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67 Cards in this Set
- Front
- Back
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In relation to the patient and image receptor, where are grids located?
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between the patient and the IR
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Describe effects of Grid use on radiograph.
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Grids absorb scatter radiation; reduces radiographic density, radiographs will have higher contrast, less gray, be less fogged and have shorter scale contrast
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How do grids help improve image quality?
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Improve image quality by "cleaning up' scattered radiation. Visibility factor.
Grids improve VISIBILITY |
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Are grids useful in patient protection?
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NO
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List some methods to reduce scattered radiation reaching the IR
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Use lowest acceptable kVP for each body part, always collimate to the smallest possible field, Compress the part if possible, use a grid.
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When should a grid be used?
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When radiographing thicker body parts, and measuring > 10 - 12cm,/or using higher kVp > 60
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If you choose to use a grid, what technique will have to change?
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You will have to increase mAs accordingly.
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What effect will using a grid have on patient dose?
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mAs is directly proportional to patient dose. If mAs is doubled, patient Dose will be doubled
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Grid Material
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very thin lead stips. Lead strips absorb or "clean up" most of the scattered xrays.
Lead has a high atomic Z number. |
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Interspace Material
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made of plastic, aluminum, carbon fiber or other radiolucent. Interspace material will have a low atomic Z number.
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State purpose of grid Aluminum covering.
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to provide structure and protection
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Describe disadvantage of using grids
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Requires higher mAs exposure factors, which increases patient dose, Requires more precise positioning skills
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Describe advantage of using grids
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* Improves image quality by reducing the amount of scattered xrays reaching the IR
* Grids help "clean up" scattered radiation |
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List types of grids
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Linear Focused
Linear Non-focused or parallel Cross hatch * linear focused is the most common |
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Linear Non-focused or Parallel Grid
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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 |
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In relation to the patient and image receptor, where are grids located?
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between the patient and the IR
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Describe effects of Grid use on radiograph.
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Grids absorb scatter radiation; reduces radiographic density, radiographs will have higher contrast, less gray, be less fogged and have shorter scale contrast
|
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How do grids help improve image quality?
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Improve image quality by "cleaning up' scattered radiation. Visibility factor.
Grids improve VISIBILITY |
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Are grids useful in patient protection?
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NO
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List some methods to reduce scattered radiation reaching the IR
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Use lowest acceptable kVP for each body part, always collimate to the smallest possible field, Compress the part if possible, use a grid.
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When should a grid be used?
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When radiographing thicker body parts, and measuring > 10 - 12cm,/or using higher kVp > 60
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If you choose to use a grid, what technique will have to change?
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You will have to increase mAs accordingly.
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What effect will using a grid have on patient dose?
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mAs is directly proportional to patient dose. If mAs is doubled, patient Dose will be doubled
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Grid Material
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very thin lead stips. Lead strips absorb or "clean up" most of the scattered xrays.
Lead has a high atomic Z number. |
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Interspace Material
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made of plastic, aluminum, carbon fiber or other radiolucent. Interspace material will have a low atomic Z number.
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State purpose of grid Aluminum covering.
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to provide structure and protection
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Describe disadvantage of using grids
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Requires higher mAs exposure factors, which increases patient dose, Requires more precise positioning skills
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Describe advantage of using grids
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* Improves image quality by reducing the amount of scattered xrays reaching the IR
* Grids help "clean up" scattered radiation |
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List types of grids
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Linear Focused
Linear Non-focused or parallel Cross hatch * linear focused is the most common |
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Linear Non-focused or Parallel Grid
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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 |
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Linear Focused Grid
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*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. |
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Parallel Non-focused grids best used with what type of SID?
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Longer SID
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List factors that increase scatter radiation
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increases in patient thickness, larger field sizes, decreases in atomic number of tissue
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First Grid
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1913
American! radiologist Gustav Bucky (crosshatch) |
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Improved Grid
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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. |
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Grid Ratio
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defined as ratio of height of the lead strips to the distance between the strips GR = h/D
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Grid Ratio
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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
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Grid Ratio
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H/D , inverse relationship between distance between lead strips and grid ratio when height remains the same. > grid ratio < scatter; < grid ratio > scatter
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Grid Frequency or
Strip Density |
the number of grid lines per inch (states on a grid as the LPI (lines per inch)
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Reciprocating Grid
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Bucky & Chest Board: Move during the exposure
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Stationary Grids
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Do not move.. Taped in place on the cassette or IR
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Cross Hatch grid
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* 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 |
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Grid Cutoff
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Undesirable absorption of the useful, image-forming xrays by the grid strips.
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How does grid cut off happen
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By improper alignment of the grid to the central ray
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How does grid cut off effect the image?
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The image will appear underexposed and grid strips are visible.
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List types of grid cutoff
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*Off Near Focus or Off Far focus
*Off Level *Focused Grid Upside Down *Off Center *Angling Against Grid Lines |
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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
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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
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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.
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Off Center
Grid Cut Off |
CR not centered to grid
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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
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Common Grid Ratios
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5:1, 6:1, 8:1, 10:1, 12:1, 16:1
10:1 and 12:1 considered the same |
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Grid Focusing Distance
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recommended SID range for a grid
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Higher Grid Ratio compared to a lower grid ratio
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Heavier, thicker, better clean up, requires more precise positioning of CR to grid. < Positioning latitude
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When should you select a higher grid ratio?
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* When you have a really big patient
* When you use 120 kVp or > * When max cleanup of scattered radition is required |
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When should you select a lower grid ratio?
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When you need > positioning latitute - trauma or portables
When max clean up not so important |
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What type of Grid is usually found in the Bucky?
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* Usually 8:1, 10:1 or 12:1, linear focused
* And it reciprocates |
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Density Maintenance Grid Factors
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5:1 - 2
6:1 - 3 8:1 - 4 10:1 and 12:1 - 5 16:1 - 6 |
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Air Gap Technique
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* An option to grid use on certain exams
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Air Gap Technique
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uses OID instead of a grid to reduce the intensity of scattered radiation reaching the IR
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Air Gap Technique
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By using air gap technique, some of the scattered photons will miss hitting the IR because of the physical distance between patient and IR
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Air Gap Technique
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The increased OID requires a 72" SID to help reduce magnification
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Possible applications of Air Gap Technique today
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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 |
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Bucky or Bucky Tray
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if bucky used, increase OID = magnification of anatomy. Generally 3-4 inch distance between table top and bucky tray
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Grids influence which radiographic properties
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Contrast and Density
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Grids have NO effect on which radiographic property
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Recorded Details
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Most important grid factor
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Grid Ratio
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