1. Concepts of Panoramic Radiography Theory 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 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

15. 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

16. Panoramic Imaging: Projection 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