Flashcards in Grids Part II Deck (70):
As grid ratio goes up...
Density goes down
What is another name for the GCF (Grid Conversion Factor?)
What is the GCF used for?
When changing from one grid ratio to another
What is the Grid Conversion Factor formula?
mAs w/o grid
What is the Grid Ratio & GCF chart?
Grid Ratio GCF
What is the formula for increasing the grid ratio?
mAs1 = GCF1
If you increase grid ratio, will mAs go up or down?
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
What is the biggest problem when using grids?
Misalignment (increased OID as well)
Grid Errors: Off Level
-Grid is tilted
-Could be because of detent
-Cutoff across entire image
-Out of Lateral
-Decreased density across entire image
Upside Down Grid
Cut off edges of film
Off center & Off focus
-Seen in portables
-Dark on one side, light on the other
What are some factors that increase scatter radiation?
-Improper technique (low)
-Lack of lead strips
A higher quality grid can attenuate how much scatter radiation?
What are (3) factors that contribute to an increase in scatter?
-x-ray field size
Proper collimation has the primary effect of reducing...
Patient dose by reducing scatter
What is the Air Gap Technique?
-Compensating for not using a grid
-Creating a gap where scatter can escape
What are disadvantages of using an Air Gap Technique?
-Image blur from OID
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
How much increase in technique do you need for an Air Gap Technique?
10% increase per cm
Using an Air Gap Technique, the 10cm is equivalent to what ratio grid...
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
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
___ = ___ x= 42
Calculate the new mAs to be used with the following grid ratio changes. Original mAs = 40 Original Grid = 6:1 New Grid 12:1
The spaces between the lead strips of a grid are called:
A grid that has strips that are .120 inch high and interspaces that are .010 inch wide has a grid ratio of:
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
The most common type of grid pattern is crossed?
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?
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
The presence of a large amount of scattered radiation on the radiograph has what effect on contrast?
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:
Unwanted absorption of primary radiation by the grid is the definition of:
The minimum kVp that requires the use of a grid is:
The number of grid lines per inch is the definition of:
The height of the lead strips compared to the distance between the lead strips is the definition of:
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
Air Gap Grid
The focused grid pattern most closely matches the way the xray beam emerges from the tube?
Which grid pattern will clean up the most scattered radiation?
What percentage of change in kVp is roughly equal to doubling the mAs?
What happens to density as SID increases?
All other factors remaining constant, a switch to a slower screen will have what effect on density?
What happens to density when a grid is introduced into the system?
What happens to density with increases in filtration?
What happens to density with decreases in tissue thickness?
A grid should be used if the body part measures more than:
What is contrast controlled by?
A grid will decrease scatter production?
Scatter production takes place in the patient. A grid will reduce the amount that reaches the receptor.
Collimation has what effect on image contrast?
What is density controlled by?
What is the result in density after collimating?
Density will decrease
mA and Density are _____ proportional
Time and Density are _____ proportional
mAs controls _____.
SID and Density are _____ proportional
OID and Density are ____ proportional because of the air gap
Focal spot size only effects _____ _____.
A grid with a higher ratio contains more lead and reduces _____.
A larger collimation field size produces more scatter radiation and therefore more _____.
An increase in filtration _____ the amount of radiation in the beam
A higher speed screen will produce more light and more _____.