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| what is the 15% rule |
increase kVp by 15% divide mAs by 2
decrease kVp by 15% multiply mAs by 2 |
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usnavalmd Wed, 18 Feb 2009 22:27:23 GMT |
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| what is photographic effect used for |
to figure out which technique has the greatest or least density |
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usnavalmd Wed, 18 Feb 2009 22:27:23 GMT |
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| what is the formula for magnification |
MF= SID/OID |
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usnavalmd Wed, 18 Feb 2009 22:24:22 GMT |
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| what is the formula for photographic effect |
PE = mA x time x kVp2 / distance2 |
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usnavalmd Wed, 18 Feb 2009 22:24:22 GMT |
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| use of beam restriction devices will do what to contrast |
increase |
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usnavalmd Wed, 18 Feb 2009 22:24:22 GMT |
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| increased mAs = __________ contrast |
decreased |
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usnavalmd Wed, 18 Feb 2009 22:24:22 GMT |
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| increased grid ratio =_________ contrast |
increased |
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usnavalmd Wed, 18 Feb 2009 22:20:17 GMT |
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| what are the two major characteristics of image that directly influence the diagnostic quality of the radiograph |
density
contrast |
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usnavalmd Wed, 18 Feb 2009 22:20:17 GMT |
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| the difference in optical density on a radiograph |
radiographic contrast |
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usnavalmd Wed, 18 Feb 2009 22:20:17 GMT |
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| the amount of black metallic silver deposited per unit area during development |
radiographic density |
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usnavalmd Wed, 18 Feb 2009 22:20:17 GMT |
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| what are the anatomical structures ranging from greatest to least mass density |
dental enamel
bone
tissues of water density
fat
gases |
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usnavalmd Wed, 18 Feb 2009 22:13:56 GMT |
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| what is the controlling factor in contrast |
kV |
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usnavalmd Wed, 18 Feb 2009 22:13:56 GMT |
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| the apparent displacement of an object when viewed from different vantage points |
parallax |
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usnavalmd Wed, 18 Feb 2009 22:13:56 GMT |
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| what are the grid conversion factors relative to mAs |
no grid = 1 x mAs
5:1 = 2 x mAs
6:1 = 3 x mAs
8:1 = 4 x mAs
10:1 = 5 x mAs
12:1 = 5 x mAs |
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usnavalmd Mon, 16 Feb 2009 15:29:21 GMT |
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| what are the three factors for understanding grid selection |
1. patient dose increases with increasing grid ratio
2. high ratio grids are usually employed fro high examinations
3. patient dose at high kVp is less than that of low kVp |
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usnavalmd Mon, 16 Feb 2009 15:29:21 GMT |
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| what is the formula for determining contrast improvement of a grid |
k= radiographic contrast w/ the grid /
radiographic contrast w/out the grid |
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usnavalmd Mon, 16 Feb 2009 15:09:59 GMT |
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| what is the formula for determining selectivity of a grid |
selectivity=
% primary radiation transmitted /
% scatter radiation transmitted |
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usnavalmd Mon, 16 Feb 2009 15:09:59 GMT |
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| what are the two functional factors of efficiency of radiographic grids |
selectivity
contrast improvement factor |
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usnavalmd Mon, 16 Feb 2009 15:09:59 GMT |
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| what happens to the grid frequency when the lead strips are thin |
the frequency goes up |
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usnavalmd Mon, 16 Feb 2009 15:09:59 GMT |
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| what is the frequency range for grids |
20-40 lines per centimeter
50-100 lines per inch |
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usnavalmd Mon, 16 Feb 2009 14:49:47 GMT |
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| what are the two benefits of a higher grid ratio |
better cleanup of scatter radiation
increased radiographic contrast and improved detail |
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usnavalmd Mon, 16 Feb 2009 14:49:47 GMT |
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| what is the formula for figuring grid ratio |
r=h/D
grid ratio=height of lead strips/width of spaces between the strips |
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usnavalmd Mon, 16 Feb 2009 14:49:47 GMT |
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| what are the two physical factors that effect the efficiency of radiographic grids |
grid ratio
grid frequency |
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usnavalmd Mon, 16 Feb 2009 14:49:47 GMT |
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| what are the three critical factors when working with a focused grid |
1. center to the grid
2. the proper side of the grid against the film
3. SID |
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usnavalmd Mon, 16 Feb 2009 14:44:12 GMT |
