Grids Part II Flashcards by Mat Doss

As grid ratio goes up…

Density goes down

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What is another name for the GCF (Grid Conversion Factor?)

Bucky Factor

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What is the GCF used for?

When changing from one grid ratio to another

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What is the Grid Conversion Factor formula?

mAs w/o grid

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What is the Grid Ratio & GCF chart?

Grid Ratio GCF

5: 1 2
6: 1 3
8: 1 4
12: 1 5
16: 1 6

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What is the formula for increasing the grid ratio?

mAs1 = GCF1
—— ——-
mAs2 GCF2

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If you increase grid ratio, will mAs go up or down?

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It is important to remember that patient dose is increased when…

Using a grid compared with not using a grid

- Using a higher grid ratio

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What is the biggest problem when using grids?

Misalignment (increased OID as well)

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Define

Grid Errors: Off Level

Grid is tilted
Could be because of detent

Results in:

Cutoff across entire image
Light image
Halo effect

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Grid Errors:

Off Center

-Out of Lateral

Results in:
-Decreased density across entire image

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Grid Errors:

Off Focus

-Improper SID

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Grid Errors:

Upside Down Grid

Results in:

Cut off edges of film

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Grid Errors:

Off center & Off focus

-Seen in portables

Results in:

Uneven exposure
Dark on one side, light on the other

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What are some factors that increase scatter radiation?

Improper technique (low)
Poor position
Collimation
Cassette size
Lack of lead strips

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A higher quality grid can attenuate how much scatter radiation?

80-90%

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What are (3) factors that contribute to an increase in scatter?

Increased:

kVp
x-ray field size
patient thickness

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Proper collimation has the primary effect of reducing…

Patient dose by reducing scatter

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What is the Air Gap Technique?

Compensating for not using a grid

- Creating a gap where scatter can escape

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What are disadvantages of using an Air Gap Technique?

Magnification
Image blur from OID
Patient dose

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How much gap do you use in an Air Gap Technique

Receptor is 10-15 cm from patient
By doing this, ideally scatter is not detected
Contrast is enhanced

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How much increase in technique do you need for an Air Gap Technique?

10% increase per cm

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Using an Air Gap Technique, the 10cm is equivalent to what ratio grid…

15:1

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A grid has the following characteristics: grid ratio = 10:1, grid height = 4.5mm; grid strip width = 40 um; interspace width = 450 um. What is the grid frequency

20 lines/cm

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Statement: | All of the following are true about scattered radiation:

- Puts density on the film - Travels in a different direction from primary radiation - Has less energy that primary radiation

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 14 Original Grid = 5:1 New Grid 16:1

14 2 ___ = ___ x= 42 x 6

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 40 Original Grid = 6:1 New Grid 12:1

66.6

The spaces between the lead strips of a grid are called:

Interspaces

A grid that has strips that are .120 inch high and interspaces that are .010 inch wide has a grid ratio of:

12:1

The use of a grid on a radiograph has what effect on contrast?

It increases it

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 12 Original Grid = 8:1 New Grid = None

3 mAs

The most common type of grid pattern is crossed?

True

The purpose of moving the grid with the Bucky is:

Blur the grid lines

Which grid ratio will absorb the most scattered radiation 8:1 or 12:1?

12:1

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 40 Original Grid = 5:1 New Grid = 8:1

Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 15 Original Grid = 16:1 New Grid = 6:1

7.5

The presence of a large amount of scattered radiation on the radiograph has what effect on contrast?

Decreases it

As the grid ratio increases, there is also an increase in what?

Contrast improvement factor

The name of the man who invented the grid is:

Gustave Bucky

Unwanted absorption of primary radiation by the grid is the definition of:

Grid cut-off

The minimum kVp that requires the use of a grid is:

The number of grid lines per inch is the definition of:

Grid frequency

The height of the lead strips compared to the distance between the lead strips is the definition of:

Grid ratio

What is the purpose of a grid?

Absorb scatter and allow primary radiation to pass through

Which of the following is not a grid positioning error? - Air gap grid - Lateral decentering - Off-center grid - Off-focus grid - Off-level grid

Air Gap Grid

The focused grid pattern most closely matches the way the xray beam emerges from the tube?

True

Which grid pattern will clean up the most scattered radiation?

Crossed

What percentage of change in kVp is roughly equal to doubling the mAs?

What happens to density as SID increases?

Decreases

All other factors remaining constant, a switch to a slower screen will have what effect on density?

Decrease

What happens to density when a grid is introduced into the system?

Decreases

What happens to density with increases in filtration?

Decreases

What happens to density with decreases in tissue thickness?

Increases

A grid should be used if the body part measures more than:

10 cm

What is contrast controlled by?

kVp

A grid will decrease scatter production?

False Scatter production takes place in the patient. A grid will reduce the amount that reaches the receptor.

Collimation has what effect on image contrast?

Increases contrast

What is density controlled by?

mAs

What is the result in density after collimating?

Density will decrease

mA and Density are _____ proportional

Directly

Time and Density are _____ proportional

Directly

mAs controls _____.

Density

SID and Density are _____ proportional

Inversely

OID and Density are ____ proportional because of the air gap

Inversely

Focal spot size only effects _____ _____.

Recorded Detail

A grid with a higher ratio contains more lead and reduces _____.

Density

A larger collimation field size produces more scatter radiation and therefore more _____.

Density

An increase in filtration _____ the amount of radiation in the beam

Reduces

A higher speed screen will produce more light and more _____.

Density

Developer temperature and Density are _____ proportional.

Directly

Grids Part II Flashcards

(70 cards)