Radiology L07 - Projection Geometry

PROJECTION GEOMETRY

INTRAORAL RADIOGRAPHIC TECHNIQUESNotes are under View > Show Speaker Notes- Joel

COPYRIGHTED MATERIAL

Some material in this presentation is copyrighted. This material is only for use by students in this course and is not to be further distributed.

GEOMETRIC CHARACTERISTICS

1. Image unsharpness2. Image magnification3. Image shape distortion

UNSHARPNESS

Fuzzy, unsharp margin of radiographic image.

Penumbra or edge gradient

Miles DA et al. Radiographic imaging for Dental Auxiliaries. Copyright 1989, Saunders.

Rule #1.Radiation source should be as small as possible.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

Rule #2.Source-to-object distance should be as long as possible.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

Intraoral Radiography with Rinn XCP/BAI Instruments. Copyright 1989, Rinn Corp.

Rule #3.Object-to-film distance should be as short as possible.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

Razmus TF, Williamson GF. Current Oral and Maxillofacial Imaging. Copyright 1996, Saunders.

MAGNIFICATION (Equal Enlargement)

Enlargement of radiographic image, compared to actual size of object.

Image shows true shape of object

Rule #1.Source-to-object distance should be as long as possible.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

Rule #2.Object-to-film distance should be as short as possible.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

DISTORTION (Unequal Enlargement)

Variation from true shape of object.Unequal magnification of parts of object.Improper alignment of film, object, beam.

Rule #1:Object and film should be parallel.

Razmus TF, Williamson GF. Current Oral and Maxillofacial Imaging. Copyright 1996, Saunders.

Rule #2:Beam should be perpendicular to object and film.

Razmus TF, Williamson GF. Current Oral and Maxillofacial Imaging. Copyright 1996, Saunders.

Foreshortening

Goaz PW, White SC. Oral Radiology: Principles and Interpretation, 2nd ed. Copyright 1987, Mosby

Elongation

Goaz PW, White SC. Oral Radiology: Principles and Interpretation, 2nd ed. Copyright 1987, Mosby

5 RULES FOR ACCURATE IMAGE FORMATION

1. Focal spot as small as possible.2. Source-object distance as long as possible.3. Object-film distance as short as possible.4. Object parallel to film.5. Beam perpendicular to object and film.

Frommer HH. Radiology for Dental Auxiliaries, 4th ed.Copyright 1987, Mosby.

DIAGNOSTIC QUALITY OF RADIOGRAPHS

1. Proper visual characteristics2. Minimal geometric characteristics3. Anatomic accuracy of image4. Film coverage of anatomic region

ANATOMIC ACCURACY

1. Labial and lingual CEJ of anteriors superimposed2. Buccal and lingual cusps of posteriors superimposed3. Contacts of teeth opened.4. Buccal and lingual aspect of alveolar crest superimposed.5. No superimposition of zygoma over roots

Langland OE, Langlais RP, Preece JW. Principles of Dental Imaging, 2nd ed. Copyright 2002, Williams & Wilkins.

FILM COVERAGE

1. Area of interest shown2. Periapical coverage (2-4 mm)3. Supplemental views

INTRAORAL RADIOGRAPHIC TECHNIQUES

PROJECTION TECHNIQUES FOR PERIAPICAL RADIOGRAPHY

1. Paralleling Technique – use long cone2. Bisecting Angle Technique – use long or short cone

PARALLELING TECHNIQUE

1. Film parallel to tooth

increased object-film distanceincreased source-film distance

2. Beam perpendicular to tooth/film.

Razmus TF, Williamson GF. Current Oral and Maxillofacial Imaging.Copyright 1996, Saunders.

VERTICAL ANGULATION

Intraoral Radiography with Rinn XCP/BAI Instruments. Copyright 1989, Rinn Corp.

HORIZONTAL ANGULATION

Intraoral Radiography with Rinn XCP/BAI Instruments. Copyright 1989, Rinn Corp.

ALIGNMENT OF BEAM AND FILM

Miles DA et al. Radiographic imaging for Dental Auxiliaries.Copyright 1989, Saunders.

Intraoral Radiography with Rinn XCP/BAI Instruments. Copyright 1989, Rinn Corp.

●Paralleling technique is the preferred method.

●If the paralleling technique cannot be used, the bisecting angle technique may be used.

Razmus TF, Williamson GF. Current Oral and Maxillofacial Imaging.Copyright 1996, Saunders.

BISECTING ANGLE TECHNIQUE

Based on Rule of Isometry:

If two triangles have two equal angles and a common side, then the two triangles are equal.

Miles DA, Van Dis ML, Razmus TF. Basic Principles of Oral and Maxillofacial Radiology. Copyright 1992, Saunders.

BISECTING ANGLE TECHNIQUE

The angle formed by plane of tooth and plane of film is bisected, and the beam is directed perpendicular to the bisecting line.

White SC., Pharoah MJ. Oral Radiology: Principles and Interpretation, 6th ed. Copyright 2009, Mosby

FORESHORTENING

Tooth not parallel to film, and beam directed perpendicular to film.

ELONGATION

Tooth not parallel to film, and beam directed perpendicular to tooth.

Improper horizontal angulation results in overlapping of contacts.

Miles DA et al. Radiographic imaging for Dental Auxiliaries.Copyright 1989, Saunders.

Improper alignment of beam and film results in cone cutting.

Miles DA et al. Radiographic imaging for Dental Auxiliaries.Copyright 1989, Saunders.

BITEWING TECHNIQUE

Crowns, interproximal areas and alveolar bone support

Caries, periodontal condition, calculus, crown margins

Premolar and molar bitewing

Intraoral Radiography with Rinn XCP/BAI Instruments. Copyright 1989, Rinn Corp.

BITEWING TECHNIQUE

Miles DA, Van Dis ML, Razmus TF. Basic Principles of Oral and Maxillofacial Radiology. Copyright 1992, Saunders.

RADIOGRAPHIC LOCALIZATION

1. Right angle method2. Buccal object rule

SLOB – same lingual, opposite buccal.

Right Angle Method

Buccal Object Rule

Goaz PW, White SC. Oral Radiology: Principles and Interpretation, 2nd ed. Copyright 1987, Mosby

Buccal Object Rule

Goaz PW, White SC. Oral Radiology: Principles and Interpretation, 2nd ed. Copyright 1987, Mosby

Buccal Object Rule

Buccal Object Rule

Richards AG. Buccal object rule. Dent Radiogr Photogr 1980; 53:37.Copyright, Eastman Kodak.