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Extraoral RadiologyOctober 10th, 2008

Steven R. Singer, DDSsrs2@columbia.edu212.305.5674

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

1

Thank you!