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Describe radiographic density
Radiographic density is the overall blackness produces on the image after processing.
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Factors that directly affect density are identified as __________. Factors that indorectly affect density are called _______________
- controlling factors
- influencing factors
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What are the two controlling factors of density?
- Milliamperage
- Exposure time
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The 11 influencing factors affecting density are
- kVp
- distance
- grids
- Film-screen speed
- collimation
- anatomic part
- anode heel effect
- reciprocity law
- generator output
- filtration
- film processing
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The product of mA and exposure time has a ______________ relationship with the quantity of x-rays produced.
direct proportional
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As the quanity of x-rays is increased, the radiographic density ____________. As the quanity of x-rays decreases, the radiographic density ____________
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_______________ and ____________ control the quantity of radiation reaching the image receptor
- Milliamperage
- exposure time
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mAs can be doubled by _____________ the milliamperage or the exposure time
doubled
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To maintain the same mAs, the radiographer must increase the ___________ and proportionally decrease ____________
- milliamperage
- exposure time
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Milliamperage and exposure time have a __________ relationship when maintaining the same mAs.
Inverse
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100 mA @ 100 ms (0.10 s)=10 mAs. To maintain the mAs, you could use
- 200 mA @ 50 ms=10 mAs
- 50 ms @ 200 ms=10 mAs
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The minimum change for needed to correct for a density error is determined by
multiplying or dividing the mAs by 2
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Making a visible change in radiographic density requires that the minimum amount of change in mAs be approximately
30%
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kVp affects radiographic density because
it alters the amount and penetrating ability of the x-ray beam
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Increasing the kVp _______the quantity of radiation reaching the IR and therefore __________the radiographic density.
increases
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Kilovoltage has a __________ relationship with density
direct
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A __________ change in kVp is needed when operating at a high kVp (greater than 90) compared with operating at a low kVp (less than 70)
greater
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Maintaining or adjusting radiographic density can be accomplished with a kilovoltage by using the ________
15% rule
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The 15% rule states that
changing the kVp by 15% will have the same effect on radiographic density as doubling the mAs, or reducing the mAs by 50%
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Increasing the kVp from 82 to 94 will have the same effect on density as
increasing the mAs from 10 to 20
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Increasing the kVp by 15% increases the radiographic density unless
the mAs is decreased
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Higher kVp will increase __________ and therefore less quantity of radiation is needed to achieve __________
- beam penetration
- a desired density
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As SID increases, the x-ray beam intensity is __________
spread over a larger area
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The inverse square law states that the
intensity of the x-ray beam is inversly proportional to the square of the distance from the source.
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As SID increases the radiographic density decreases as a result of the
square of the distance
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Because increasing the SID decreases x-ray beam intensity and the density, the ______ must be increased accordingly to maintain density
mAs
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The _____________________ provides a mathmatical calculation for adjusting the mAs when changing the SID
density maintainance formula
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The more sensitive the film screen system is to radiation _________
the fast the speed
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Increasing the fim-screen speed requires a _________ in mAs to maintain density
decrease
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Increasing collimation (smaller field size) ________ radiographic density. Decreasing collimation (larger field size) __________ radiographic density.
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A thick anatomic part ___________ the radiographic density. A thin anatomic part _____ radiographic density
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For every change in [art thickness pf 4 to 5cm, the radiographer should adjust the mAs by a factor of
2
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The reciprocity law states that the
density produced on the radiograph will be equal for any combination of milliamperage and exposure time, as long as the product of mAs is equal.
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Contrast is the degree of
difference between adjacent densities
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Radiographic contrast can be described as either
high or low
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A radiograph with few densities but greater differences among them is said to have
high contrast (short scale contrast)
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A radiogrpah with a large number of densities but little differences among them is said to have
low contrast (long-scale contrast)
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Radiographic contrast is the combined result of two catagories
film (image receptor) contrast and subject contrast
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Film, or image receptor contrast is a result of the
inherent properties manufactured into the type of film and how it is radiographed (direct exposure or with intensifying screens) along with the processing conditions.
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Subject contrast is a result of the
absorption characteristics of the anatomic tissue and the level of kilovoltage used.
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_______________ is considered the controlling factor for radiographic contrast
Kilovoltage
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_________ kilovoltage creates more densities but with fewer differences, resulting in a __________
- High
- low-contrast (long scale) image
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_____ kilovoltage creates fewer densities but with greater differences, resulting in a _________
- Low
- high-contrast (short scale) image
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At higher kilovoltages, a greater proportion of ____________ will occur compared to x-ray absorption and ____________radiographic contrast
- Compton scattering
- decreases
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Tissues with a higher atomic number ________ more radiation than those with a lower atomic number
absorb
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