Grids
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show | kVp, field size, patient thickness
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show | grid, beam restricting devices
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show | grid
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Grids are made of ________. | show 🗑
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what is the purpose of the interspace material? | show 🗑
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What is the purpose of the grid strips? | show 🗑
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show | Grid casing
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Grids are designed to transmit x rays whose direction is a ________ _____ from source to IR. | show 🗑
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show | 80-90% of scatter
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Grid Ratio | show 🗑
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show | Grid Ratio= H/D
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show | T = the thickness of the grid stripD= the width of the interspace materialH = the height of the grid
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what is contrast? | show 🗑
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show | False - Higher ratio grids are better at cleaning up scatter due to the angle of deviation being smaller
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show | more dose
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show | Grid Frequency
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If a grid has a high frequency will it show more or less grid lines? | show 🗑
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show | more dosemore technique
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show | 25-45 lines per centimeter (60-110 lines per inch)
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What is the formula for grid frequency? | show 🗑
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show | To maintain a precise separation between the delicate lead strips of the grid.
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show | aluminum or plastic
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What material is mostly used for the grid strips? | show 🗑
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show | To improve image contrast
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Name 3 factors that affect grid performance. | show 🗑
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What is the contrast improvement factor? | show 🗑
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show | k= radiographic contrast with grid / radiographic contrast without a grid
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what is the k range? | show 🗑
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Is the k higher for higher ratio grids? | show 🗑
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Increase of technique to produce the same optical density. Attempt to measure the penetration of both primary and scatter radiation through the grid. | show 🗑
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what is the formula for Bucky factor? | show 🗑
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show | higher
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show | kVp, increase
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With an increase with bucky factor what will hapen to patient dose? | show 🗑
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Ratio of transmitted primary radiation and transmitted scatter radiation. | show 🗑
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show | Greek sigma = primary radiation transmitted through grid/ scatter radiation tansmitted through grid
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show | higher, scatter
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show | Parallel (linear), Crossed, Focused, Moving
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show | simplest; all lead grid strips are parallel; clean up scatter radiation in only one direction
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Undesirable absorption of primary x rays by the grid. | show 🗑
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With Linear grids if you do not use the proper ______ you will get grid cutoff. | show 🗑
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show | Crossed grid
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show | Must position correctly so the x ray beam coincides with the center of the grid and if table and tube are not aligned properly you will get grid cutoff
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show | Focused grids
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How do the focused grid lead strips lie? | show 🗑
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show | False - all focused grids are marked with intended focal distance. It must be used at the specified SID.
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What are grid lines? | show 🗑
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Moving grids | show 🗑
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What is another name for the moving grids? | show 🗑
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_______________ are usually used as moving grids. | show 🗑
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What are the two types of moving grids? | show 🗑
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show | positioned in a frame , a powerful electromagnet pulls the grid to one side and releases it at the beginning of the exposure, and oscillates in a circular fashion
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show | moving grid that is motor driven back and forth several times during exposure
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show | - requires a bulky mechanism - distance between patient and IR is increased due to mechanisms increase in magnification and image blur-exposure time is longer
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What are four types of problems that can occur with focused grids? | show 🗑
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Off-level grid | show 🗑
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show | cutoff on one side than the other due to central ray not centered on grid
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off-focused grid | show 🗑
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Upside down grid | show 🗑
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What are some common grid ratios used? | show 🗑
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What are some disadvantages to using a grid? | show 🗑
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What technique can we use in place of grids? | show 🗑
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What is the air gap technique? | show 🗑
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show | increased dose for pt. and image magnification with associated focal spot blur
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show | No, it does not act as a filter. The scattered x rays diverge from the IR due to the distance between the patient and IR.
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show | 180 degrees
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show | 90 degrees
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In the chest, what percentage of the useful density is due to scatter? Abdoment? | show 🗑
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show | when the part is greater than 10-12 cm thick and the kVp is greater than 60
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What is the moire effect? | show 🗑
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show | undesirable absorption of primary x rays by the grid
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show | lead lines lie on the imaginary radial lines of a circle centered at the focal spot so they coincide with divergence of x ray beam
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