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x-posure/scatter
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Question | Answer |
---|---|
remnant x-rays are those that? | exit the patient |
what factor(s) that affects scatter radiation can be controlled by the technologist? | field size |
as kVp increases, scatter _______ | increases b/c there is less compton interaction |
what percent of x-rays are transmitted through a patient? | 1% |
at a high kVp (125kVp), most x-rays are? TRANSMITTED THRU THE BODY WITH INTERACTION or TRANSMITTED THRU THE BODY WITHOUT INTERACTION | transmitted thru the body with interaction |
increasing kVp while decreasing mAs decreases what? | patient dose |
if a constant optical density is maintained while kVp in increased what happens to patient dose? | decreases |
as field size increases, what happens to scatter? | increases |
scatter radiation reduces radiographic quality by changing? CONTRAST, DISTORTION, OPTICAL DENSITY, MASS DENSITY | contrast |
x-rays that the tech would like to have interact with the IR are those that are? | transmitted in the body |
an increase of kVp from 70 to 80? RESOLUTION IMPROVED, SID MUST BE INCREASED, HIGHER PROPORTION OF SCATTER, LOWER PROPORTION OF SCATTER | higher proportion of scatter |
an increase in kVp from 70 to 90, while other factors remain constant result in? INCREASED DETAIL, DECREASED # OF ABSORBED RAYS, INCREASED # OF ABSORBED RAYS | # of absorbed rays decreases |
what increases as the field size of the beam increases? QUANTUM MOTTLE, SCATTER, MAGNIFICATION | scatter |
as thickness of the anatomy increases what factor increases? mAs, kVp, SID, OID | kVp |
which process is most responsible for the production of scatter? PHOTOELECTRIC EFFECT, COMPTON EFFECT, TRANSMISSION | compton effect |
which is not a beam-restricting device? CONE, APERTURE DIAPHRAGM, PBL, ADDED FILTRATION | added filtration |
an aperture diaphragm allows x-rays to expose an area? | a size just smaller than the IR |
when an aperture diaphragm is used cutoff can occur when? | the diaphragm is not properly positioned |
which is the most simple of all beam-restricting devices? CONE, ALUMINUM FILTER, APERTURE DIAPHRAGM | aperture diaphragm |
off focus radiation occurs when? | projectile electrons do not strike the focal spot |
cones and cylinders are used primarily to reduce? | scatter |
a decrease in field size will result in? | decrease in radiographic density, decrease in scatter within the patient |
factors that influence scatter in image forming beam? | kVp, field size, pt thickness |
TRUE OR FALSE soft tissue absorbs more radiation and produces more scatter than bone? | false |
what is the purpose of bean limiting devices? | control scatter |
principle reason for using a grid? | improve image contrast |
which material is the most radiolucent? ALUMINUM, CARBON FIBER, COPPER, LEAD | carbon fiber |
what is the most important grid characteristic? | grid ratio |
if only scatter reached the IR the image contrast would be? | very low |
grids are principally effective in attenuating which of the following? photoelectrons, remnant radiation, x-rays after compton interaction, x-rays after photelectric interactions | x-rays after compton interaction |
if the interspace dimension is constant, increasing the grid ratio will? | make the grid thicker |
as grid frequency increases what happens with the grid strips? | # of strips/cm increases and interspace width becomes thinner |
use of which will reduce radiographic contrast? COLLIMATORS, FILTRATION, GRIDS, INTENSIFYING SCREENS | filtration |
which is the best grid material in terms of x-ray attenuation? COPPER, IODINE, TUNGSTEN, URANIUM | uranium |
which will not improve image contrast? DECREASE KvP, GRID, ADDED FILTRATION, COLLIMATING DOWN | added filtration |
which are more effective, high grid ratios or low grid ratios? | high grid ratios |
efficiency of a grid to reduce scatter is related to? GRID FREQUENCY, GRID INTERSPACE, GRID RATIO | grid ratio |
which is the least important indicator of grid performance? GIRD FREQUENCY, GRID MASS, GRID STRIP HEIGHT, GRID RATIO | grid strip height |
the contrast improvement factor is defined as the x-ray contrast obtained ______ | with a grid compared to that obtained without a grid |
