Extra Oral
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Transcript of Extra Oral
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Extraoral RadiologyOctober 10th, 2008
Steven R. Singer, [email protected]
November 8th, 1895
Extraoral Projections
Images can be produced in thedental office
X-ray source can be
Intraoral X-ray machine
Combination Pan/Ceph
Medical
Dedicated Cephalometric machine
Film-Screen Combinations
Used for extraoral radiographs to reduce bothpatient dose and time of exposure.
Image quality is slightly reduced over directfilm, such as intraoral projections
Based on the ability of X-ray photons to causefluorescence
Screen film is sensitive to both x-ray photonsand blue or green light. Dyes are included infilm emulsions, making the emulsion sensitiveto light emitted by the screens at a specificwavelength/color.
Film-Screen Combinations
FluorescenceCertain materials fluoresce, that is, theyabsorb radiation and immediately emit light.
The intensity of the light emitted depends onthe intensity of the incident radiation. Thephotographic effect on the film, is the sum ofthe effects of the x-rays and of the lightemitted by the screens. Light emission stopsimmediately when the exciting radiation stops.Fluorescence, as used in radiology, is thus theability of phosphors to emit light when excitedby x-rays.
Film-Screen Combinations
Most of the image is produced by thevisible light photons
Faster screens reduce dose at theexpense of image quality
Size and shape of phosphor crystals inscreens affect image quality
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Film-Screen Combinations
Screens and film must be matched
Screens are used in pairs, as film isdouble-sided
Three types of screens:
1. Standard blue light-emitting calciumtungstate
2. Rare Earth green light-emittinggadolinium or lanthanum
3. Combination
Rare Earth Screens
Rare-earth compounds in these screensconvert x-ray energy into image-creating light more efficiently thanconventional blue-light-emittingscreens, reducing radiation exposure topatients by as much as 50 percent.
Screen Selection and Application
GuideSpeed Classification:
System Basics
1/81/41/21x 2Exposurealteration
compared to
class 100
12.5mAs25mAs50mAs100mAs200mAsRequired mAs
change to
producesimilar
densities
(fixed kV + ffd)
80040020010050Speedclass
Digital Image Receptors
Storage Phosphors CCD/CMOS
Size of Image Receptors
Cephalometric and Skull views:
20x25 cm (8x10 inches)
Lateral Oblique views13x18 cm (5x7 inches)
Panoramic views
12.7x30.5 cm (5x12 inches)
-or-
15x30 cm (6x12 inches)
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Common Extraoral Views
From: White and Pharoah 5th edition
Projection of the Central Ray
The central ray is directed perpendicular to the
plane of the film in the horizontal and verticaldimensions from a source 91 to 102 cm (36 to40 inches) away. The source should becoincident with the midsagittal plane of thehead at the level of the bridge of the nose.
For cephalometric applications the distanceshould be 152.4 cm (60 inches) between thex-ray source and the midcoronal plane. Thisincreased distance provides an resultantimage with a broader gray scale. of thepatient.
Reference Planes Reference Planes
a b
c
d
e
a=canthomeatal plane c=coronal plane e=axial plane
b=Frankfort Horizontal plane d=sagittal plane
Posteroanterior View
Indications:
Disease
Trauma Developmental
abnormalities
Growth anddevelopment
PA Ceph Projection
The image receptor is placed infront of the patient,perpendicular to the midsagittalplane and parallel to thecoronal plane
The patient is placed so thatthe canthomeatal line forms a10-degree angle with thehorizontal plane and theFrankfurt plane is perpendicularto the image receptor. In thePA skull projection, the C-M lineis perpendicular to the imagereceptor.
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PA Ceph Projection PA Projection
PA
LandmarksLateral Skull View
Indications
Trauma
Disease
Developmentalabnormalities
Lateral Cephalometric Projection
The image receptor is positionedparallel to the patient'smidsagittal plane. The side ofinterest is placed toward theimage receptor to minimizedistortion.
In cephalometric radiography,the patient is placed with theleft side toward the imagereceptor, and a wedge filter atthe tube head is positioned overthe anterior aspect of the beamto absorb some of the radiationand allow visualization of softtissues of the face.
Lateral Cephalometric Projection
Unevenmagnification of leftand right sides
Structures close tothe midsagittal plane(e.g., the clinoidprocesses andinferior turbinates)should be nearlysuperimposed.
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Lateral Skull Landmarks Lateral Cephalometric Projection
Submentovertex View
Indications
View base of skull,position ofcondyles,sphenoid sinuses
Fractures of thezygomatic arch(Jughandle View)
Submentovertex Projection
AKA Base projection
Submento-
vertex
Projection
Check to see thesymmetry
Buccal and lingualcortical plates of themandible projectedas uniform opaquelines
Submento-
vertex
Projection
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Submento-
vertex
Landmarks
Submentovertex Projection
Jug handle view
Submentovertex Jughandle ViewOccipeto-Menton Projection
aka Waters View
Indications
Evaluation of themaxillary sinus
Evaluation of thefrontal sinus
View of orbit andnasal fossa
Occipeto-Menton Projection
AKA Watersprojection
C-M plane forms~37 angle withthe imagereceptor
Occipeto-Menton Projection
Petrous ridge
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Lateral Oblique Views
Largely replaced bypanoramic views
Indications:
Position of impactedthird molars
Fractures of theramus, condyle, orbody of the mandible(but not symphysis)
Lateral Oblique Projection
The image receptor is placed
against the patient's cheek onthe side of interest andcentered in the molar-premolararea. The lower border of thecassette is parallel and at least2 cm below the inferior borderof the mandible. The head istilted towards the side beingexamined, and the mandible isprotruded.
The central ray is directedtoward the premolar-molarregion from a point 2 cm belowthe opposite angle of themandible.
Lateral Oblique Projection Lateral Oblique Projection-Body
Body of the mandible
Alveolus, teeth and the
body of the mandible
between canine and
the third molar region
Lateral Oblique Projection-
Ramus Ramus
Also known asLateral ramus view
Reverse Towne View
Indications:
Suspectedfracture of thecondylar neck
Showsposterolateral wallof maxillary sinus
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Reverse Towne projection
-300
Reverse Towne projection
-300
Townes
LandmarksPanoramic View
Comparative views Linear Tomography
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Trans-cranial views Trans-pharyngeal
Trans-orbitalSelection Criteria
From: White and Pharoah 5th edition
Selection Criteria
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