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| with what type of grid is centering and distance not critical |
parallel grid |
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usnavalmd Mon, 16 Feb 2009 14:44:12 GMT |
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| what are the general functions of a radiographic grid |
removal of scatter radiation
designed to transmit only those xrays whose direction is on a line from the source to the image receptor
increase contrast |
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usnavalmd Mon, 16 Feb 2009 14:44:12 GMT |
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| the height divided by the inter space thickness |
grid ratio |
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usnavalmd Mon, 16 Feb 2009 14:44:12 GMT |
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| the number of grid strips or grid lines per inch or per centimeter |
grid frequency |
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usnavalmd Mon, 16 Feb 2009 14:38:26 GMT |
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| the increased absorption of primary radiation in the lead strips resulting from an incorrect SID, improper alignment or centering of the beam to the grid |
grid cutoff |
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usnavalmd Mon, 16 Feb 2009 14:38:26 GMT |
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| if an object is placed lateral to the center of the xray beam what two results may occur |
magnified (elongated)
foreshortened |
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usnavalmd Mon, 16 Feb 2009 14:38:26 GMT |
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| what are the two factors that effect magnification |
SID & OID |
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usnavalmd Mon, 16 Feb 2009 14:38:26 GMT |
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| what are the two factors that determines distortion on a radiograph |
size (magnification)
shape |
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usnavalmd Mon, 16 Feb 2009 14:30:58 GMT |
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| the amount of reduction in image size |
foreshortened |
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usnavalmd Mon, 16 Feb 2009 14:30:58 GMT |
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| unequal magnification of different portions of the same object |
distortion |
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usnavalmd Mon, 16 Feb 2009 14:30:58 GMT |
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| what are the factors that effect subject contrast |
kV
effective atomic number of the body part
patient thickness
tissue mass density
object shape |
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usnavalmd Mon, 16 Feb 2009 14:30:58 GMT |
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| radiographic contrast is designated as what |
long scale ( low contrast )
short scale ( high contrast ) |
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usnavalmd Mon, 16 Feb 2009 14:25:38 GMT |
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| the difference in optical density on a radiograph |
contrast |
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usnavalmd Mon, 16 Feb 2009 14:24:46 GMT |
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| structures that absorb xrays |
radiopaque |
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usnavalmd Mon, 16 Feb 2009 14:24:46 GMT |
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| structures that attentuate (stop) xrays to a relatively small degree |
radiolucent |
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usnavalmd Mon, 16 Feb 2009 14:24:46 GMT |
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| an undesirable fluctuation in optical density of the image |
radiographic noise |
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usnavalmd Mon, 16 Feb 2009 14:15:12 GMT |
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| what body structure has the greatest density |
dental enamel |
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usnavalmd Mon, 16 Feb 2009 14:15:12 GMT |
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| what are the two formulas dealing with distance in radiography |
inverse square law - stating the intensity or exposure rate of radiation at a given distance from a point source is inversely proportional to the square of the distance
direct square law- used to find mA when distance is changed |
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usnavalmd Mon, 16 Feb 2009 14:15:12 GMT |
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| what happens to the radiographic exposure rate as SID increases |
exposure rate decreases |
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usnavalmd Mon, 16 Feb 2009 14:03:14 GMT |
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| what determines only exposure rate and has nothing to do with the penetrating power of the beam |
mA |
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usnavalmd Mon, 16 Feb 2009 14:03:14 GMT |
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| what does doubling mA do to exposure rate |
doubles radiographic exposure rate |
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usnavalmd Mon, 16 Feb 2009 14:03:14 GMT |
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| xray output (R/min) is proportional to what |
mA |
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usnavalmd Mon, 16 Feb 2009 14:03:14 GMT |
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| an increase of kV by 15% does what |
doubles the exposure |
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usnavalmd Mon, 16 Feb 2009 13:58:44 GMT |
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| increase in kV equals what |
increase of remnant radiation reaching the intensifying screen |
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usnavalmd Mon, 16 Feb 2009 13:58:44 GMT |
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| what are the five factors that govern radiation exposure and resulting density |
kVp
mA
time
SID
radiographic object |
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usnavalmd Mon, 16 Feb 2009 13:58:44 GMT |
