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Grids
Grid Study sheet
| Question | Answer |
|---|---|
| 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
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