Imaging Adler CH 5&6
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| contrast decreased from unwanted exposure | scatter/ fog
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| factors that contribute to increased scatter | KVP, field size, patient thickness
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| density you can see | optical density (OD)
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| optical density caused by ________ &__________ | transmission and compton scatter
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| Collimation ________ area of exposure and _________ contrast | decrease; increase
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| _________improves spatial resolution, contrast resolution,and reduces patient dose. | compression
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| 4 types of beam restrictors | aperture diaphragm, cones and cylindars, variable-aperture diaphragm, and positive beam limiting device (PBL)
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| a flat piece of lead with hole with prescribed SID Simplest form | aperture diaphragm
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| used too produce circular projected field on selected areas to produce better scale of contrast and less exposure | cones and cylindars
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| most common collimator reduces patient dose and improves contrast has longitudinal and lateral blades that move independantly | variable aperture collimator
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| variable aperature collimator blades are how thick? | 3mm thick
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| what is light localization accomplished with? | lamp and mirror
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| PBL | positive Beam Limiting device (automatic collimators)
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| PBL mandated by FDA in what year? Is this still a regulation? | 1974
NO
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| off focus radiation is ___________ focal spot | out side
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| Who invented Grids? In what year? Who revised the design? | Gustave Buckey ; 1913 ; Potter
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| what is a grid purpose? | to reduce scatter to improve contrast
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| Grid ratio equation | height of lead strip/ distance between them
H/D (answer:1)
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| to use a grid you have to have ___ KVP and a thickness of ____ cm | 70 KVP and 10cm
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| the ________ the grid ratio the________ scatter will be absorbed, the _______ patient dose | higher; more; higher
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| the # of grid strips per cm or inch | grid frequency
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| if contrast improves ____to_____ a grid is worth using if below 1.5 its not worth using | 1.5-2.5
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| Grid conversion factors- no grid, 5:1, 6:1, 8:1, 10:1 or 12:1, 16:1 | 1, 2,3,4,5,6
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| Grid ratio formula | mAs1=GCF1
mAs2 GCF2
mAs2
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| Types of grids | parallel, crossed, focused, moving, stationary
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| simplest type of grid lead strips parallel, grid cut off most common | parallel grid
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| result of grid absorbing the primary x-rays | grid cut off
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| 2 parallel grids stack on top of one another, absorb more scatter but have to increase mas cant use angles | crossed grid
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| lead strip coincide with divergence of beam, no grid cut off marked to indicate top | focused grid
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| grid is oscillating or reciprocating during procedure to blur grid lines | moving grid
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| moving grids create _______OID | 3 inches
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| occurs whenthe geid tilts during horizontal beam radiography or sinks into bed, results in grid cut off | off level grid
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| grid cut off on one side | off center grid
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| grid with cut off at edges | off focused grid
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| grid with severe cut off on lateral sides (edges) | upside down grid
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| If you need a grid and dont have one what technique can you use? | air gap technique
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| how much OID can be use in place of a grid? | 10 - 15 cm of OID
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| mAs goes up __% for every cm of OID | 10%
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| invisible image | latent
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| visible image | manafest
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| correctly matching the color sensitivity of the film to the color emission of the intenifying screen | spectral matching
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| layer that holds and forms the latent image composed of silver halide crystals | emulsion layer
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| "glue" layer that binds emulsion to film | adhesive layer
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| gelatin layer that holds crystals in place | supercoat emulsion
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| types of film | emulsion, double emulsion, single emulsion, direct exposure
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| year of Gurney-Mott theory | 1938
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| potential differance and HVL | kilovoltage (KVP)
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