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Grids

Grid Study sheet

QuestionAnswer
Define grid. Device used to improve contrast of the radiographic image.
When is a grid used? Body thickness exceeds 10 cm or kVp is above 60
When did Gustav Bucky invent the grid? 1913
When did Hollis Potter invent the moving grid? 1920
Radiolucent interspace materials are usually made out of what 2 materials? Aluminum and plastic fibers
What is the formula for grid ratio? Grid ratio = h/d (h = height of lead strips, d = interspace width)
Define grid frequency. Number of grid lines per inch or centimeter.
As the lead content of a grid increases, the ability of the grid to remove scatter and improve ____ ______. contrast, increases
Name the 3 grid patterns. Linear, Criss-cross, Rhombic (LCR)
Name the 2 grid types. Parallel (Lead and interspace materials running parallel), and focused (central grid strips parallel and other strips are inclined.)
What is the formula for grid selectivity? Selectivity = % primary radiation transmitted DIVIDED by % scatter radiation transmitted
What symbol identifies selectivity? Greek letter Sigma
What is the formula for Contrast Improvement Factor K? K = Radiographic contrast with the grid DIVIDED by Radiographic contrast without the grid
Define off-level. The tube is angled across the long axis of the strips.
Define off-center. The tube must be centered along the central axis of a focus grid.
Define off-focus. The proper SID is not used.
Define upside down. Occurs if proper distance is not used with the specified distance.
What are the 2 types of grid movement? Reciprocating (back & forth); Oscillating (circular movement)
Define air-gap technique. An alternative to the use of a grid.
When is the air-gap technique used? Magnification radiography
What is the disadvantage to using the air-gap technique? The loss of sharpness that results from increased OID.
What is the Moire effect? Grid error that occurs with digital image receptor systems when grid lines are captured and scanned parallel to the scan lines in the imaging plate readers.
An __________ relationship exists between the distance between lead strips and grid ratio when the height of the grid strips remains the same. Inverse
As the lead content of a grid increases, the ability of the grid to remove scatter and improve contrast ____________. Increases
__________ grids are more commonly used in clinical practice because they can be used when performing procedures requiring tube angulation. Linear
The distance from the face of the grid to the points of convergence of the lead strips is called the ___________ __________. Grid radius
For the grid to be properly focus, the x-ray tube must be located along the _________ __________. Convergence line
______ _______ _________ girds are made for use in mammography. Short focal range
________ _________ ________ are used for chest radiography. Long focal range
Focused grids with ________ _____ ____ allow for greater latitude in alignment of the tube with the grid. Lower grid ratios
Grid conversion factors __________ with higher grid ratios and increasing kVp. Increase
The grid with the higher lead content would have a ___________ selectivity. Greater
Created by: rad1958tech on 2008-11-01



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