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Ch.15 Beam Restriction

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kkaitlyn96's version from 2017-03-08 01:00

Section 1

Question Answer
what are 4 things that filtration does?1.reduce patient dose 2. alters characteristics of the beam 3. affects density and contrast 4. affects the amount of scattered radiation produced
As filtration increases, photons _________ and density _________decrease, decrease
What is scatter radiation?Primary radiation that loses energy and changes direction
When is scatter radiation produced?Produced in the body, when the photons undergo comptons scatter
When matter is increased then scatter is _________increased
Why is more scatter created when the part is thicker?Because there are more atoms to interact with
What are the prime factors that affect scatter?kVp and irradiated material
memorize

Section 2

Question Answer
What kind of relationship does volume have with scatter?direct; as volume increases, scatter increases
What kind of relationship does atomic number have with scatter?indirect
When atomic number increases, scatter _________decreases
What kind of relationship does mass density have with scatter?indirect
When mass density increases, scatter__decreases
memorize

Section 3

Question Answer
What is the primary purpose of beam restricting? (3 things)1. Improve image quality 2. decrease scatter 3. decrease exposure to patient
How does beam restricting work?decreases photons
Beam restricting= less photons =__irritated tissue,__dose,__scatterdecrease irritated tissue, decrease dose, decrease scatter
When scatter is decreased contrast is _________increased
Contrast= more or less grayless gray
memorize

Section 4

Question Answer
If field size decreases, number of photons _________decreases
Field size decreases, scatter _________decreases
Field size decreases, density _________decreases
Field size decreases, contrast _________increases
When scatter is decreased, density is _________ decreased
memorize

Section 5

Question Answer
If density changes then what technical factor needs to be changed?mAs
14x17 to 10x12 increase mAs by _________%25
14x17 to 8x10 increase mAs by _________%50
memorize

Section 6

Question Answer
How does a collimator work?led shutters at right angles that move symmetrically from the center
Collimator is also called variable aperture diaphragm
what is Positive beam limitation an automatic collimator
How does positive beam limitation work?sensing devices in the bucky tray activate a motor that drives the collimator
What does the top shutter of the collimator do?reduce off focus radiation
What does the bottom shutter of the collimator do?reduce penumbra
What is penumbra?unsharpness around an image
Decrease in penumbra= _________ in detailincrease
memorize

Section 7

Question Answer
What is an aperture diaphragm? flat sheet of metal, hole in middle
Equation for projection image size:SID*lower diameter / distance from focal spot
What is two disadvantages to aperture diaphragm?Increase penumbra and Increase off focus radiation
Cones/ Cylinders can also be called position indicating devices
extension coneseither flares or diverges
Cylindersdo not flare, have the same diameter throughout
Two advantages to Cones/ Cylinders aredecrease penumbra and decrease off focus radiation
memorize

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