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Imaging Adler CH 5&6
| Question | Answer |
|---|---|
| contrast decreased from unwanted exposure | scatter/ fog |
| factors that contribute to increased scatter | KVP, field size, patient thickness |
| density you can see | optical density (OD) |
| optical density caused by ________ &__________ | transmission and compton scatter |
| Collimation ________ area of exposure and _________ contrast | decrease; increase |
| _________improves spatial resolution, contrast resolution,and reduces patient dose. | compression |
| 4 types of beam restrictors | aperture diaphragm, cones and cylindars, variable-aperture diaphragm, and positive beam limiting device (PBL) |
| a flat piece of lead with hole with prescribed SID Simplest form | aperture diaphragm |
| used too produce circular projected field on selected areas to produce better scale of contrast and less exposure | cones and cylindars |
| most common collimator reduces patient dose and improves contrast has longitudinal and lateral blades that move independantly | variable aperture collimator |
| variable aperature collimator blades are how thick? | 3mm thick |
| what is light localization accomplished with? | lamp and mirror |
| PBL | positive Beam Limiting device (automatic collimators) |
| PBL mandated by FDA in what year? Is this still a regulation? | 1974 NO |
| off focus radiation is ___________ focal spot | out side |
| Who invented Grids? In what year? Who revised the design? | Gustave Buckey ; 1913 ; Potter |
| what is a grid purpose? | to reduce scatter to improve contrast |
| Grid ratio equation | height of lead strip/ distance between them H/D (answer:1) |
| to use a grid you have to have ___ KVP and a thickness of ____ cm | 70 KVP and 10cm |
| the ________ the grid ratio the________ scatter will be absorbed, the _______ patient dose | higher; more; higher |
| the # of grid strips per cm or inch | grid frequency |
| if contrast improves ____to_____ a grid is worth using if below 1.5 its not worth using | 1.5-2.5 |
| Grid conversion factors- no grid, 5:1, 6:1, 8:1, 10:1 or 12:1, 16:1 | 1, 2,3,4,5,6 |
| Grid ratio formula | mAs1=GCF1 mAs2 GCF2 mAs2 |
| Types of grids | parallel, crossed, focused, moving, stationary |
| simplest type of grid lead strips parallel, grid cut off most common | parallel grid |
| result of grid absorbing the primary x-rays | grid cut off |
| 2 parallel grids stack on top of one another, absorb more scatter but have to increase mas cant use angles | crossed grid |
| lead strip coincide with divergence of beam, no grid cut off marked to indicate top | focused grid |
| grid is oscillating or reciprocating during procedure to blur grid lines | moving grid |
| moving grids create _______OID | 3 inches |
| occurs whenthe geid tilts during horizontal beam radiography or sinks into bed, results in grid cut off | off level grid |
| grid cut off on one side | off center grid |
| grid with cut off at edges | off focused grid |
| grid with severe cut off on lateral sides (edges) | upside down grid |
| If you need a grid and dont have one what technique can you use? | air gap technique |
| how much OID can be use in place of a grid? | 10 - 15 cm of OID |
| mAs goes up __% for every cm of OID | 10% |
| invisible image | latent |
| visible image | manafest |
| correctly matching the color sensitivity of the film to the color emission of the intenifying screen | spectral matching |
| layer that holds and forms the latent image composed of silver halide crystals | emulsion layer |
| "glue" layer that binds emulsion to film | adhesive layer |
| gelatin layer that holds crystals in place | supercoat emulsion |
| types of film | emulsion, double emulsion, single emulsion, direct exposure |
| year of Gurney-Mott theory | 1938 |
| potential differance and HVL | kilovoltage (KVP) |
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100001051240277
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