Presentation is loading. Please wait.

Presentation is loading. Please wait.

Concepts of Panoramic Radiography Theory of Panoramic Imaging DHY 202 Clinical Radiology I Dental Hygiene Department William Rainey Harper College.

Similar presentations


Presentation on theme: "Concepts of Panoramic Radiography Theory of Panoramic Imaging DHY 202 Clinical Radiology I Dental Hygiene Department William Rainey Harper College."— Presentation transcript:

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) & tomographyEmploys 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.Tomography: allows radiographing in one plane of an object while blurring or eliminating images from structures in other planes. “Tomo” is Greek for section“Tomo” is Greek for section View sections or radiographic slicesView sections or radiographic slices

4 Panoramic Imaging : General Principles TomographyTomography –used extensively in medicine –basis for CT (computed tomography) & MRI (magnetic resonance imaging)

5 Panoramic Imaging : General Principles TomogramTomogram –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 tomogramFocal 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 pantogramFocal 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 A panoramic radiograph or pantomogram is produced using curved-surface tomography.A panoramic radiograph or pantomogram is produced using curved-surface tomography. Curved surface 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.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 clientFilm & 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 clientClient 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 radiographyA 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 centerThe 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 archesThe 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 rotationVertical dimension unaffected by horizontal rotation Vertical angulation same as conventional intraoral projectionVertical angulation same as conventional intraoral projection Slight negative angulation; passes beneath occipital area (-4 to -7 degrees)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 beamHorizontal image affected by horizontal rotation of the beam Xrays appear to diverge from intraoral source but really originate outside of the clientXrays appear to diverge from intraoral source but really originate outside of the client Apparent intraoral source is called the center of rotationApparent 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 Uniform magnification Rotating beam projected on stationary film

16 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 verticalDiscrepancy 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 beamFilm moves in direction opposite to the horizontal rotation of the beam

17 Panoramic Imaging: Principles of Image Layer Formation Film placed on circular drum or a moving flat cassetteFilm 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 beamHorizontal 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 layerVertical 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 troughThe 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-definedA 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 distinguishedA 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 imageDetermines 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 visibleObjects outside this sharply depicted plane will appear distorted, fuzzy, or may not be visible

22 Panoramic Imaging: Width of the Image Layer Determined byDetermined by Distance from center of rotation to central plane of image layerDistance 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)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 layerChanges in film speed alter the position of the image layer Increased film speed = image farther away from rotation centerIncreased film speed = image farther away from rotation center Decreased film speed = image closer to rotation centerDecreased film speed = image closer to rotation center This is how the image layer is shaped to center the jaws (anteriors narrower)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 jawsMovement pattern of the xray beam chosen to obtain a favorable projection of the jaws Depending on the manufacturer, number and location of rotational centers differDepending 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 popularContinuously moving rotation center are most popular

26 Panoramic Imaging: Image Layer Analysis Objects closest to film will be narrowedObjects closest to film will be narrowed Objects closest or toward the source will be widenedObjects closest or toward the source will be widened Buccal objects projected lowerBuccal objects projected lower Lingual objects projected higherLingual objects projected higher Objects in the center of the layer are magnified 20-30%Objects in the center of the layer are magnified 20-30%

27 Panoramic Imaging: Image Layer Analysis Less definition than than intraoral filmLess definition than than intraoral film More horizontal than vertical magnificationMore horizontal than vertical magnification All objects, even those outside the focal trough are projected onto the film, but most are not seenAll 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 imageObjects with the greatest density are displayed in two places: intended image and ghost image


Download ppt "Concepts of Panoramic Radiography Theory of Panoramic Imaging DHY 202 Clinical Radiology I Dental Hygiene Department William Rainey Harper College."

Similar presentations


Ads by Google