PROJECTION GEOMETRY INTRAORAL RADIOGRAPHIC TECHNIQUE Flashcards
What are the different geometric characteristics?
1.Image sharpness
2.Image magnification
3.Image shape distortion
What is unsharpness?
- Fuzzy, unsharp margin of radiographic image.
- Penumbra or edge gradient
What are the 3 rules to maximize sharpness?
Rule #1.
- Radiation source should be as small as possible.
Rule #2.
- Source-to-object distance should be as long as possible.
Rule #3.
- Object-to-receptor distance should be as short as possible.
To maximize sharpness the radiation source should be as ____ as possible
small
What is a pneumbra?
edge gradient
- blurriness
To maximize sharpness the source-to-object distance should be as _____ as possible
long
To maximize sharpness the object-to-receptor distance should be as _____ as possible
short
Can you adjust the size of the radiation source to adjust sharpness?
No, the companies/manufacturers decide this
Why should the object-to-receptor distance be as short as possible?
photons will not diverge as much after they interact with the tooth before getting to the receptor
Why should the source-to-object distance be as long as possible?
photons will be less divergent and more parallel before interacting with tooth
What is magnification (equal enlargement)?
- Enlargement of radiographic image, compared to actual size of object.
- Image shows true shape of object
What are the two rules to minimize magnification?
Rule #1.
- Source-to-object distance should be as long as possible.
Rule #2.
- Object-to-receptor distance should be as short as possible.
To minimize magnification the source-to-object distance should be as _____ as possible
long
To minimize magnification the object-to-receptor distance should be as _____ as possible
short
What is distortion (unequal enlargement)?
- Variation from true shape of object.
- Unequal magnification of parts of object.
- Improper alignment of receptor, object, beam.
What are the two rules to minimize shape distortion?
Rule #1:
- Object and receptor should be parallel.
Rule #2:
- Beam should be perpendicular to object and receptor
To minimize shape distortion the object and receptor should be _______
parallel
To minimize shape distortion the beam should be _________ to object and receptor?
perpendicular
What are the two types of distortion?
- foreshortening
- elongation
What is foreshortening?
Tooth not parallel to receptor, and beam directed perpendicular to the RECEPTOR.
What is elongation?
Tooth not parallel to receptor, and beam directed perpendicular to the TOOTH
What are the 5 rules for an accurate image formation?
- Focal spot as small as possible.
- Source-object distance as long as possible.
- Object-receptor distance as short as possible.
- Object parallel to receptor.
- Beam perpendicular to object and receptor.
What projection technique do we use at UMKC?
paralleling technique
What cone can you use for the paralleling technique?
long cone
What cone can you use for the bisecting angle technique?
long or short cone
What are the two projection technqiues for periapical radiography?
- Paralleling technique
- Bisecting Angle technique
What is the preferred method of projection technqiues for periapical radiography?
paralleling technique
What is the paralleling technique?
1.Receptor parallel to tooth
–increased object-receptor distance
–increased source-object distance
2. Beam perpendicular to tooth/receptor.
What are the two techniques for the paralleling technique?
- vertical angulation
- horizontal angulation
What are you wanting to see on periapical radiographs?
- at least 2 mm of bone surrounding the roots of the teeth
- if contacts can be seen then the horizontal angulation was correct
What is the bisecting angle technique based on?
Rule of isometry
What is the rule of isometry?
If two triangles have two equal angles and a common side, then the two triangles are equal.
What is the bisecting angle technique?
The angle formed by plane of tooth and plane of receptor is bisected, and the beam is directed perpendicular to the bisecting line.
What are you trying to view/diagnose with a bitewing?
- crowns
- interproximal areas
- alveolar bone support
- caries
- periodontal condition
- calculus
- crown margins
What would happen on a bitewing radiograph if you have an incorrect horizontal angulation?
overlapped contacts
What are the two methods for radiographic localization?
- Right angle method
- Tube shift method (SLOB)/Buccal object rule
What method of radiographic localization is shown?
right angle method
What method of radiographic localization is shown?
tube shift method (SLOB)/buccal object rule
Why would you need to use radiographic localization?
- radiographs only show something in 2 planes
- if you need to see exactly where something is located you need more “planes” to visualize it
