What are the benefits of IO radiographs ?
High spatial resolution.
Minimal superimposition of other anatomy.
Fast exposure.
Low radiation dose.
What are the disadvantages of IO radiographs ?
Limited to imaging of small area.
Relatively invasive and difficult technique.
What size of receptor is used for anterior PAs ?
Size 0
What size of receptor is used for bitewings and posterior PAs ?
Size 2
(4cm x 3cm)
What size of receptor is used for occlusal radiographs ?
Size 4
Define projection geometry.
Positioning (i.e. angulation and relative distances) of all of the components involved in taking radiograph.
Perfect projection geometry should result in fully accurate and undistorted image.
What are the 5 components of achieving best possible projection geometry ?
- Maintain sufficient focus-to-skin distance.
- Position receptor as close as reasonably possible to subject without bending receptor.
- Ensure receptor is stable in mouth.
- Use image receptor holders with a beam aiming device.
- Patient still.
What is the recommended focus to skin distance with spacer cone ?
At least 200mm for IO.
Measured from x-ray source.
What is the result of a longer fsd ?
Reduce magnification of image.
What is the shape of the x-ray beam in panoramic radiography ?
Narrow, vertical, fan-shaped.
How long does the image take in IO radiograph ?
0.2s
How long does the image take in panoramic radiograph ?
14s
Define focal trough.
Tomographic slice of interest - structures out with this area will appear faint and out of focus.
3 features of a ghost image.
- Ghost image appears horizontally magnified.
- Ghost image appears on contralateral side from actual structure.
- Ghost image appears superior to actual structure.
In panoramic radiograph structures are magnified - why ?
Divergence of x-ray beam.
In panoramic radiograph structures are magnified by around what % ?
25%
In panoramic radiograph structures lingual to the focal trough are magnified more or less ?
More.
And those buccal to focal trough are magnified less i.e. appear narrower.
Lingual to focal trough are magnified more and appear broader.
