intraoral imaging technique Flashcards
GEOMETRIC CHARACTERISTICS
- Image sharpness
- Image magnification
- Image shape distortion
Unsharpness
Fuzzy, unsharp margin of
radiographic image.
Due to Penumbra or edge gradient from photons interacting at the objects edge
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.
how does a small radiation source produce sharper images, can we control this?
fewer photons at the edge of the object= smaller pneumbra
Out of our control, up to manufacturer
increased source to object distance effect, can we control this?
results in more parallel photons at the edge of the object, would be more divergent if distance shorter causing a larger pneumbra
can be controlled with cone length
object to receptor distance, can we control?
want it to be short to decrease divergence of photons from object edge to receptor= decreased pneumbra
controlled with receptor placement
MAGNIFICATION (Equal Enlargement)
Enlargement of radiographic image, compared to actual size of object. Image shows true shape of object
2 Rules to Minimize Magnification
Rule #1.
Source-to-object distance should be as long as possible.
Rule #2
Source-to-receptor distance should be as short as possible.
long source to object distance for magnification
reduces divergence of photons
short object to receptor distance for magnification
reduces photon divergence from object to receptor
5 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
PROJECTION TECHNIQUES FOR PERIAPICAL RADIOGRAPHY
1. Paralleling Technique – use long cone
2. Bisecting Angle Technique – use long or short cone
2 Rules to Minimize Distortion
Rule #1:
Object and receptor should be parallel.
Rule #2:
Beam should be perpendicular to object and receptor.
PARALLELING TECHNIQUE
PARALLELING TECHNIQUE
1. Receptor parallel to tooth: must also get apices
increased object-receptor distance can be offset with increased source-receptor distance (long cone)
2. Beam perpendicular to tooth/receptor.
alignment of beam and receptor, if not done?
if not done will result in a cone cut
what is the preffered imaging method? if it cannot be done what is used?
Paralleling technique is the preferred method.
If the paralleling technique cannot be used, the bisecting angle technique may be used.
BISECTING ANGLE TECHNIQUE Based on
Based on Rule of Isometry:
If two triangles have two equal angles and a
common side, then the two triangles are equal.
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.
PROJECTION ERRORS IN PERIAPICAL RADIOGRAPHY
Vertical Angulation
Horizontal Angulation
Alignment of Beam and Receptor
FORESHORTENING due to?
Tooth not parallel to receptor, and beam directed perpendicular to receptor.
results in tooth appearing shorter than is actually is
ELONGATION due to?
.
Tooth not parallel to receptor, and beam directed perpendicular to tooth.
results in tooth appearing longer than it actually is
Improper horizontal
angulation results in?
overlapping of contacts.
Improper alignment of
beam and receptor results
in?
Improper alignment of
beam and receptor results
in cone cutting.
what do we want to see with BWs
Crowns, open interproximal areas and alveolar bone support, Caries, periodontal condition, calculus, crown margins
BW angulation
slight + angulation of the source due to curve of wilson
BW HA errors? when to retake
results in overlapped contacts retake it half the enamel thickness is overlapped
methods of localization
- Right angle method
- Tube shift method (SLOB)
Buccal object rule
Right Angle
Method of localization
two radiographs are taken with the receptors perpindicular to one another
ex: PA and occlusal
Tube Shift Method
take a normal PA then shift the tube in a M or D direction for another PA
if the object moves with the tube: lingual
if object moves in opposite: buccal
