Grids
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| show | kVp, field size, patient thickness
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| what are some ways to reduce scatter? | show 🗑
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| Extremely effective in reducing the amount of scatter reaching the IR | show 🗑
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| show | Alternating radiopaque material (lead- grid strips) and radiolucent material (aluminum or plastic - interspace material.
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| show | to maintain a precise separation between the delicate lead strips of the grid.
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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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| show | height of the grid divided by the interspace width
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| show | Grid Ratio= H/D
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| what are the three most important dimensions on a grid? | show 🗑
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| show | density differences
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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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| show | less grid lines
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| show | more dosemore technique
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| what is the range of grid frequencies | show 🗑
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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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| show | lead
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| What is the principle function of grids? | show 🗑
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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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| what is the formula for the contrast improvement factor (k)? | show 🗑
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| show | 1.5-2.5 (radiographic contrast is doubled when grids are used; a k of 1 indicates no improvement)
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| Is the k higher for higher ratio grids? | show 🗑
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| show | Bucky factor
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| show | incident remnan radiation/ transmitted image - forming radiation = patient dose with grid/ patient dose without grid
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| The higher the grid ratio the ________the bucky factor. | show 🗑
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| A increase in ________ will _______ the bucky factor. | show 🗑
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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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| Parallel (linear) grid | show 🗑
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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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| Lead grid strips running parallel to both the long and short axes of the grid | show 🗑
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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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| show | They coincide with the divergence of the beam.
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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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| show | They are images made when primary x rays are absorbed in the grid strips.
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| Moving grids | show 🗑
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| show | Potter-bucky diaphragm (named after Hollis E. Potter who developed this idea in 1920)
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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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| Oscillating grids | show 🗑
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| Reciprocating grids | show 🗑
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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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| show | caused by angle of tube or central ray; cuts across or perpendicular to grid lines; cutoffon entire image; most common
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| show | cutoff on one side than the other due to central ray not centered on grid
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| show | not using with proper SID; only occurs with focused grids; cutoff on periphery but not at severe as focused grid upside down (use a parallel grid if have no control over SID)
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| show | least common;a radiographic image is taken with an upside down focused grid shows sever grid cutoff on either side of the central ray
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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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| show | IR is moved 10-15 cm from pt. Portion of x rays are scattered away from IR contrast (mAs is increased approx. 10% for every cm of air gap)
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| what are some disadvantages of the air gap technique? | show 🗑
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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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| For diagnostic kVp range the highest quantity is at ______ to patient. (backscatter) | show 🗑
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| show | 90 degrees
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| show | 50%; 90%
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| When do we use a grid? | show 🗑
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| show | It is a zebra pattern that shows when you use tooo low a frequency grid with electronic imaging or a grid is put into a bucky
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| what is grid cutoff? | show 🗑
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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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