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Imaging Adler CH 5&6

QuestionAnswer
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)
Created by: 100001051240277