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Concepts of Panoramic Radiography Theory of Panoramic Imaging

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Theory of Panoramic Imaging. DHY 202 Clinical Radiology I. Dental ... Imaging : General ... Client remains stationary while xray source & film move in ... – PowerPoint PPT presentation

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Title: Concepts of Panoramic Radiography Theory of Panoramic Imaging


1
Concepts of Panoramic RadiographyTheory of
Panoramic Imaging
  • DHY 202 Clinical Radiology I
  • Dental Hygiene Department
  • William Rainey Harper College

2
Panoramic Imaging General Principles
  • Employs scanography (slit beam) tomography

3
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

4
Panoramic Imaging General Principles
  • Tomography
  • used extensively in medicine
  • basis for CT (computed tomography) MRI
    (magnetic resonance imaging)

5
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

6
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

7
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

8
Panoramic Imaging General Principles
Curved surface
  • A panoramic radiograph or pantomogram is
    produced using curved-surface tomography.

Flat surface
9
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

10
Panoramic Imaging General Principles
  • Client remains stationary as xray tube and film
    cassette-holder (which are connected) both rotate
    around the client

11
Panoramic Imaging General Principles
  • A vertical, narrow beam is used compared with the
    larger, circular or rectangular beam used in
    conventional intraoral radiography

12
Panoramic Imaging General Principles
  • The pivot point/axis is called the rotation
    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

13
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)

14
Panoramic ImagingProjection 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

15
Panoramic ImagingProjection in the Horizontal
Plane
  • True intraoral source focus of
    projection

Effective focus of projection
Rotating beam projected on stationary film
Uniform magnification
16
Panoramic ImagingProjection in the Horizontal
Plane
  • 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
  • Rotating beam and
  • moving film has
  • proportions restored

17
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

18
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

19
Panoramic Imaging Principles of Image Layer
Formation
  • The image layer is called the focal trough

20
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

21
Panoramic Imaging Principles of Image Layer
Formation
  • Objects outside this sharply depicted plane will
    appear distorted, fuzzy, or may not be visible

22
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)

23
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)

24
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

25
Panoramic Imaging Movement Pattern of the Xray
Beam
  • Continuously moving rotation center are most
    popular

26
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

27
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
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