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52 Cards in this Set
- Front
- Back
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What is the ovarall blackening of a radiographic image called?
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Density
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What causes Density on a radiographic image?
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It is caused from black metallic silver, dued to exposure and processing.
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List the 2 properties that effect visibility of detail.
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Density and Contrast
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What is visibilty of detail?
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A radiographic image that is visible to the human eye only, b/c and optimal amount of density and contrast exists on the image.
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What are the other names for Density?
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Optical Density (OD), and Lograrithm of Opacity
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What is the ratio of the amount of light transmitted through the film called?
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Optical Density
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When the light strikes the film from the back it is referred to as the ______ ?
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Light Indicator (Io)
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The light that is seeen coming through the radiograph is called the _____ ?
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Light Transmitted (It)
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What is the formula for Optical Density?
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OD=Log10 x (Io/It)
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Light Transmitted Table
Percent-Fraction-OD# _______ ________ 0 _______ ________ 1 _______ ________ 2 _______ ________ 3 _______ ________ 4 |
Percent-Fraction
100 1 10 1/10 1 1/100 0.1 1/1000 0.01 1/10000 |
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What do mAs control and how is it related to Density?
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mAs control quantity and are directly proportional to Density.
*mAs double, Density doubles |
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How are mA and time related?
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Inversely
*mA increases, Time decreases |
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What is the Reciprocity Law?
*Remember ASS |
ANY combination of mA and Time will produce the SAME mAs value and will result in the SAME density on a radiograph.
*mAs=mAs |
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When will the reciprocity law fail?
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If exposure time is too quick (10ms) or is too long (5secs)
*Remember mA must be increased or decreased by 30% to change ddensity. |
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What is the useful diagnostic range?
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0.25-2.5
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What are the axis names on the OD chart?
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Y-axis=Density
X-axis=Relative Exposure Time |
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What is the preferred region for diagnostic on the OD chart?
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Straight-Line region
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What does kVp control?
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It controls quality of x-rays produced.
*But is the only factor that can control quantity and quality. |
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What is kVps relationship to Density?
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Direct but not Proportional.
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How do you find HU for a half wave or a full wave?
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mA x Time x kVp
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How do find HU for a 3 phase 6 pulse?
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mA x Time x kVp x 1.35
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How do find HU for a 3 phase 12 pulse?
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mA x Time x kVp x 1.41
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How do you find HU for a High Frequency?
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mA x Time x kVp x 1.45
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At what % does kVp increase density for a HW or FW?
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15%
*increase x by 1.15 decrease x by .85 |
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For a 3 phase 6 or 12 pulse it takes a ____% increase.
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12
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For a High Frequency it only takes a ____% increase.
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10
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It only takes a ___% increase to see a visible change.
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4
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As kVp _______, density will _______.
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increase, decrease
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A 15% ______ in kVp will double density. A 15% ______ will cut density in half.
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increase, decrease
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How do increase kVp?
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x orginal kVp by 1.15
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How do you decrease kVp?
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x kVp by .85
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How do compensate mAs when kVp increases by 15%?
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x mAs by .5
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How do you compensate mAs when kVp decreases by 15?
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x mAs by 2
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What will happen to the wavelength if kVp increases?
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They become shorter and energy increases.
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What are the x-rays that reach the film called?
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Remnant Radiation
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How is Film Speed related to Density?
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Directly Proportional
*RSS doubles, Density Doubles |
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How is Film Speed determined?
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By the thickness of the emulsion layer and size of the halide crystals.
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How is ISS determined?
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By thickness of the phosphor layer and the size of phosphor crystals.
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How are grids related to Density?
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Inversely
*grid ratio increases, Density decreases |
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How is collimation related to Density?
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Inversely
*tighter collimation, decrease Density |
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How do the anatomic structures affect Density?
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Inversely
*more tissue, decrease density Tissue-traits density thickness atomic # |
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How do additive diseases affect density?
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It decreases density.
*adjust kVp b/c of fluid viscosity |
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Partial Absorption is known as __________ ?
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Attenuation
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How do destructive diseases affect Density?
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It increases it b/c of beam attenuation.
*adjust mAs |
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High atomic weight that increases organ density and absorbs more radiation and decreases in film density so you can't see through it, so it is unchanged is known as what?
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Radiopaque
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A low atomic weigth that decreases organ density and absorbs less radiation and causes a greater film density and can be seen through and is rapidly absorb is known as what?
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Radiolucent
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How would you adjust mAs or kVp for a small to medium Plaster Cast?
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Increase mAs by 50%-60% or kVp to 5-7
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How would adjus for a large Plaster Cast?
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Increase mAs 100% or kVp 8-10
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What about for a Fiberglass Cast?
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Increase mAs 25%-30% or kVp 3-4
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What kind of affect does the anode heel affect have on density?
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None.
*Density is greater on the Cathode side. |
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How do filters affect Density?
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None.
*contrast will decrease when filtration increases. *Inherent filtration is .5-1.5 Above 70 kVp is 2.5 |
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How does processing affect Density?
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Increase in temerature
Increase in Time Increase in replenish rate |
