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The Grid
Principles of Radiographic Imaging 5th Edition Chapter 18
| Question | Answer |
|---|---|
| Two Linear grids placed on top of one another so that the lead strips form a criss-cross pattern | Criss-Cross Grid |
| Two linear grids placed on top of one another so that the lead strips form a criss-cross pattern | Cross-Hatched Grid |
| A grid created with the central grid strips parallel with the strips and becoming more inclined as they move away from the central axis; the lines would intersect along a point in space called the line of convergence | Focused Grid |
| A device used to improve contrast of the radiographic image | Grid |
| The result of the primary beam being angled into the lead strips | Grid Cutoff |
| The number of grid lines per inch or centimeter | Grid Frequency |
| The ratio of the height of the lead strips to the distance between the strips | Grid Ratio |
| A grid with lead strips running in only one direction | Linear Grid |
| A grid created with the lead and interspace strips running parallel to one another; the lines will never intersect | Parellel Grid |
| Why does a grid improve contrast? | Grids absorb scattered radiation before it can reach the image receptor |
| As a general rule, when should a grid be used? | Body part thickness exceeds 10 cm, and kVp is above 60 |
| How is a grid constructed? | Selection of materials, grid ratio, and grid frequency |
| Define Grid Ratio: | The ratio of the height of the lead strips to the distance between the strips |
| What type of grid pattern has lead strips running in only one direction? | Linear Grid |
| How is a focused grid designed? | The central grid strips are parallel and as the strips move away from the central axis they become more and more inclinded |
| As the ability of a grid to clean up scatter increases, what is the effect on patient dose and image receptor exposure? | The more efficient a grid is at absorbing scatter, the less image receptor exposure. To compensate for the loss of exposure there is an increase in mAs, which increases patient dose. |
| How is the contrast improvement of a grid measured? | The contrast improvement factor. K=radiographic contrast with the grid, over radiographi. The higher the K factor, the greater the contrast. |
| How does an off-level grid error occur? | When the tube is angled across the long axis of the grid strips |
| How does the air-gap technique improve contrast? | The technique involves placing the patient at a greater object IR eistance, that creating an air grap between the patient and IR |
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Dallas1856
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