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28 Cards in this Set
- Front
- Back
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Screen phosphors should have
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1. a high atomic number
2. high conversion efficiency 3. light matched to film used 4. minimal afterglow |
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Emulsion
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primarily silver halide crystals in gelatin
May be coated on one or both sides of the film Emulsion speed is a function of grain diameter or surface area |
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k-edge absortion and intensifying screens
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all rare earth materials have atomic numbers < tungsten
therefore, all K shell EBF are less than tungsten this is why rare earth phosphors absorb more photon energy than calcium tungstate use KVP values that exceed the K shell EBF for your screens, usually over 60 KVP |
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the random distribution of a small number of photons over the surface of the intensifying screen and film
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quantum mottle
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Noise or graininess
How it’s created: very fast film/screen combinations and high frequency generators How to find it: look on a full spine radiograph of a thin patient in the region of the liver |
quantum mottle
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4 parts of screen
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protective coating
phosphor layer reflective layer base |
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importance of Reflective layer in screen
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light is produced isotropically
takes light produced by screen moving away from the film and directs it toward the film increases the speed of the screen by doubling the number of photons reaching the film |
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importance of base:
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provides mechanical support for phosphor layer
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Flat (tabular grains) purpose in film:
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offer a larger cross section with more light gathering capability than conventional grains
Tabular grains are more tolerant to developer activity (more forgiving) |
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Emulsion speed is a function of
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of grain diameter or surface area
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which is advantages of duplitizing film over single emulsion film?
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faster
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the blue dye in a film emulsion helps to
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reduce eye fatigue in reading films
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which will increase contrast
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decrease kvp
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function of screen inside cassette is
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reduce patient exposure.
emit light to be absorbed by film. |
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k edge absoprtion:
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use KVP values that exceed the K shell EBF for your screens, usually over 60 KVP
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international community uses gray (Gy) and sievert (Sv)
what are they? |
gray is patient dose
sievert is occupational exposure |
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Do I need to adjust the tube’s position when using a 15 degree tube tilt at 40”? This AP lower cervical technique requires an exposure dose of 15 mr for a proper exposure
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yes use inverse square law
should get 14 % decrease |
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Velocity of light
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3 x 108m/s
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why phosphor thickness for films
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The thicker the phosphor layer, the higher the number of x-rays converted to light.
High speed screens have thick layer. Detail screens have a thin layer. |
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purpose of crystals in screen
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Larger crystal produce more light per interaction. Detail screens have small crystals.
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purpose of spatial resolution
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Image detail is the result of spatial resolution and contrast resolution.
Generally the conditions that increase speed reduce spatial resolution. |
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what is the focal spot
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is the area of the anode from which the x-rays are emitted.
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The angling of the target is know as
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line focus principle
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By angling the anode target, one makes the the effective focal spot ____than the actual area of interaction
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much smaller
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is the beam projected onto the patient.
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effective focal spot
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as the anode angle decreases
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the effective focal spot decreases.
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The advantage of Line focus
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provides the sharpness of the small focal spot with the heat capacity of the large large focal spot.
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Tube life is extended by
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Use of minimum mAs & kVp appropriate for the exam.
Use of faster images receptors require lower mAs and kVp. They extend tube life |
