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Density is directly related to the quantity of x-rays produced (mAS)
Different densities (black and white). High contrast (short scale) very white and very black; low contrast (long scale) more shades of gray.
What is contrast inversely related to?
What happens to contrast kV is increased?
Decrease contrast/ more grays
What happens to contrast kV is decreased?
Increased contrast/ more black and white
What do geometric factors include?
- Focal spot size
- xray machine alignment
- patient placement
Misrepresentation of the size or shape of an object.
Degree of film sharpness
How do you improve detail?
- Smaller focal spot
- Increase FFD
- Decreased OFD
- patient positioning
- machine alignment
- shorter exposure time
Area of unsharpness or fuzziness
What happens when penumbra is increased?
- Larger focal spot size
- lack of collimation
- decrease FFD
- increase OFD
The purpose of exposing the film (the useful beam).
* Scatter radiation
Secondary radiation produced by an absorber (body), produced film fog.
FFD Focal Film Distance
(Also TFD, SID, SFD) Distance between the focal spot and the film.
If you increase FFD what happens?
OFD Object Film Distance
Always decrease as much that is practical to decrease magnification.
Inverse square law
The intensity of the radiation varies inversely with the square of the distance.
Inverse square law: what happens if you double the distance (FFD)?
Decrease of intensity of the radiation to 1/4 and requires a compensatory increase of the mAs by 4x's.
Anode heel effect
- Due to the angle (bevel) intensity.
- INCREASES slowly towards CATHODE; and DECREASES rapidly towards the ANODE.
Air gap technique
Reducing scatter radiation. between 10-15cm from the film.
What is the disadvantage of the air gap technique?
converting AC current to DC current
Increase kVp by 15% double the mAs.
Bone deposition occurs along the lines of increased mechanical stress.
Pressure on a growth plate retards the rate of growth, traction accelerates.
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