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96 Cards in this Set
- Front
- Back
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The process of eliminating undesireable low energy x-ray photons by the insertion of absorbing materials in to the primary beam |
filtration |
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Are low or high energy photons eliminated with filtration? |
low |
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Does adding filtration add to or decrease patient dose? |
decrease |
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Where is the filter located? |
between the patient and the x-ray source |
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Most filters are made of this material |
Aluminum |
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How is filtration material measured? |
in mm Al/Eq |
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The amount of absorbing material that will reduce the intensity of the primary beam to 1/2 its original value |
HVL |
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What does HVL stand for? |
Half Value Layer |
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How many HVL would it take to reduce a 800 mR beam to a level of 100mR? |
3 |
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What type of filtration is built in to the tube? |
inherent |
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Filtration that take place outside the tube and housing is called___________ |
added |
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Inherent filtration usually totals between _____ and ______ for an x-ray tube. |
0.5-1.0 mm Al/Eq |
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Total filtrtation = _______ + _______ |
inherent + added |
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NCRP recommends that x-ray units using over 70 kVp use ______ mm Al/Eq |
2.5 |
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As kVp increases, the thickness of the filtration should __________ |
increase |
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a filter that uses 2 or more materials to complement one another in their absorbing abilities |
compound filters |
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Another name for compound filters |
k-edged filters |
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In a compound filter, is the filter with the highest atomic number closer to the tube or farther from the tube? |
closer |
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Specially designed filter to even out the odd shaped parts of uneven densities of the body |
compensating filter |
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An example of where a wedge filter might be used |
foot, T-spine |
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An example of where a trough filter might be used |
chest |
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an example of where a boomerang filter might be used |
shoulder, hip |
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To effectively use a compensating filter, the thickest part of the filter should be placed over the ________ dense body part |
less |
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As filtration increases, what happens to density |
decreases |
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True or false.....Secondary and Scatter radiation are the same thing |
false |
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If scatter increases, density __________ |
increases |
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If scatter increases, contrast ____________ |
decreases |
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What are the three things that can occur with an x-ray photon when it interacts with the patient? |
absorbed scatter pass through |
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2 factors that affect the amount of scatter produced |
kVp Irradiated material--size and composition |
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As kVp increases, scatter __________ |
increases |
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As kVp increases, beam intensity ________ |
increases |
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In order to have greater penetration, kVp must ________ |
increase |
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What are the two things that affect scatter production when referring to the irradiated material? |
volume and atomic # |
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As field size increases, what happens to scatter production? |
increases |
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If the atomic number increases, will we have more photoelectric interactions or compton interactions? |
photoelectric |
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As collimation increases, scatter _______ |
decreases
**increasing collimation means decreasing field size |
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Name the 4 beam restriction devices listed in class |
aperture diaphragm cones and cylinders collimator lead blocker |
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Of the four beam restriction devices which one does not affect scatter production? |
lead blockers |
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Geometric unsharpness around the periphery of the image |
penumbra |
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if you go from large to small focal spot, what happens to penumbra? |
decreases |
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As penumbra increases, resolution _________ |
decreases |
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Which has more penumbra, a diaphragm or a cylinder? |
diaphragm |
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what is the most common beam restrictor in radiography? |
collimator |
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How many sets of shutters does a collimator have? |
2 |
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Which set of collimator shutters reduce the amount of off-focus radiation reaching the film? |
upper |
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Which set of collimator shutters reduce penumbra? |
bottom |
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What does PBL stand for? |
Positive Beam Limitation |
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sensingdevice that determines the size and placement of cassette in the bucky tray |
PBL |
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Two examples of exams that a lead blocker is useful in absorbing scatter. |
Lateral L spine and Lateral T spine |
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T or F...a lead blocker helps reduce patient dose as it absorbs scatter. |
False |
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A grid has a series of ____________ lead strips which alternate with _____________ interspace material. |
radiopaque radiolucent |
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if x-rays can't pass through an object, it is _____ |
radiopaque |
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If x-rays easily pass through an object, it is _________. |
radiolucent |
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What is the purpose of a grid |
improves contrast by absorbing scatter |
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A film exhibiting low contrast shows (many/ very few) shades of grey. |
many |
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General rules for grid use |
Greater than 10cm thick Greater than 70 kVp |
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Grid ratio = |
height of lead strips/width of interspace material |
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Who invented first grid |
Gustav Bucky |
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What type of grid was the first grid? (construction) |
criss-cross |
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Who invented the the reciprocating grid? |
Hollis Potter |
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Who invented the linear grid? |
Hollis Potter |
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T or F Grids reduce scatter produced when photons reach the patient. |
F |
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The main purpose of a grid is to________ |
improve contrast |
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What is the most common material used as an interspace in grids? |
Aluminum |
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An increase in grid ratio, means there will be a(n) (increase/decrease) in scatter reaching the IR |
decrease |
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As grid ratio goes up, density _________ |
decreases |
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as grid ratio goes up and we compensate for that, what happens to pt. dose? |
increases |
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As grid ratio increases, contrast ___________ |
increases |
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The number of grid lines/ inch |
grid frequency |
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What is the minimum frequency necessary for a grid in order to avoid the Moire effect in digital imaging? |
103 lines/inch |
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As grid frequency increases, contrast ______ |
increases |
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As grid frequency increases, is more or less scatter absorbed? |
more |
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Which grid is easier to use--criss cross or linear |
linear |
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When is it ok to angle when using a grid? |
when you angle along the grid lines (length of the grid) |
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When a grid absorbs primary beam, it is called: |
cut off |
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Name the two types of linear grids |
parallel focused
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As SID decreases to very short distances, how does this affect the amount of cut off with parallel grids? |
it increases |
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Why are the lead strips in a focused grid angled? |
to match beam divergence |
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What is the focal range on a focused grid? |
the range of SID's that are able to be used |
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What is the most common grid in use today? |
Bucky system |
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What is it called when a motor moves the bucky back and forth? |
reciprocate |
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Do we need to use more mAs or less mAs when we use a grid as compared to a screen exposure? |
more |
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The grid conversion factor compares what? |
mAs with a grid/mAs without a grid |
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If we want to maintain an exposure, but have changed the grid ratio used, what formula do I use? |
mAs1/mAs2 = GCF1/ GCF2 |
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When grids absorb a greater % of scatter than primary beam, they are described as having a greater degree of __________ |
selectivity |
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contrast with a grid/contrast without a grid represents what? |
Contrast improvement factor |
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if the K (contrast improvement factor) = 1, then________ |
no improvement |
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If the tube is angled across the long axis of the grid strips, this would give a(n) ________ grid error |
off-level |
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If the Centeral Ray is not directly in the middle of a focused grid, this will cause a(n) ______ grid error |
off-centered |
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For an off-centered grid error, what is the result on the image? |
decrease in density across entire image |
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For an off level grid error, what is the result on the image? |
decrease in density across entire image |
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If a radiograph is taken using a focused grid with a focal range of 35-44 inches, but a 60" SID is used, what is the result on the image? |
decrease in density mainly at edges |
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What is the result on the image if the focused grid is accidentally used upside down? |
decrease in density at the edges |
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what is is called if the grid lines interact with the pixel rows or columns on a digital system? |
Moire effect |
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With this technique, the amount of scatter reaching the IR decreases, but there is magnification of the image. |
Air-Gap Technique |
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If there is a 10" air gap used, there will be a similar result in scatter clean up to a ____ grid |
15:1 for a 10cm body part |
