Projection Geometry: Intraoral Radiographic Technique- 9/19- DONE over powerpoint but add study guide stuff Flashcards
Geometric characteristics include: (3)
- image sharpness
- image magnification
- image shape distortion
Fuzzy, unsharp margin of radiographic image:
unsharpness
Penumbra:
unsharp margin of the image
umbra:
shadow
We want to minimize ____ or maximize ____
unsharpness; sharpness
What are the 3 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
The source is the ____, when referring to “source-to-object”
focal spot
The closer the object is tot he focal spot, the more___ the x-ray photons are that are going to interact with the edge 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 course-to-object distance?
by the length of the cone
We prefer to use a ___ cone than a ___ cone because the x-rays that interact with the object are more parallel which will maximize sharpness.
longer cone; shorter cone
You want the object or tooth to be as close to the ____ as possible
image receptor
We have greater ____ with longer object-to-receptor distance
Penumbra
The equal enlargement of the object:
magnification
2 rules to minimize magnification include:
- 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 the object:
magnification
With magnification, the image shows the:
true shape of the object
If the distance of the source to the tooth is short, then the x-rays that interact with the tooth will be fairly ____ leading to ____.
divergent; greater magnification
If the distance of the source to the tooth is longer, then the x-rays in the beam that interact with the tooth will be more ____ leading to less ____.
parallel; magnification
Unequal enlargement:
distortion
Variation from tube shape of object:
distortion
Shape distortion has more to do with ___ than ___.
angles; distances
Unequal magnification of parts of an object:
distortion
Distortion can be caused by:
improper alignment of receptor, object, or beam
What are the rules for minimizing shape distortion? (2)
- 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 the object itself
foreshortening
Tooth is not parallel to the receptor and beam directed perpendicular can lead to what type of shape distortion? (2)
foreshortening & elongation
The radiographic image is longer than the object itself:
elongation
5 rules for accurate image formation:
- focal spot as small as possible
- source-object distance as long as possible (cone length)
- Object-receptor distance as short as possible (Film placement)
- object parallel to receptor (image receptor placement)
- beam perpindicular to object and receptor
Projection techniques for periodical radiography include: (2)
- paralleling technique: use long cone
- bisecting angle technique: use long or short cone
What are the two steps for the paralleling technique?
- receptor parallel to tooth
- beam perpendicular to tooth
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 are using the XCP correctly and you line up the beam with the cone, the x-ray beam will image:
entire area of interest (no cone cuts)
Cone cut shows up on the radiograph as:
white area
Getting a cone cut means you automatically have to retake the image (T/F)
False; as long as you obtain the area of interest
In a PA radiograph, we want ___ mm of bone around the apices
2-3mm (pretty sure)
If the contacts are open in the areas of interest this tells us that ____ angulation was correct
horizontal
The ____ technique is the preferred technique but the ____ technique may be used if the first choice technique does not work.
paralleling technique; bisecting angle technique
With he bisecting angle technique, you are not trying to get the image receptor parallel to the tooth, you are 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
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
The ____ technique has more limitations than the ____ technique
bisecting angle technique; paralleling technique
Why is the paralleling technique preferred technique over the bisecting angle technique?
a little more distortion with the bisecting angle technique
The bitewing is used to see:
crowns, inter proximal bone levels, alveolar bone support, caries, periodontal condition, calculus, 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 to us a ____ vertical angulation
slightly positive (+5 to10 degrees depending on location)
If the horizontal angulation is incorrect in the bitewing technique, then the image will display:
overlapping contacts
____ includes periapical and bitewing radiographs showing all teeth:
full mouth series
When viewing radiographs, what’s on the providers right is actually the patients:
left
Radiographic localization includes: (2)
- right angle method
- tube shift method (SLOB)
The right angle method states that:
if you take radiographs at right angles to each other of the areas of interest you can localize the area in question
If you take radiographs at right angles to each other of the areas of interest, you can localize the area in question:
right angle methodT
Same Lingual Opposite Buccal:
SLOB rule
Tube shift method may also be called:
SLOB rule
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
If the object moves in the same direction as what you moved the tubehead, then the object is ____ to the reference point (SAME)
lingual
If you take a straight on view of the premolars and you see the lesion apical to the apex, you rotate the tube head mesially, and the the lesion now moved distal to the apex of the tooth. This is the example of:
Opposite- buccal
The tube shift method technique, you can move the tube ___ or ____ on the second image.
mesially or distally (potentially even vertically)
First radiograph: supernumerary tooth overlapping the mesial of the root of the second molar
Move tube mesially
Second radiograph: the supernumerary tooth now does not overlap the mesial root of the second molar (shifted slightly mesial),
This means the lesion is:
lingual
SLOB stands for:
same lingual opposite buccal
shadow; the image of the object we receive
umbra
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
3 factors that affect the
