Grid Flashcards
Why are Grids needed?
- As the ___ interacts with the patient’s ___, ___ radiation is created.
- Remember ___ Interaction!
- ___ radiation has ___ energy level than the primary beam so it will produce a “___” on the x-ray film.
- Fog = unwanted ___ on the radiographic image. This will make the film look ___.
Why are Grids needed?
- As the primary beam interacts with the patient’s tissue, scatter radiation is created.
- Remember Compton Interaction!
- Scatter radiation has lower energy level than the primary beam so it will produce a “fog” on the x-ray film.
- Fog = unwanted density on the radiographic image. This will make the film look gray.
Gustav Bucky
- Inventor of the ___– 1913
- Function is to: “___” or “clean up” the ___ before reaching the ___.
Gustav Bucky
- Inventor of the grid– 1913
- Function is to: “stop” or “clean up” the scatter radiation before reaching the IR.
Purpose of the Grid
- Improves radiographic ___ (or gray scale- eliminates ugly gray) in the image by:
- ____ scattered radiation before it reaches the image receptor
NOTE: Does not save ___ to patient!
Purpose of the Grid
- Improves radiographic contrast (or gray scale- eliminates ugly gray) in the image by:
- Absorbs scattered radiation before it reaches the image receptor
NOTE: Does not save radiation dosage to patient!
Where are grids placed?
Grids are placed between the ___ and the ___
- When to use a grid:
- If the body part is over ___ and if ___ kVp or higher
Where are grids placed?
Grids are placed between the patient and the IR
- When to use a grid:
- If the body part is over 10 cm and if > 60 kVp or higher
Basic Grid Construction
- ___ lead strips (can see on film) - lead strips will stop the ___
- • Separated by ___ (can’t see on film)interspace material
– Typically ___ or ___
- ___ pass through the interspace
Basic Grid Construction
- Radiopaque lead strips (can see on film) - lead strips will stop the scatter radiation
- • Separated by radiolucent (can’t see on film) interspace material
– Typically aluminum or plastic
-Primary beam pass through the interspace
Grid Dimensions
• 1.) GRID RATIO
• h = the ___ of the ___ strips
• D = the ___ between the strips
- the ___ of the interspace material
• ___ or ___ material
Grid Dimensions
• 1.) GRID RATIO
• h = the height of the radiopaque strips
• D = the distance between the strips
- the thickness of the interspace material
• Aluminum or plastic material
Grid Ratio
- ___ of lead strips divided by ___ between the lead strips
– Grid ratio = __/__
Grid Ratio
- Height of lead strips divided by distance between the lead strips
– Grid ratio = h/D
Grid Ratio Example
- If a grid has an interspace of 0.5mm, the thickness of the lead strips is .025mm and lead strips that are 3mm high, what is it’s grid ratio?
● GR = __mm/__mm
● GR = __:__
Grid Ratio Example
- If a grid has an interspace of 0.5mm, the thickness of the lead strips is .025mm and lead strips that are 3mm high, what is it’s grid ratio?
● GR = 3mm/0.5mm
● GR = 6:1
Why is Grid Ratio important?
- Higher grid ratio = More ___ in ___
- Typical grid ratio range is ___ to ___
higher ratios usually used with bariatric patients - lower ratios are usually used for extremities due to less body thickness
Why is Grid Ratio important?
- Higher grid ratio = More efficient in removing scatter
- Typical grid ratio range is 5:1 to 16:1
higher ratios usually used with bariatric patients - lower ratios are usually used for extremities due to less body thickness
2.) Grid Frequency
- The number of lead strips per ___ or ___
● Frequency range
– ___-___ lines/in
– ___-___ lines/cm
Most Common: ___-___ lines/inch
● Typically higher frequency grids have ___ lead strips
Benefits: adding more lead removes more scatter
2.) Grid Frequency
- The number of lead strips per inch or cm
● Frequency range
– 60-200 lines/in
– 25-80 lines/cm
Most Common: 85-103 lines/inch
● Typically higher frequency grids have thinner lead strips
Benefits: adding more lead removes more scatter
Digital Imaging Systems
● Very high-frequency grids
– ___ lines/in
- ___ lines/cm
● Recommended for use with ___ systems
- Minimizes ___ appearance
Digital Imaging Systems
● Very high-frequency grids
– 103-200 lines/in
- 41-80 lines/cm
● Recommended for use with digital systems
- Minimizes grid line appearance
In General…
● Lead content is greater in a grid with a ___ ratio and ___ frequency
● As ___ content increases, ___ increases and therefore ___ increases
In General…
● Lead content is greater in a grid with a high ratio and low frequency
● As lead content increases, removal of scatter increases and therefore contrast increases
Disadvantages of using a Grid
● ___ radiation dose to the patient when changing from screen cassette (___):
