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Grids

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Question
Answer
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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