Study RAD Technique Test 3 Flash Cards

 
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RAD Technique Test 3

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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
what is photographic effect used for
to figure out which technique has the greatest or least density
what is the formula for magnification
MF= SID/OID
what is the formula for photographic effect
PE = mA x time x kVp2 / distance2
use of beam restriction devices will do what to contrast
increase
increased mAs = __________ contrast
decreased
increased grid ratio =_________ contrast
increased
what are the two major characteristics of image that directly influence the diagnostic quality of the radiograph
density
contrast
the difference in optical density on a radiograph
radiographic contrast
the amount of black metallic silver deposited per unit area during development
radiographic density
what are the anatomical structures ranging from greatest to least mass density
dental enamel
bone
tissues of water density
fat
gases
what is the controlling factor in contrast
kV
the apparent displacement of an object when viewed from different vantage points
parallax
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
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
what is the formula for determining contrast improvement of a grid
k= radiographic contrast w/ the grid /
radiographic contrast w/out the grid
what is the formula for determining selectivity of a grid
selectivity=
% primary radiation transmitted /
% scatter radiation transmitted
what are the two functional factors of efficiency of radiographic grids
selectivity
contrast improvement factor
what happens to the grid frequency when the lead strips are thin
the frequency goes up
what is the frequency range for grids
20-40 lines per centimeter
50-100 lines per inch
what are the two benefits of a higher grid ratio
better cleanup of scatter radiation
increased radiographic contrast and improved detail
what is the formula for figuring grid ratio
r=h/D
grid ratio=height of lead strips/width of spaces between the strips
what are the two physical factors that effect the efficiency of radiographic grids
grid ratio
grid frequency
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
with what type of grid is centering and distance not critical
parallel grid
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
the height divided by the inter space thickness
grid ratio
the number of grid strips or grid lines per inch or per centimeter
grid frequency
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
if an object is placed lateral to the center of the xray beam what two results may occur
magnified (elongated)
foreshortened
what are the two factors that effect magnification
SID & OID
what are the two factors that determines distortion on a radiograph
size (magnification)
shape
the amount of reduction in image size
foreshortened
unequal magnification of different portions of the same object
distortion
what are the factors that effect subject contrast
kV
effective atomic number of the body part
patient thickness
tissue mass density
object shape
radiographic contrast is designated as what
long scale ( low contrast )
short scale ( high contrast )
the difference in optical density on a radiograph
contrast
structures that absorb xrays
radiopaque
structures that attentuate (stop) xrays to a relatively small degree
radiolucent
an undesirable fluctuation in optical density of the image
radiographic noise
what body structure has the greatest density
dental enamel
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
what happens to the radiographic exposure rate as SID increases
exposure rate decreases
what determines only exposure rate and has nothing to do with the penetrating power of the beam
mA
what does doubling mA do to exposure rate
doubles radiographic exposure rate
xray output (R/min) is proportional to what
mA
an increase of kV by 15% does what
doubles the exposure
increase in kV equals what
increase of remnant radiation reaching the intensifying screen
what are the five factors that govern radiation exposure and resulting density
kVp
mA
time
SID
radiographic object
what is an extremely important factor in radiation quality
density
what is radiation density dependent on
the amount of radiation reaching a particular area of the film
the radiation exiting the body after attenuation
remnant radiation
resulting mass of metallic silver deposited per unit area during development
density
to lessen the amount, force, magnitude, or value
attenuate
what causes poor screen contact
warped cassette
twisted or cracked cassette frame
loose hinges or springs
foreign bodies
as the thickness of the active layer of a screen increases the image becomes what
blurred
what are the active layer thicknesses for both detail (slow) screens and fast screens
detail screens- 50 microns
fast screens- 300 microns
what increases with increased crystal size
image blur
what are the three things that impair detail of screens
crystal size
active layer thickness
film screen contact
is recorded detail better in radiography with cardboard holders or with intensifying screens
cardboard holders
what are the three ways to minimize motion
immobilization of the part
suspension of respiration
short exposure times
what is the greatest enemy of detail
motion
what increases with an increase in OID
magnification
what occurs when OID is increased with SID and EFS remaining the same
increase in blurring and decrease in image detail
what happens with a decrease of OID when EFS and SID remain the same
decrease blur and improve detail
what occurs when SID is increased and OID remains unchanged
blurring decreases and recorded detail improves
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
tubes with smaller focal spots provide better ______ with resulting improved image quality
detail
the size of the focal spot has a profound influence on what
detail
what are the geometric factors which influence definition
EFS- effective focal spot
SID- source to image receptor distance
OID- object to image receptor distance
a region in which the object is properly imaged, the image proper
umbra
the distance from the object to the film
OID- object to image receptor distance
a blurred region on the radiograph over which the radiologic technologist has little control, area of geometric sharpness
penumbra
the distance from the focus of the xray tube to the film
FFD- focal film distance
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