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58 Cards in this Set
- Front
- Back
Scatter is Primarily the Result of? |
Compton effect |
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What factors affect the Amount and Energy of Scatter? |
kVp and tissue volume |
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What are the effects of Increased kVp on photoelectric effect, penetration and Compton effect? |
increased x-ray transmission
reduced photoelectric interactions increased Compton effect |
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What are the purposes of Beam Restriction? |
limits patient exposure
reduces scatter |
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What is the effect of a Beam Restricting Device? |
changes shape and size of primary beam
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What are the effects of Collimation on scatter, contrast and exposure technique? |
decreased scatter
increased contrast may require increased exposure techniques of 30-50% |
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What materials are used to Construct Collumators? |
metals that readily absorb x-rays |
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Descript an Aperture Diaphragm. |
flat piece of lead that has a hole (aperture) in it
causes large areas of unsharpness on perimeter of radiograph |
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Describe the Structures of Cones and Cylinders |
aperature diaphragm with extended flange
flange can also be telescoping |
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What are the advantages of Cones and Cylinders? |
reduce unsharpness (cylinders are better)
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What is the Effect of the Angle of the Flange of the Cone? |
if cone angle is too great it then only acts as an aperture diaphragm |
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Describe the construction and features of a Collimator. |
has multiple lead shutters which allow adjustment in the projected fields
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What is an Automatic Collimator? |
also called a positive beam-limiting device |
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Describe the features of a Grid and its effect on exposure. When should grids be used? |
device with thin lead strips with radiolucent interspaces used to absorb scatter
using a grid requires additional mAs usually used whtn anatomic part is greater than 10 cm |
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What effect does a Grid have on Contrast? |
increases contrast
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What are the characteristics and purpose of Interspace Material on a grid? |
radiolucent material that separates lead strips
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What is Grid Frequency? |
expresses number of lead lines per unit length
Ex: 30 lines/cm |
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What is the Grid Ratio and how is it calculated |
height of lead strips divided by distance between strips |
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What is the effect of High Grid Ratio grids? |
Increase contrast |
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What type of Grid Patterns are available |
linear and cross-hatched
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Advantages/Disadvantages of Cross-Hatched Grids |
remove more scatter
x-ray tube cannot be angled |
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What types of Grid Focus are available? |
parallel (nonfocused)
angled (focused) |
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What is meant by the Convergent Point? |
point of x-ray origin from tube |
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What is meant by the Convergent Line of a grid |
points connected alont the length of the grid |
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What is Focal Distance (grid radius) of a grid? |
distance between the grid and the convergent point |
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What is the Focal Range of a grid? |
recommended range of the SID that can be used with a focused grid
Ex: 36-42 inches |
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Where is a Wafer Grid placed? |
matches the size of the cassette and is taped to the top of the IR
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What is a Grid Cassette? |
IR with grid permanently mounted to front surface |
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What is a Grid Cap? |
a permanently mounted grid that allows IR to be mounted behind it
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What are Stationary Grids? What are their disadvantages? |
possible to see grid lines on the image
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What are Reciprocating Grids? What are their advantages? |
makes grid lines less visible |
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What is the Potter-Bucky Diaphragm? |
a reciprocating grid located just above tray holding the IR
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What is a Long-Dimension Grid? |
has lead strips running parallel to the long axis of the grid |
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What is a Short-Axis Grid? |
has lead strips running perpendicular to the long axis of the grid
used where it is difficult to center the central ray along the long axis |
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Grid Conversion Factor (Bucky Factor) |
used to determine the adjustment in mAs needed when using a grid |
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What formula is used when calculating exposure when using different grid factors? |
mAs1 GCF1 |
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What is Grid Cutoff and what causes grid cutoff? |
decreased number of transmitted photons reaching the IR because of grid misalignment |
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What are the 4 Types of Grid Cutoff? |
1) upside-down focused grid - both sides of image very underexposed
2) off-level grid (tilted) - appears as exposure loss 3) off-center grid - one side of image underexposed 4) off-focus grid - both sides of image underexposed |
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What is Moire Effect? What causes the Moire Effect? |
a zebra-pattern created when a stationary grid is used during computed imaging
results from the grid frequency being similar to the laser scanning frequency during image processing |
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What is Air Gap Technique? What can be done to decrease magnification? |
scatter is reuced with an increased OID |
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What are the characteristics of the typical grid? |
Linear (not crossed) Focused (not parallel) Mid-ratio (8:1 to 12:1) Has a focal range of 40 - 72" |
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The projected shape of the unrestricted primary beam is: A) square B) rectangular C) circular D) elliptical |
C |
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A purpose of beam-restricting devices is to __________ by changing the size and shape of the primary beam. A) increase patient dose B) decrease scatter C) increase IR exposure D) decrease image contrase |
B |
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The most effective type of beam-restricting device is the: A) cone B) aperture diaphragm C) cylinder D) collimater |
D |
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Of the beam-restricting devices, which two are most similar: A) cone & aperture diaphragm B) cone and cylinder C) aperture diaphragm & cylinder D) aperture diaphragm & collimator |
B |
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The purpose of automated collimation is to ensure that: A) the quantity of scatter production is minimal B) the field size does not exceed the IR size C) maximal recorded detail and contrast are achieved D) exposure to the IR is maintained |
B |
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When making a significant increase in collimation,: A) mAs should be increased B) kVp should be increased C) mAs should be decreased D) mAs should be increased |
A |
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Which of the following increases as collimation increases? A) Patient exposure B) Scatter production C) Fog D) Contrast |
D |
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Which of the following statements is true of positive beam-limiting devices? A) They are required on all radiographic installations B) They are required on all new radiographic installations C) They have never been required on radiographic installations D) They were once required on new radiographic installations |
D |
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The purpose of a grid in radiography is to: A) increase IR exposure B) increase image contrast C) decrease patient dose D) increase recorded detail |
B |
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Grid ration is defined at the ratio of the: A) height of the lead strips to the distance between them B) width of the lead strips to their height C) number of lead strips to their width D) width of the lead strips to the width of the interspace material |
A |
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As compared to parallel grids, focused grids: A) have a greater grid frequency and lead content B) can be used with either side facing the tube C) have a wider range of grid ratios and frequencies D) allow more x-ray photons to reach the image receptor |
D |
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If 15 mAs is used to produce a particular level of exposure to the IR without a grid, what mAs would be needed to produce that same level of exposure using a 16:1 grid? |
90 |
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Grid cutoff, regardless of the cause, is most recognizable on a radiograph as reduced: A) contrast B) recorded detail C) density D) positioning |
C |
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Off-focus grid cutoff occurs by using an SID that is not: A) within the focal range of the grid B) equal to the focal distance of the grid C) at the level of the convergent line of the grid D) at the level of the convergent point of the grid |
A |
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The type of motion most used for moving grids is: A) longitudinal B) reciprocating C) circular D) esingle stroke |
B |
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A grid should be used whenever the anatomic part size exceeds: A) 3 cm B) 6 cm C) 10 cm D) 12 cm |
C |
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The air gap technique uses a increased ________ instead of a grid. A) kVp B) mAs C) SID D) OID |
D |