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24 Cards in this Set
- Front
- Back
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density (in terms of image quality)
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overall darkness of image
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latitude
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ability to display many different gray scales in density for various portions of the anatomy imaged or the size of the range in radiation levels transmitted through the body that appear as shades of gray
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noise
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random variation in the background darkness
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what isthe opposite of latitude
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contrast
if contrast increases, latitude decreases |
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what comprises image contrast
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combined effects of subject contrast and image receptor contrast
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what is subject contrast
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difference in teh # of XR that pass through various parts of the body and impinge on film or digital receptor
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what does subject contrast depend on
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thickness differences in anatomic structures
density differences in anatomic structures differences in Z introduction of contrast media kVp, filtration effect of grids |
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what affects image receptor contrast for a film screen system
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selection of film and its characteristic curves
film processing conditions light and background fog of the film density of the film |
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what affects film fog
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improper film storage
film processing conditions (ie high temps) light leaks |
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how does film fog affect contrast
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it doesnt'
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image receptor contrast in CR/DR system depends on what
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window and level setting for display
software processing of data display monitor contrast gradient |
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unsharpness or blur depends on what
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focal spot
motion intesnifying screen unsharpness or thickness of screens affecting light dispersion absorption unsharpness of anatomic organs parallax from dual emulsion film wiht opposite sides displaced |
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why does focal spot blur occur
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focal spot has a dimension and b/c magnification of the image occurs b/c of divergence of XR and the displacement of anatomy away from receptor
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how is blur affected by focal spot size and magnification
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increased focal spot size and greater magnification increases blur
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different ways to measure spatial resolution
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lp/mm
best MTF graph |
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wide LSF
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line spread fxn
wide LSF significant blur and degraded spatial resolution |
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how to calculate HVL when a linear attenuation coefficient is given
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HVL = 0.693/µ (µ = given linear attenuation coefficient)
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if the linear attenuation coefficient is 0.0693, what is the HVL
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0.693/0.0693 = 10
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if the HVL is 10, what is µ
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10 = 0.693 ÷ x
x = 00693 |
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most common digital XR detector used
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CsI
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most common imaging use for amorphous selenium
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mammo digital detectors
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axes on MTF curves
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vertical = MTF value (fraction of image contrast that is preserved), ranges from 0-1
horizontal = spatial frequency (lp/mm) |
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what does MTF = 1 mean?
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1 = image system doesn't degrade the contrast at all
0 = all the contrast is blurred to 0 by the imaging system; if there is no noise, a reduction in MTF of an object with 100% contrast is the limiting spatial resolution of hte image receptor |
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where are large objects and small objects on MTF curve
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on horizontal axis: large object is at low frequency (right), small objects are to the left
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