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Scatter Radiation and Grids

What will an x-ray do when it enters a patient's body?(3)
1. penetrate
2. be absorbed
3. produce scatter radiation
Scatter radiation is also called what?
secondary radiation
Scatter radiation disadvantages(4)
1. film fogging
2. decreases overall contrast
3. increases scale of contrast to a non-diagnostic level
4. causes safety hazards
decreased contrast makes what harder to see
subtle lesions, detail of tissue interfaces
The higher the _____value is the more scatter radiation is produced
The thicker the are the higher the _____needs to be
shorter the wavelength the better what
penetration power
the longer the wavelength more is what
Generally anything measuring ____ produces enough scatter radiation to decrease the detail on the finished radiograph
Three main ways to decrease scatter
1. beam limiting devices
2. air gap technique
3. grids
Beam limiting devices include(4)
1. cones
2. diaphrams
3. collimators
4. aluminum filters
beam limiting devices do what
confine beam to only the area being examined, decreases the amount of tissue being irradiated
Cones are made of what and placed where to do what
lead cylinders of fixed sizes and placed over the xray tube to restrict the size of the primary beam to the size of the cone(round area)
Diaphragms are made of what placed where and come in what shapes
come in fixed sizes, are made of lead, placed on the tube head near the tube window, rectangular, circular, square
Which limiting device is the most efficient?
Collimators are placed where by who
on tube head by the manufacturer
collimators are what and come with what, why
adjustable and come with a light for visualization of the actual size/area of the primary beam
aluminum filters are placed where and what is their function
over x-ray tube window, absorbs less penetrating xrays directly from primary beam
Air Gap technique OFD is increased from _ to _in, why
0 to 6 to reduce amount of scatter that will reach the film
An increase OFD causes an increase of what on the film
penumbra is
How do you decrease penumbra?
increase the FFD from 48 to 72 in
When you increase FFD what will happen to mAs?
mAs will need to be increased
air gap technique is most useful with what species
The best way to reduce scatter radiation is with the use of
Grids do what
enhance the overall contrast and scale of contrast on the finished radiograph
Grids are used when imaging areas greater than____ and they decrease____ and increase____
10 cm, scatter, contrast
lead strips
plastic strips
3 variables that determine grid effectiveness are
1. placement of strips
2. height of the strips
3. number of lines per inch
Grids absorb scatter radiation but unfortunately also absorb what
a large amount of the primary beam
only the xrays that can pass through ____ in perfect _____will expose the film
the plastic strips, alignment
what can be done to compensate for the absorption loss from grid use
increase the mAs
the efficiency of the grid depends upon what
the grid ratio
grid ratio definition
the relationship of the height of the lead strips to the width between them
The _____ the grid ration, the more efficient the grud is at absorbing scatter
Two types of Grids
1. parallel
2. focused
Two configuration of Grids
1. Linear
2. Crossed
Most efficient combo of grid
focused crossed
Grid lines are caused by what
areas of primary beam being absorbed by the lead strips in the grid
3 ways to eliminate grid lines
1. increase the number of lines per inch
2. use thin lead strips
3. use a potter-buck mechanism
the more lines per inch the fewer what
grid lines are visible on the finished radiograph
Bucky potter mechanism works how
sets grid in motion to blur the lines, a tray is placed beneath the bucky to hold the cassette, when an exposure is made the bucky will move the grid against the grid lines
where is the bucky potter mechanism located
suspended in a thin cabinet beneath the x-ray table
with a bucky you can have a grid with fewer lines per inc which allows you to have a lower ___
causes for visible grid lines(4)
1. exposure made before or after the bucky movement occurs
2. uneven or irregular bucky movement of the grid
3. if the grid and x ray tube are not centered with each other
4. if the grid is not perpendicular to the tube