–Higher ratio = ___ (more lead)
higher ___ to the patient
Disadvantages of using a Grid
● Higher radiation dose to the patient when changing from screen cassette (tabletop):
–Higher ratio = more radiation (more lead)
higher radiation dose to the patient
Rule of Thumb:
- Non-Grid to Grid
–___ mAs by ___
3 mAs at 55 kVp for finger non-grid but changing to Grid
___ x/ ___ = ___ mAs
● Grid to Non-Grid
–___mAs by ___
160 mAs at 70 kVp for KUB using a Grid but change to non- grid
___ x/ ___ = ___ mAs for Non-Grid
Rule of Thumb:
- Non-Grid to Grid
–multiply mAs by 4
3 mAs at 55 kVp for finger non-grid but changing to Grid
3 x 4 = 12 mAs
● Grid to Non-Grid
–Divide mAs by 4
160 mAs at 70 kVp for KUB using a Grid but change to non- grid
160/4 = 40 mAs for Non-Grid
Potter-Bucky Diaphragm
- Dr. ____ made improvements to the use of grids
- Realigned lead strips to ___
- ___ grid during ___ to make lines ___ on image
Potter-Bucky Diaphragm
- Dr. Hollis Potter made improvements to the use of grids
- Realigned lead strips to run in one direction
- Moved grid during exposure to make lines invisible on image
Stationary Grid Vs. Moving Grid
- Examples of a moving grid:
1. ___ Grid – a ___-driven grid which moves the grid “___ motion” during the exposure. (Advantage: didn’t allow human eye to see lead lines on image)
2. ___ Grid – a ___-like device in the ___ of the bucky tray. A strong ___ pulls the grid in a ___ fashion around the grid frame.
Stationary Grid Vs. Moving Grid
- Examples of a moving grid:
1. Reciprocating Grid – a motor-driven grid which moves the grid “back and forth motion” during the exposure. (Advantage: didn’t allow human eye to see lead lines on image)
2. Oscillating Grid – a spring-like device in the corners of the bucky tray. A strong electromagnet pulls the grid in a circular fashion around the grid frame.
Grid Patterns
● ___ or ___ (Dr. ___)
● ___Grid
● ___(Parallel or Focused)
Grid Patterns
● Criss-cross or cross-hatched (Dr. Bucky)
● Rhombic Grid
● Linear (Parallel or Focused)
Criss-Cross or Cross-Hatched
● Two linear grids ___ at ___ to each other.
● Advantage: Best ___
● Disadvantage:
- ___ must be centered ___ to ___ at all times (no ___)
- Grid must remain ___
- ___ to the patient
Linear grid and cross-hatch= best cleanup
Criss-Cross or Cross-Hatched
● Two linear grids superimposed at right angles to each other.
● Advantage: Best grid clean up
● Disadvantage:
- CR must be centered perpendicular to grid at all times (no CR angulation)
- Grid must remain flat
- Higher radiation dose to the patient
Linear grid and cross-hatch= best cleanup
Rhombic Grid:
● Lead strips are placed ___ degrees to each other. (___ shape)
● Allowed for ___ the ___ in ___
– But only ___ degree angles
Rhombic Grid:
● Lead strips are placed 45 degrees to each other. (diamond shape)
● Allowed for angling the tube in any direction
– But only 5 degree angles
Linear Grid
● Lead strips run the ___ of ___
● ___ angle CR ___ the lead strips
● Allows ___ to be ___ along the ___ of grid without obtaining “___”
Linear Grid
● Lead strips run the length of cassette
● Can not angle CR against the lead strips
● Allows primary beam to be angled along the long axis of grid without obtaining “cut-off”
Two types of linear grids
- ___ - Lead strips are ___ to each other (grids can be used at longer SID, 72” before grid cutoff)
- ___ - Lead strips match the ___ ////||||\\ (everything points to the center of the grid, ex 40”)
Two types of linear grids
- Parallel - Lead strips are || to each other (grids can be used at longer SID, 72” before grid cutoff)
- Focused - Lead strips match the divergence of beam ////||||\\ (everything points to the center of the grid, ex 40” )
Parallel Linear Grids
● All lead strips are ___
● Absorb ___ of primary beam
– Resulting in ___
● Best used at ___
Parallel Linear Grids
● All lead strips are parallel to one another
● Absorb a large amount of primary beam
– Resulting in some cut-off
● Best used at long SID
Parallel Grid:
● Cons:
– Can not be used at ___
– WHY???
Parallel Grid:
● Cons:
– Can not be used at short SID
– WHY???
because parallel grid doesn’t match the divergent line in CR
Focused Linear Grids
- Lead strips are angled to ___
- ___ lead strips ___ the center of the grid
- Canting of the grid /////////||||||||\\\\\\
- Convergence Line= ___ from the ___ of the grid to the ___ of the lead strips ___ the grid.
Focused Linear Grids
- Lead strips are angled to match divergence of beam
- Outside lead strips tilt toward the center of the grid
- Canting of the grid /////////||||||||\\\\\\
- Convergence Line= distance from the face of the grid to the point of convergence of the lead strips above the grid.
