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67 Cards in this Set

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In relation to the patient and image receptor, where are grids located?
between the patient and the IR
Describe effects of Grid use on radiograph.
Grids absorb scatter radiation; reduces radiographic density, radiographs will have higher contrast, less gray, be less fogged and have shorter scale contrast
How do grids help improve image quality?
Improve image quality by "cleaning up' scattered radiation. Visibility factor.
Grids improve VISIBILITY
Are grids useful in patient protection?
NO
List some methods to reduce scattered radiation reaching the IR
Use lowest acceptable kVP for each body part, always collimate to the smallest possible field, Compress the part if possible, use a grid.
When should a grid be used?
When radiographing thicker body parts, and measuring > 10 - 12cm,/or using higher kVp > 60
If you choose to use a grid, what technique will have to change?
You will have to increase mAs accordingly.
What effect will using a grid have on patient dose?
mAs is directly proportional to patient dose. If mAs is doubled, patient Dose will be doubled
Grid Material
very thin lead stips. Lead strips absorb or "clean up" most of the scattered xrays.
Lead has a high atomic Z number.
Interspace Material
made of plastic, aluminum, carbon fiber or other radiolucent. Interspace material will have a low atomic Z number.
State purpose of grid Aluminum covering.
to provide structure and protection
Describe disadvantage of using grids
Requires higher mAs exposure factors, which increases patient dose, Requires more precise positioning skills
Describe advantage of using grids
* Improves image quality by reducing the amount of scattered xrays reaching the IR
* Grids help "clean up" scattered radiation
List types of grids
Linear Focused
Linear Non-focused or parallel
Cross hatch
* linear focused is the most common
Linear Non-focused or Parallel Grid
The grid strips are straight up and down and not angled to match the divergent xray beam.
Not used often, will always "cut-off" some of the useful, image=forming xrays, especially @ shorter SID's
In relation to the patient and image receptor, where are grids located?
between the patient and the IR
Describe effects of Grid use on radiograph.
Grids absorb scatter radiation; reduces radiographic density, radiographs will have higher contrast, less gray, be less fogged and have shorter scale contrast
How do grids help improve image quality?
Improve image quality by "cleaning up' scattered radiation. Visibility factor.
Grids improve VISIBILITY
Are grids useful in patient protection?
NO
List some methods to reduce scattered radiation reaching the IR
Use lowest acceptable kVP for each body part, always collimate to the smallest possible field, Compress the part if possible, use a grid.
When should a grid be used?
When radiographing thicker body parts, and measuring > 10 - 12cm,/or using higher kVp > 60
If you choose to use a grid, what technique will have to change?
You will have to increase mAs accordingly.
What effect will using a grid have on patient dose?
mAs is directly proportional to patient dose. If mAs is doubled, patient Dose will be doubled
Grid Material
very thin lead stips. Lead strips absorb or "clean up" most of the scattered xrays.
Lead has a high atomic Z number.
Interspace Material
made of plastic, aluminum, carbon fiber or other radiolucent. Interspace material will have a low atomic Z number.
State purpose of grid Aluminum covering.
to provide structure and protection
Describe disadvantage of using grids
Requires higher mAs exposure factors, which increases patient dose, Requires more precise positioning skills
Describe advantage of using grids
* Improves image quality by reducing the amount of scattered xrays reaching the IR
* Grids help "clean up" scattered radiation
List types of grids
Linear Focused
Linear Non-focused or parallel
Cross hatch
* linear focused is the most common
Linear Non-focused or Parallel Grid
The grid strips are straight up and down and not angled to match the divergent xray beam.
Not used often, will always "cut-off" some of the useful, image=forming xrays, especially @ shorter SID's
Linear Focused Grid
*Lead strips are angled to coincide with the divergent xray beam
*Grid will have a designated "tube side" like an IR
* all linear focused grids will have a designated "focusing distance" between them.
Parallel Non-focused grids best used with what type of SID?
