Density 2 Flashcards
What concept is occurring when a 10 MeV x-ray invades a nucleus?
Photodisintegration
What happens to the energy during photo disintegration?
Is absorbed by the nucleus and nuclear fragments are emitted
What type of conditions contribute to scatter radiation production?
1 high kVp
2 thick soft tissue (water density)
3 large field size
What is the solution for a large field size that has the potential to produce a lot of scatter?
Collimation
What are some scatter control methods?
1 optimum kVp 2 collimation to control field size 3 air-gap technique 4 scatter-absorbing grids 5 recumbent radiography
What is probably the best way to take an x-ray of a larger patient to ultimately reduce overall scatter?
Take it recumbent
What kind of filter is a grid?
Selective lead filter (between patient and film)
Who invented the scatter-absorbing grid?
Gustave Bucky in 1913
When is a grid needed?
When patient part measures greater than 10cm or when using techniques above 70 kVp
How does the grid affect the appearance of the film?
Improves contrast
What specific benefit does the grid NOT have?
Does NOT protect the patient
What is the orientation of the lead lines found in a grid?
Linear***, crosshatched, or rhombic crosshatched pattern
What separates the thin lead lines of the grid?
Thin strips of aluminum or carbon fiber
What are the two types of a linear grid?
Parallel and focused
Which type of grid design involves a grid cut-off and an underexposed appearance of the film?
Parallel
What is the benefit of a focused grid?
Grid cut-off is eliminated
What is the grid ratio?
Measure of the height of the lead strips divided by the distance between them (h/d)
When there is an increased grid ratio, what measurement must be increased to compensate?
mAs
How does a higher grid ratio affect contrast?
Higher contrast
What is the recommended grid ratio?
12: 1 focused grid used with a single phase generator
10: 1 focused grid used with high frequency generator
What is grid frequency?
Measure of the number of lead lines per inch or centimeter
What is the downside to a higher grid frequency?
Patient dose increases
What is the benefit to a higher grid frequency?
Less grid lines on film
How does the removal of scatter by a grid affect film density?
Decreases it (lighter film)
If the film appears too light when using a grid to remove scatter, what measurement must be changed to compensate?
Increase mAs (to increase density)
How does an increase in grid ratio affect film density?
Decreases it (lighter film)
What effect does decreased film size have on density and why?
Decreased density (because scatter is eliminated)
If you take a 14 x 17 and change it to a 5x5 via collimation, how is the appearance of the film changed?
Lighter film (decreased density)
What is spot filming?
Using smaller films and tight collimation to improve contrast
What technique can be a substitute for a grid?
Air-gap technique
How big of an air-gap is comparable to a 7:1 grid ratio in a scatter clean-up?
4”-6”
Why is the air-gap technique not recommended?
Changes must be then be made to technique, tube placement, etc.
The air gap produces what kind of contrast: short or long scale?
Short scale
What is the maximum distance for an air-gap due to magnification?
10”
How does laying a patient recumbent prevent scatter?
Decreases diameter of the patient (lower kVp and mAs needed)
What is the purpose of compression bands?
Compression of tissues to reduce scatter and improve contrast
What is the purpose of lead vinyl blockers?
Cover areas of film on film cassettes where multiple exposures are made on a single film
