Formation
  • The image layer is called the focal trough
panoramic imaging image layer focal trough defined
Panoramic Imaging: Image Layer/Focal Trough Defined
  • A three-dimensional zone in which structures are reasonably well-defined
  • A zone in an object defined as containing those object points depicted with sufficient detail to be distinguished
  • Determines where dental arches must be positioned to achieve clearest image
panoramic imaging principles of image layer formation21
Panoramic Imaging: Principles of Image Layer Formation
  • Objects outside this sharply depicted plane will appear distorted, fuzzy, or may not be visible
panoramic imaging width of the image layer
Panoramic Imaging: Width of the Image Layer
  • Determined by
    • Distance from center of rotation to central plane of image layer
    • Width of long, narrow slit beam (the narrower the beam , the wider the image layer)
panoramic imaging position of the image layer
Panoramic Imaging: Position of the Image Layer
  • Changes in film speed alter the position of the image layer
    • Increased film speed = image farther away from rotation center
    • Decreased film speed = image closer to rotation center
  • This is how the image layer is shaped to center the jaws (anteriors narrower)
panoramic imaging movement pattern of the xray beam
Panoramic Imaging: Movement Pattern of the Xray Beam
  • Movement pattern of the xray beam chosen to obtain a favorable projection of the jaws
  • Depending on the manufacturer, number and location of rotational centers differ
panoramic imaging movement pattern of the xray beam25
Panoramic Imaging: Movement Pattern of the Xray Beam
  • Continuously moving rotation center are most popular
panoramic imaging image layer analysis
Panoramic Imaging: Image Layer Analysis
  • Objects closest to film will be narrowed
  • Objects closest or toward the source will be widened
  • Buccal objects projected lower
  • Lingual objects projected higher
  • Objects in the center of the layer are magnified 20-30%
panoramic imaging image layer analysis27
Panoramic Imaging: Image Layer Analysis
  • Less definition than than intraoral film
  • More horizontal than vertical magnification
  • All objects, even those outside the focal trough are projected onto the film, but most are not seen
  • Objects with the greatest density are displayed in two places: intended image and ghost image