Longer SID
List factors that increase scatter radiation
increases in patient thickness, larger field sizes, decreases in atomic number of tissue
First Grid
1913
American! radiologist Gustav Bucky (crosshatch)
Improved Grid
1920 Hollis Potter
Chicago radiologist
* realigned lead strip in one direction
redesigned "Potter-Bucky diagpragm" which allowed grid to move during exposure..therefore not visible on image.
Grid Ratio
defined as ratio of height of the lead strips to the distance between the strips GR = h/D
Grid Ratio
affects the amount of scatter absorbed by determining the maximum angle of a scattered ray that can get through the grid. The smaller the angle, the less scatter reaches the image receptor
Grid Ratio
H/D , inverse relationship between distance between lead strips and grid ratio when height remains the same. > grid ratio < scatter; < grid ratio > scatter
Grid Frequency or
Strip Density
the number of grid lines per inch (states on a grid as the LPI (lines per inch)
Reciprocating Grid
Bucky & Chest Board: Move during the exposure
Stationary Grids
Do not move.. Taped in place on the cassette or IR
Cross Hatch grid
* Incorporated in fluoroscopic IR
* is actually 2 parallel grids placed on top of each other at right angles
*Clean up > Scatter BUT
CAN NOT ANGLE the beam
Grid Cutoff
Undesirable absorption of the useful, image-forming xrays by the grid strips.
How does grid cut off happen
By improper alignment of the grid to the central ray
How does grid cut off effect the image?
The image will appear underexposed and grid strips are visible.
List types of grid cutoff
*Off Near Focus or Off Far focus
*Off Level
*Focused Grid Upside Down
*Off Center
*Angling Against Grid Lines
Off Near Focus / Off Far Focus
Grid Cut Off
when SID is longer or shorter than the recommended grid focusing distance // Closer is more critical than far
Off Level
Grid Cut Off
grid not level and causes xray beam to go "against" grid line. usually portable hip grid sinks into soft mattress/off level to xray beam
Focused grid upside down
Grid Cut Off
obvious cutoff artifact.. you need to always place the "tube side" of the grid to the xray tube.
Off Center
Grid Cut Off
CR not centered to grid
Angling against Grid lines
Grid Cut Off
Angle xray beam across a grid and not with the grid. Cut off identical to off-level cut-off
Common Grid Ratios
5:1, 6:1, 8:1, 10:1, 12:1, 16:1

10:1 and 12:1 considered the same
Grid Focusing Distance
recommended SID range for a grid
Higher Grid Ratio compared to a lower grid ratio
Heavier, thicker, better clean up, requires more precise positioning of CR to grid. < Positioning latitude
When should you select a higher grid ratio?
* When you have a really big patient
* When you use 120 kVp or >
* When max cleanup of scattered radition is required
When should you select a lower grid ratio?
When you need > positioning latitute - trauma or portables
When max clean up not so important
What type of Grid is usually found in the Bucky?
* Usually 8:1, 10:1 or 12:1, linear focused
* And it reciprocates
Density Maintenance Grid Factors
5:1 - 2
6:1 - 3
8:1 - 4
10:1 and 12:1 - 5
16:1 - 6
Air Gap Technique
* An option to grid use on certain exams
Air Gap Technique
uses OID instead of a grid to reduce the intensity of scattered radiation reaching the IR
Air Gap Technique
By using air gap technique, some of the scattered photons will miss hitting the IR because of the physical distance between patient and IR
Air Gap Technique
The increased OID requires a 72" SID to help reduce magnification
Possible applications of Air Gap Technique today
Lateral C-Spine
DCBE Decubs
*Patient needs to be an average or small size (thickness) for air gap to work
*Air gap requires that you strictly collimate the xray to the exact size of the IR
Bucky or Bucky Tray
if bucky used, increase OID = magnification of anatomy. Generally 3-4 inch distance between table top and bucky tray
Grids influence which radiographic properties
Contrast and Density
Grids have NO effect on which radiographic property
Recorded Details
Most important grid factor
Grid Ratio