Flashcards in Grids Deck (66):
Who built the 1st grid?
Dr. Gustav Bucky (1913)
What was Dr. Bucky's original principle?
Lead foil strips standing on edge separated by x-ray transparent interspacers
What is responsible for dark areas?
What is responsible for light areas?
Who came up with the moving grid?
Hollis Potter (1915-1917)
What is another name for a moving grid?
What was the idea behind the moving/ wire grid?
To get rid of grid lines
What was the problem with Potters grid?
-It was filtering out radiation before it got to the patient
-Required high technique to get through the grid
What was the Potter Bucky Diaphragm?
What determines when to use a grid?
1. When body part thickness exceeds 10cm
Ex: shoulders, knees
2. kVp is above 60
What is a grid composed of?
Alternating strips of radiopaque and radiolucent material
What type of material absorbs scatter?
What are the reasons lead is used as the typical radiopaque material?
-High atomic #
What material are the interspaces, radiolucent or radiopaque?
Is the interspace material typically thicker or thinner than lead?
What is often used as the interspace material?
*Plastic fiber can also be used
Why is aluminum often used as the interspace material?
- Absorbs low energy scatter
Why is aluminum used more frequently than plastic fiber as the interspace material?
Aluminum has a higher atomic number
What is grid ratio?
The ratio between the lead content and the aluminum content
Height of grid strip (h)
Interspace width (d)
If the height of the lead strips stays the same and the distance between them decreases, what is the result of the grid ratio?
What is the grid ratio when the lead strips are 3.2mm high and separated by 0.2mm?
----- = 16:1
If a grid ratio has an interspace of 0.5mm and lead strips that are 3mm high, what is it's grid ratio?
--- = 6:1
What is the grid ratio range?
4:1 - 16:1
*Mammo can go lower
Would a high grid ratio clean up more scatter radiation than a low grid ratio?
What would clean up scatter radiation better, a high or low grid ratio?
What type of grid ratio would improve contrast?
How does a high grid ratio clean up more scatter radiation?
It has more lead strips
What type of relationship exists between the distance between the lead strips and the grid ratio when the height of the grid strips stays the same?
The higher the ratio the ______ room you have before grid cut off?
When angling against a grid, do you have more room to play with on a 16:1 or an 8:1 grid ratio before you get grid cutoff?
How do you determine grid frequency?
By the number of lead strips per inch or cm
Do you have to be more accurate on a low or high grid ratio?
What is the most often seen grid frequency range?
Typically higher frequency grids have ________ lead strips.
Which one has a higher frequency, a 10 line grid or an 8 line grid?
10 line grid
Higher frequency with the same interspace distance reduces what?
The grid effectiveness
What are the most common grid ratio's?
How much cleanup will a 5:1 grid ratio give?
How much cleanup will a 16:1 grid ratio give?
The higher the grid ratio the _______ cleanup.
What material is the most important in determining grid efficiency?
Lead content is greater in a grid with a...
High grid ratio
As lead increases what happens?
Contrast increases and scatter decreases
Parallel grids clean up scatter in how many directions?
What cleans up scatter better, a parallel grid or a crossed grid?
Which grid has more potential for grid cutoff, parallel or cross?
To be most effective, where must the CR be placed on a Crossed grid?
In the center
How many directions does a cross grid clean up scatter?
What kind of grid has lead strips that are angled to match the divergence of the beam?
What type of grid requires a specific SID to minimize grid cut off or absorption?
What type of grids are more difficult to manufacture?
What are the (3) things to remember with focused grids?
Do grids move during exposure?
In a reciprocating or oscillating pattern
What type of grid movement is described as; motor driven back and forth movement (@2cm)?
What type of grid movement is described as; circular movement?
Oscillating (like a pinball)
What are the two types of grid movement?
Reciprocating & Oscillating
What is the down side of a moving grid?
Creates image blur
Creating more OID
What is Selectivity or the "K" factor?
The ability to allow primary radiation to reach the image receptor and prevent scatter
Grids are designed to absorb scatter radiation, but they sometimes...
Absorb primary radiation
Typically "K" factor ranges between...
1.5- 3.5 (1.5- 3.5 times better when grids are used)
What does the "K" factor compare?
Contrast of an image with a grid to one without a grid
What is the Contrast Improvement Factor?
Contrast w/ grid
Contrast w/o grid
What are factors when selecting a grid?
As grid ratio increases, radigraphic density decreases; as grid ratio decreases...
radiographic density increases
Below 90 kVp, you can use grid ratio's up to...