Focused Linear Grids
___ or ___: distance that which to use the grid.
- ___ positioning latitude
- ___results in peripheral cut-off at the sides of the image
- Only useful at ___
- Higher ratio grids require ___
● Cons:
– More ___ to purchase
–Must be careful to use ___ at the correct ___
Focused Linear Grids
Grid Radius or Focal Range: distance that which to use the grid.
- Narrow positioning latitude
- Improper centering results in peripheral cut-off at the sides of the image
- Only useful at preset SID distance
- Higher ratio grids require careful alignment with tube
● Cons:
– More expensive to purchase
–Must be careful to use grid at the correct SID
Grid Latitude:
● “room” or ___ of ___ when using a grid
- Grid Radius was 45-72” SID … You place the grid at 43” SID.
Was you image good? Depends of the grid’s ____. With a ___ ratio, ___. With a ___ ratio, not as good.
Grid Latitude:
● “room” or margin of error when using a grid
- Grid Radius was 45-72” SID … You place the grid at 43” SID.
Was you image good? Depends of the grid’s latitude. With a high ratio, good. With a low ratio, not as good.
Grid Cut Off
- “Unwanted ___ of the primary beam.”
- Occurs when the ___ of the grid are ___ the ___.
- Will cause the image to be ___.
Grid Cut Off
- “Unwanted attenuation of the primary beam.”
- Occurs when the lead lines of the grid are absorbing the primary beam.
- Will cause the image to be too light.
Common Causes of Grid Cut Off:
● Angle… (detent)
● Lateral… (lines of grid no longer matching primary beam)
● Angle… (lopsided IR)
● Wrong…
● Using… (focus grid)
● Moire… (digital systems)
Common Causes of Grid Cut Off:
● Angle CR against the grid lines (detent)
● Lateral decentering of the grid (lines of grid no longer matching primary beam)
● Angle grid against the CR (lopsided IR)
● Wrong distance with either parallel or focus grids
● Using the grid upside down (focus grid)
● Moire effect (digital systems)
Off Center Grid: Lateral decentering
● Common problem with ___
● You must make sure the ___ matches the ___ of the grid ___.
● Density will appear ___ to ___ on the image.
–“center to the ___”
Off Center Grid: Lateral decentering
● Common problem with focus grids.
● You must make sure the divergence beam matches the canting of the grid strips.
● Density will appear dark to light on the image.
–“center to the bucky tray”
Off-level Grid
● Common on ___.
● Grid not the ___ (not level) or ___ to the CR.
● Density will appear ___ to ___ on the ___ of the image.
Off-level Grid
● Common on portables.
● Grid not the same plane (not level) or perpendicular to the CR.
● Density will appear dark to light on the edges (sides) of the image.
Off-focus grid:
● Grid used ___ of the ___ SID range.
● Density will appear ___ on ___ of the image but correct density ___ of the image.
● What about a parallel grid used at a short SID? ___ in middle, ___ light
Off-focus grid:
● Grid used outside of the intended SID range.
● Density will appear lighter on each side of the image but correct density in the center of the image.
● What about a parallel grid used at a short SID? Dark in middle, both sides light
Upside down Grid-
● Focus grid – lead strips are now ___ the ___ of the primary beam.
● Density will be ___ in the middle of the image but ___ on the sides.
● ___ change when comparing to using a ___ outside of the ___.
Upside down Grid-
● Focus grid – lead strips are now opposing the divergence of the primary beam.
● Density will be okay in the middle of the image but light on the sides.
● More abrupt change when comparing to using a focus grid outside of the focus range.
Moire Effect
● ___ systems
–When grid lines are ___to ___lines
● ___ grids can prevent this phenomenon
Moire Effect
● Digital systems
–When grid lines are parallel to scan lines
● High frequency grids can prevent this phenomenon
Grid lines can appear if:
● Pressure…
● Improper…
● Using…
● Grid was…
Grid lines can appear if:
● Pressure on the grid
● Improper centering of x-ray tube to grid
● Using a grid outside of the focal range
● Grid was not moving during the exposure
Air Gap Grid:
● An ___ to the use of a grid.
● Method reduces ___ reaching the ___.
● Place the patient (part) ___cm or ___ away from the film. (___ OID = ___ grid )
● Scatter radiation leaving the patient’s body as a ___ of energy will interact with ___ in the ___.
● This technique will improve ___….BUT –
___ of the patient is created!
Decreases ___ of the image
Air Gap Grid:
● An alternative to the use of a grid.
● Method reduces scatter radiation reaching the IR.
● Place the patient (part) 10-15 cm or 4-6” away from the film. (10” OID = 15:1 grid )
● Scatter radiation leaving the patient’s body as a low level of energy will interact with particles in the air.
● This technique will improve contrast….BUT –
Magnification of the patient is created!
Decreases recorded detail of the image
