Unit 4 (Grids)
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Unit 4 (Grids)
Unit 4: Chapter 18 (Grids)
What are the two main purposes of a grid?
Is absorption or transmission responsible for the dark areas of the radiograph?
If you use a grid without compensating by increasing technical factors, will the density increase or decrease?
What is defined as a process in which x-rays interact and change direction?
Name two things scatter can produce?
As kVp increases, does scatter increase or decrease?
If the field size decreases, does the scatter increase or decrease?
As the thickness of the part decreases, does the scatter increase or decrease?
If the atomic number decreases, does the scatter increase or decrease?
You should consider using a grid when the part thickness is:
greater than 10cm
Would a KUB or a hand produce a greater amount of scatter?
Consider using a grid if you use a kVp:
greater than 60
What is the most common metal that interspace material is made of?
Name the two main components of grid construction.
radiopaque lead strips
radioluscent interspace material
Who created grids and when?
Dr. Gustav Bucky
Name three types of lead strip positioning.
Which grid produces the maximum amount of scatter?
A. linear parallel
B. cross hatched
C. linear focused
B. cross hatched
(this multiple choice question has been scrambled)
Grids allow ____________ to reach the IR.
Name the two largest disadvantages of grid use?
increase in patient dose
grid lines on film
Who made improvments to the use of grids?
Dr. Hollis Potter
How did Dr. Potter improve the use of grids?
realigned lead strips to run in one direction
moved grid during exposure to make lines invisibile on image
When considering grid dimensions, "h" stands for:
height of radiopaque strips
When considering grid dimensions, "D" stands for:
distance between the strips (thickness of interspace material)
What is the grid ratio formula?
grid ratio = h/D
Does a higher grid ratio mean more or less lead content?
Is a higher grid ratio more or less efficient in removing scatter?
What is the typical grid ratio range?
5:1 to 16:1
What is defined as the number of lead strips per inch or cm?
Common frequency ranges:
Typically, higher frequency grids have thicker or thinner lead strips?
Do thicker lines result in more or less grid clean-up?
Do grid ratio and frequency have a direct or indirect relationship?
Digital imaging systems can use very high frequency grids with ranges of:
What is the most important factor in a grid's efficiency?
What unit is used to measure lead content of a grid?
mass per unit area (g/cm
What type of grid tends to have the highest lead content?
high ratio, low frequency grid
As lead content increases, does contrast increase or decrease?
How are the lead strips of a cross hatched grid pattern positioned?
both horizontal and vertical strips
Name two positioning requirements when using a cross hatched grid.
primary beam must be centered to grid
grid must remain flat
How are the lead strips of a linear grid pattern positioned?
the lead strips run the length of the cassette
Name the two types of linear grids?
In a focused linear grid, lead strips are angled to match the __________ of the beam.
When using a focused linear grid, the primary beam will align with the:
interspace material (scatter absorbed by lead strips)
What type of positioning lattitude does a focused linear grid have?
Name three aspects of narrow positioning lattitude.
improper centering results in peripheral cut-off
only useful at preset SID
higher ratio grid require careful alignment with tube
Improper centering results in:
A parallel linear grid absorbs a large amount of _____________ resulting in ____________.
Type of grid that can be attached to a cassette for use:
stationary grid (aka grid caps)
What size is the Potter-Bucky diaphragm grid?
Name two types of grid movement.
Describe a reciprocating motor.
a motor that drives the grid back and forth during exposure.
Describe the movement of an oscillating grid.
moves in a circular motion.
When a grid is placed in the beam to remove scatter, will the density of the radiograph increase or decrease?
What formula is used to find the grid conversion factor or Bucky factor?
GCF = mAs with grid/ mAs without grid
In the grid conversion formula, are you dealing with a direct or indirect relationship between mAs and GCF?
Who evaluates grid performance?
International Commission on Radiologic Units and Measurements (ICRU)
What two criteria are used by the ICRU to evaluate grid performance?
contrast improvment ability
What describes the grids ability to allow primary radiation to reach the IR and prevent scatter?
Are highly selective grids better or worse at removing scattered radiation?
High lead content grids are more or less selective?
What compares radiographic contrast of an image with a grid to radiographic contrast of an image without a grid?
contrast improvement ability (the K factor)
What are the typical ranges of the K factor?
The higher the K factor number, the higher or lower the contrast?
If you are dealing with the capital letter K, you are dealing with:
Proper ___________ between x-ray tube and grid is very important.
Improper alignment will result in:
The grid error off-level refers to:
the receptor itself
The grid error off-center refers to:
the central ray
The grid error off-focus refers to:
angulation of the tube
Name five common grid errors.
Which grid error is a result of not being lined up with the convergence point?
Where will you see cut-off with an off-level grid?
on the peripheral edges
Which grid error affects one side of the image more than the other?
What is the Moire effect and how can it be prevented?
when grid lines are parallel to scan lines (digital systems)
high frequency grids can prevent it
What is an alternative to grid use?
A 10" air-gap has a similar clean-up of what grid ratio?
What amount of air-gap is needed for a clean-up similiar to a 15:1 grid?