Scatter Radiation and Grids

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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

KVP

The thicker the are the higher the _____needs to be

KvP

shorter the wavelength the better what

penetration power

the longer the wavelength more is what

absorbed

Generally anything measuring ____ produces enough scatter radiation to decrease the detail on the finished radiograph

>9cm

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

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

penumbra is

fogginess

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

horses

The best way to reduce scatter radiation is with the use of

Grids

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

radiodense

lead strips

radiolucent

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

higher

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 ___

mAs

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

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