Title: Concepts of Panoramic Radiography Theory of Panoramic Imaging
1Concepts of Panoramic RadiographyTheory of
Panoramic Imaging
- DHY 202 Clinical Radiology I
- Dental Hygiene Department
- William Rainey Harper College
2Panoramic Imaging General Principles
- Employs scanography (slit beam) tomography
3Panoramic 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
4Panoramic Imaging General Principles
- Tomography
- used extensively in medicine
- basis for CT (computed tomography) MRI
(magnetic resonance imaging)
5Panoramic 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
6Panoramic 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
7Panoramic 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
8Panoramic Imaging General Principles
Curved surface
- A panoramic radiograph or pantomogram is
produced using curved-surface tomography.
Flat surface
9Panoramic 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
10Panoramic Imaging General Principles
- Client remains stationary as xray tube and film
cassette-holder (which are connected) both rotate
around the client
11Panoramic Imaging General Principles
- A vertical, narrow beam is used compared with the
larger, circular or rectangular beam used in
conventional intraoral radiography
12Panoramic 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
13Panoramic 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)
14Panoramic 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
15Panoramic ImagingProjection in the Horizontal
Plane
- True intraoral source focus of
projection
Effective focus of projection
Rotating beam projected on stationary film
Uniform magnification
16Panoramic 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
17Panoramic 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
18Panoramic 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
19Panoramic Imaging Principles of Image Layer
Formation
- The image layer is called the focal trough
20Panoramic 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
21Panoramic Imaging Principles of Image Layer
Formation
- Objects outside this sharply depicted plane will
appear distorted, fuzzy, or may not be visible
22Panoramic 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)
23Panoramic 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)
24Panoramic 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
25Panoramic Imaging Movement Pattern of the Xray
Beam
- Continuously moving rotation center are most
popular
26Panoramic 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
27Panoramic 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