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| what is an extremely important factor in radiation quality |
density |
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usnavalmd Mon, 16 Feb 2009 13:58:44 GMT |
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| what is radiation density dependent on |
the amount of radiation reaching a particular area of the film |
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usnavalmd Mon, 16 Feb 2009 13:51:37 GMT |
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| the radiation exiting the body after attenuation |
remnant radiation |
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usnavalmd Mon, 16 Feb 2009 13:51:37 GMT |
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| resulting mass of metallic silver deposited per unit area during development |
density |
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usnavalmd Mon, 16 Feb 2009 13:51:37 GMT |
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| to lessen the amount, force, magnitude, or value |
attenuate |
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usnavalmd Mon, 16 Feb 2009 13:51:37 GMT |
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| what causes poor screen contact |
warped cassette
twisted or cracked cassette frame
loose hinges or springs
foreign bodies |
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usnavalmd Mon, 16 Feb 2009 13:46:21 GMT |
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| as the thickness of the active layer of a screen increases the image becomes what |
blurred |
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usnavalmd Mon, 16 Feb 2009 13:46:21 GMT |
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| what are the active layer thicknesses for both detail (slow) screens and fast screens |
detail screens- 50 microns
fast screens- 300 microns |
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usnavalmd Mon, 16 Feb 2009 13:46:21 GMT |
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| what increases with increased crystal size |
image blur |
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usnavalmd Mon, 16 Feb 2009 13:46:21 GMT |
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| what are the three things that impair detail of screens |
crystal size
active layer thickness
film screen contact |
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usnavalmd Mon, 16 Feb 2009 13:41:16 GMT |
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| is recorded detail better in radiography with cardboard holders or with intensifying screens |
cardboard holders |
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usnavalmd Mon, 16 Feb 2009 13:41:16 GMT |
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| what are the three ways to minimize motion |
immobilization of the part
suspension of respiration
short exposure times |
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usnavalmd Mon, 16 Feb 2009 13:41:16 GMT |
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| what is the greatest enemy of detail |
motion |
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usnavalmd Mon, 16 Feb 2009 13:41:16 GMT |
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| what increases with an increase in OID |
magnification |
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usnavalmd Mon, 16 Feb 2009 13:34:18 GMT |
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| what occurs when OID is increased with SID and EFS remaining the same |
increase in blurring and decrease in image detail |
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usnavalmd Mon, 16 Feb 2009 13:34:18 GMT |
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| what happens with a decrease of OID when EFS and SID remain the same |
decrease blur and improve detail |
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usnavalmd Mon, 16 Feb 2009 13:34:18 GMT |
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| what occurs when SID is increased and OID remains unchanged |
blurring decreases and recorded detail improves |
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usnavalmd Mon, 16 Feb 2009 13:34:18 GMT |
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| what are the two ways that focal spot blurring are caused by xrays |
1. converging toward the edge of the object
2. diverging toward the edge of the image at the film |
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usnavalmd Mon, 16 Feb 2009 13:26:34 GMT |
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| tubes with smaller focal spots provide better ______ with resulting improved image quality |
detail |
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usnavalmd Mon, 16 Feb 2009 13:26:34 GMT |
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| the size of the focal spot has a profound influence on what |
detail |
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usnavalmd Mon, 16 Feb 2009 13:26:34 GMT |
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| what are the geometric factors which influence definition |
EFS- effective focal spot
SID- source to image receptor distance
OID- object to image receptor distance |
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usnavalmd Mon, 16 Feb 2009 13:26:34 GMT |
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| a region in which the object is properly imaged, the image proper |
umbra |
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usnavalmd Mon, 16 Feb 2009 13:19:58 GMT |
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| the distance from the object to the film |
OID- object to image receptor distance |
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usnavalmd Mon, 16 Feb 2009 13:19:58 GMT |
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| a blurred region on the radiograph over which the radiologic technologist has little control, area of geometric sharpness |
penumbra |
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usnavalmd Mon, 16 Feb 2009 13:19:58 GMT |
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| the distance from the focus of the xray tube to the film |
FFD- focal film distance |
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usnavalmd Mon, 16 Feb 2009 13:19:58 GMT |
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