in general, the selectivity of a grid depends on which? CONTRAST IMPROVEMENT FACTOR, FOCAL LENGTH, GRID FREQUENCY, GRID MASS, GRID RATIO | grid mass |
x-ray grids with high contrast improvement usually effects resolution by? | improving contrast resolution |
which is the simplest type of grid? CROSSED GRID, FOCUSED GRID, LINEAR GRID, | linear grid |
undesirable absorption of image-forming x-rays by a grid is called? | grid cutoff |
one factor that does not affect the percentage of scatter that reaches the IR? GRID MASS, GRID RATIO, kVp, mAs, PATIENT THICKNES | mAs |
which of the following would reduce production of scatter? DECREASE IN FIELD SIZE, DECREASE IN SID, DECREASE IN OID, FILTER, GRID | decrease in field size |
what kind of grid reduces scatter along two axes? | crossed grid |
what is a disadvantage of a moving grid? | may produce blur |
when the air-gap technique is used, what happens to resolution? | contrast resolution is improved |
when the air-gap technique is used, what happens to patient dose? | increased patient dose |
what happens if you replace an 8:1 grid with a 12:1 grid? | greater positioning latitude |
which has the greatest contrast improvement factor? CROSSED GRID, FOCUSED GRID, MOVING GRID, PARALLEL GRID | crossed grid |
scatter photons increase contrast? TRUE OR FALSE | false |
as irradiated tissue volume increases, scatter increases? TRUE OR FALSE | true |
if the height of the grid is constant and distance is decreased between the lead strips there would be an increase in grid ratio? TRUE OR FALSE | true |
cross-lateral grids are commonly used in clinical practice? TRUE OR FALSE | false |
a focus design results in a grid with strips designed to match the divergence of the x-ray beam? TRUE OR FALSE | true |
if the x-ray tube is not centered on the central axis of the focus grid, it is termed lateral re-centering? TRUE OR FALSE | true |
off focus errors result in grid cut off along the peripheral edges of the IR? TRUE OR FALSE | true |
utilizing the air-gap technique will increase the amount of scatter reaching the radiograph itself? TRUE OR FALSE | false |
what is known as the degree of difference of optical density between areas of the image? | contrast |
contrast on a radiographic image is highest when the amount of __________ scatter is the lowest | compton |
grids remove scatter before the beam reaches the ________ | IR |
amount of grid scatter depends on what 3 factors? | 1-angle of scattered photons 2-height of grid strips 3-width of grid strips |
what is the grid ratio? | height/distance |
a grid with good clean-up will remove what percent of scatter? | 80-90% |
grid frequency is how many lines/inch? | 60/110 |
pt dose and technical factors increase proportionally with the _________ factor | bucky |
main disadvantage of using a parallel grid? | grid cut off |
with tech factors over 90 kVp, it is best to sue grids with what ratios? | 8:1 |
photons that pass through the body unaffected produce? | radiographic contrast |
photon absorption within the body results from? | photelectic interactions |
a grid is made of thin __________ ______ strips and ___________ fillers that are aligned with the beam | radiopaque lead, radiolucent |
which grid would have the greatest distance between strips? | 6:1 |
the purpose of a moving grid? | to blur grid lines |
amount of scatter increases with what 3 things? | increase in pt thickness, increase in field size, decrease in atomic # |
as kVp increases, contrast _________, scatter _______ and IR exposure _________ | contrast decreases, scatter increases, IR exposure increases |
angulation of the long axis of a linear grid will cause? | grid cut off |
amount of scatter radiation is affected by? | collimation and kVp |
grid cut off and off centering results in ______ of density | loss |
grid cut off is more pronounced with high- ratio grids or low-ratio grids? | high-ratio grids |
what is the result of replacing an 8:1 grid with a 12:1 grid? | greater positioning latitude |
besides an exam needed a wide rang SID, which grid would most likely produce grid cut off? 5:1 6:1 8:1 12:1 16:1 | 16:1 |
when the air gap technique is used, what happens to contrast resolution? | improves |