Projection Geometry: Intraoral Radiographic technique (Exam 2) Flashcards
Geometric characteristics include: (3)
- Image sharpness
- Image magnification
- Image shape distortion
Fuzzy, unsharp margin of radiographic image:
Unsharpness
Penumbra:
The unsharp margin of the image
Umbra:
Shadow
We want to minimize the _____ or maximize the ____
unsharpness; sharpness
What are the three rules to maximize sharpness?
- Radiation source should be as small as possible
- Source-to-object distance should be as long as possible
- Object-to-receptor distance should be as short as possible
What is the benefit of having a smaller focal spot?
Fewer X-ray photons that interact with the edge of the object leading to a sharper image
When we say the Source-to-object distance should be as long as possible, what is the source?
The focal spot
The closer the object is to the focal spot, the more _____ the X-ray photons are that are going to interact with the edges of the tooth
Divergent
The shorter the source-to-object distance, the greater the ______ meaning _____
Penumbra; the greater the unsharpness of the margin
How do we control the source-to-object distance?
By the length of the cone (longer cones better)
(its not exactly synonymous to source-to-object distance but we think of it as this way)
The X-rays beams will be more parallel to the object if we use a:
Longer cone
We have greater _____ with a longer object-to-receptor distance
Penumbra
You want the object or tooth to be as close to the ____ as possible
Image receptor
The equal enlargement of the object:
Magnification
Two rules to minimize magnification:
- source-to-object distance should be as long as possible
- object-to-receptor distance should be as short as possible
Enlargement of radiographic image, compared to actual size of object:
Magnification
If the distance from the source to the tooth is short then the X-rays that interact with the tooth are still going to be fairly _____ leading to ____
Divergent; greater magnification
If the distance form the source to the tooth is longer than the X-ray beam that interacts with the tooth is going to be fairly ____ leading to ____
Parallel; less magnification
Shape distortion has more to do with ____ than ____
Angles; distance
Unequal enlargement:
Distortion
not only is the object larger but the shape is inaccurate:
Distortion
Variation from true shape of object; unequal magnification of parts of object:
Distortion
Distortion can be caued by:
Improper alignment of receptor, object or beam
What are the rules for minimizing distortion?
- object and receptor should be parallel
- beam should be perpendicular to object & receptor
CR in the diagrams stands for:
Central ray
The radiographic image of the object is shorter than///
Foreshortening
Tooth is not parallel to receptor and beam directed perpendicular can lead to what type of distortion?
Forshortening & elongation
The radiographic image is longer than the object itself:
Elongation
Tooth not parallel to receptor, and beam directed perpendicular to tooth:
Elongation
Five rules for 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
Projection techniques for periapical radiography: (2)
- paralleling technique - use long cone
- bisecting angle technique - use long or short cone
What are the two steps to the paralleling technique?
- receptor parallel to tooth
- beam perpendicular to tooth/receptor
In the paralleling technique when having the receptor parallel to the tooth, we want _____ object-receptor distance, and ____ source-receptor distance
increased; increased
What balances out the increased object-receptor distance when using the paralleling technique?
increased source-to-receptor distance (minimizing unsharpness & magnification)
What type of cone is used to increase the source-to-receptor distance using the paralleling technique?
Long cone
Getting the image receptor parallel to the teeth allows for correct _____ angulation
vertical
If you’re using the XCP correctly and you line up the beam with the cone, the X-ray beam will image:
the entire area of interest (no cone cuts)
Getting a cone cut autonatically means you have to retake image (T/F):
False (as long as you obtain the area of interest you don’t have to retake)
Cone cuts show up on radiographs as:
White areas
If the contacts are open in the area of interest this tells us the _____ angulation is correct
horizontal
The _____ is the preferred technique but the ___ technique may be used if the first choice technique does not work
Paralleling technique; bisecting angle technique
With the bisecting angle technique, you are not trying to get the image receptor parallel to the tooth, but rather just trying to get it _____ to the tooth
Close
The bisecting angle technique is based on:
The rule of isometry
In the bisecting angle technique, if two triangles have two equal angles and a common side, then:
The two triangles are equal
According to the bisecting angle technique if you direct the X-ray being perpendicular to the bisecting line that you estimated when lining things up you should:
Get a pretty good image
The bisecting angle technique states that the angle formed by the plane of the tooth and plane of receptor is bisected and the beam is directed ____ to the bisecting line
Perpendicular
Why is the paralleling technique preferred over the bisecting angle technique?
a little more distortion with the bisecting angle technique
preferred image for checking bone level:
Bitewing
The ___ technique has more limitations than the ____ technique
Bisecting angle technique; paralleling technique
The bitewing is used to see:
Crowns, interproximal bone levels, alveolar bone support, caries, periodontal condition, calculus and crown margins
Bitewings are not used to view:
Periapical regions of the tooth
Bitewing technique : The ____ angle is more of a challenge than the ___ angle
Horizontal; vertical
In the bitewing technique, you’d like us to have a _____ vertical angulation
slightly positive (+5 to 10 degrees depending on location)
If the horizontal angulation is incorrect in bitewing radiographs, then the image will display:
Overlapping contacts
____ includes periapical and bitewing radiographs showing all teeth
Full mouth series
When viewing radiographs, whats on the providers right is actually the patients:
Left
Radiographic localization includes: (2)
- right angle method
- tube shift method (SLOB)
States if you take radiographs at right angles to eachother of the areas of interest you can localize the area in question:
Right angle method
The right angle method states:
if you take radiographs at right angles to eachother of the areas of interest you can localize the area in question:
SLOB stands for:
Same Lingual Opposite Buccal
In the tube shift method, you will take a second radiograph of the same area but alter the:
Horizontal angulation
In the tube shift method, if you take the first radiograph straight on, you may take the second radiograph _____ (for example)
mesially or distally (or even vertically)
If the object moves in the same diredction as you move the tube head, than the object is ____ to the reference point (same)
Lingual
When using the slob rule, if the object moves in the opposite direction as the tube head was moved, than the object is ____ to the reference point (opposite)
Buccal
First radiograph: supernumerary tooth overlapping mesial of the root
Using SLOB method you move tube mesially in second radiograph
Second radiograph: the supernumerary tooth now does not overlap the mesial root of the second molar (shifter slightly mesial)
This means the lesion is:
Lingual
The tube shift method for radiographic localization may also be referred to as:
SLOB
Edge gradient; the unsharp area; area around the margins of the object:
Penumbra
What do we try to minimize when taking radiographs?
Penumbra
How do we minimize penumbra?
By having an increased source to object ratio
Three factors that affect the quality of a ra
