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33 Cards in this Set
- Front
- Back
Radiographic density
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The degree of blackness on a radiograph.
Dark areas made p of black metallic silver on finished radiograph Can be increased by raising mA or exposure time or even kVp by increasing the penetrating power of the x-ray beam |
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Radiographic Contrast - What is it? Long scale vs short scale?
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Differences in radiographic density between adjacent areas on radiograph.
Radiographic contrast depends on: -Subject density -kVp level (Higher kVp, the longer the scale of contrast) -Film contrast (The ability of film to produce long/short scale contrast) -Film fogging Long scale contrast - Few black and white shades with many shades of gray. Short scale contrast - Black and white shades with only a few shades of gray in between |
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Subject density
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The ability of the different tissue densities to absorb x-rays. Penetrate depending on the differences in atomic number and thickness
From least dense to more dense.... -Air -Water -Fat or muscle -Bone -Metal |
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Radiographic detail
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Sharp tissue and organ inteerfaces. Most common factors affecting detail are patient motion or penumbra effect
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Penumbra Effect (Penumbra)
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Excessive penumbra causing blurring around edges or shadows cast by x-ray exposure. GREATEST ON CATHODE SIDE OF IMAGE BECAUSE THE EFFECTIVE FOCAL SPOT IS NOT CONSTANT ACROSS THE RADIORAPH (Larger at the cathode)
Changes to three main ffactors that affect the amount of penumbra are: -Size of focal spot (smaller, less distortion) -Focal film distance (increased, penumbra/distortion decreased) -Object film distance (increased, penumbra/distortion increased) |
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Quantum mottle
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Density variation caused by incomplete exposure of film.
Usually result of low mA Increasing quantum mottle decreases detail |
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x-ray production process
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-Thermionic emission (Boiling off of electrons from the filament on cathode side. As filament current increases the filament becomes hotter and more electrons are relased)
-Application of high voltage (at the anode) -Acceleration of electrons to the anode -Sudden slowing/stopping of electrons (causes heat and x-rays to be generated) |
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Milliamperage
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AKA Tube current - Measurement of the number of electrons traveling from cathode to anode during the exposure
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Time
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measurement of how long the x-rays are produced - the length of exposure
Directly proportional to the number of electrons crossing the tube and is therefore directly proportional to the number of x-rays created |
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mAs calculations
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-mA x seconds = mAs
-mAs / seconds = mA -mAs / mA = seconds |
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Factors affecting Radiographic/Optical Density (OD)
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-mAs
-kVp -FFD -Intensifying screens -Grids -Structure -Generator type -Beam restrictions -Anode heel effect -Processing |
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Kilovoltage
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AKA Object Density
Measure of the maximum electrical potential across an x-ray tube Controls penetrability (The thicker the part, the higher the kVp) |
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How does kVp affect the tube current?
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increase causes an acceleratin of electrons:
-Increases electron kinetic energgy -Increases photon energy -Increase acceleration (more peneratrability) -Increase in scatter radiation Higher kVp allows you to use less mAs, decreasing tube load and tube heat |
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How does kVp affect CONTRAST
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Contrast decreases with increased kVp because it increases x-ray energy,increases penetration, and increases scatter radiatin.
-Low kVp (bone) - High contrast, less penetration, more absorption with SHORT GRAY SCALE -High kVp (abdomen) - Low contrast, more penetration, less absorption. LONG GRAY SCALE |
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How does kVp affect density?
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Increases with increased kVp due to x-ray energy
-increased penetration, increased scatter radiatino. More photons reach the film> density increased Increasing by 20% = double radiographic density Decrease by 16% = Halve the radiographic density |
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How does kVp affect exposure latitude?
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High contrast (Black and white) - is narrow latitude, at lower kVp, an error of a few kVp can make a very noticeable diffference
Low contrast (more gray) - wide latitude, difference of a few kVp will make little, if any difference |
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Scatter radiation
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Produced when x-ray photons from the primary beam redirected after interaction in/on the patient or table.
-longer wavelength, low energy x-ray photon -Not useful to image -Decreases contrast -Degrades visiblity or detail -Likely to be absorbed by next object it strikes |
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The grid
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Device used to improve the contrast of the radiographic image by cleaning up scatter radiation before it reaches the image.
-W/O a grid, scatter contributes to 50 - 90% of the image exposure. Reccomended for parts about 10 cm in thickness or greater and when using kVp at or above 60 -MOST COMMON ONE USED IN VETERINARY MEDICINE IS 8:1 |
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Air gap
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Has same effect as grid by controlling scatter because the scatter photon diverges beyond the borders of the film. Equivalent to a 5:1 grid
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Completely clear image vs black image
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Completely clear = Wasn't exposed
Black = was exposed to light, overexposed |
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Distortion
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Incorrect positioning;
-Elongation: Lengthens lenth of subject -Foreshortening: shortens length of subject (bring parallell to cassette) -Magnification: Subject appears larger (shorten OFD) -False narrowing of vertebrae (make parallel to cassette and pad under neck and between stifles) |
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Intensiffying screen construction
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Base - Plastic cardboard backingg and flexible
Reflecive layer - Made of titanium dioxide, reflects light back towards the film Phosphor layer - Light emitting crystals made of either calcium tungstate or rare earth phosphors. Increases ability to conver x-ray to light |
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Screen speeds
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Slow (detail or fine) - high defenition, better detail
Par (Medium) - Good resolution, minimum exposure High (regular) - Fast speed, used where more exposure is requred for thick tissue. Can reduce patient exposure, but is grainy. SCREEN SPEED IS INVERSLY PROPORTIONAL (THE OPPOSITE OF) THE EXPOSURE TIME |
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Large and small crystals
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Larger crystals - Faster but decrease detail
Smaller crystals = Slower but better detail |
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What is Film made up of?
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Made up of a polyester base, ligght sensitive emulsion (gelatin) on both sides, AND Silver Halide microcrystals imbedded in the gel (Silver bromide and silver iodine crystals)
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Latent image
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The image of film before developing
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Screen types
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Blue senstive (ultraviolet) - Blue light emitting phosphors from the screen (Calcium tungstate and some rare-earth phosphors)
Green Sensitive - Green light emitting posphors from sscreen (rare earth phosphors, fast and use less mAs and kVp) Non screen film (Direct exposure) - Dental x-rays (exposure through direct action of x-ray and have great detail. Plastic or paper inlight proof packet) |
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System speed
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Screen speed combined with film speed
100 = Slow speed (high detail) 200 = par medium speed 400 - 800 = high speed (less detail) 400 most commonly used in veterinary medicine |
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Film speed
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higher the number the faster the film.
SLow speed 100 - Smaller SH crystals, longer exposure time, great definition, greatest latitude in exposure and processing Medium (par) speed 200 - Compromise between time and exposure High speed 400 - 800 - larger SH crystals, grainier. Shorter exposure time with more latitude in exposure and developing |
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Developer solution
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Convert silver halide crystals into black metalic silver. Contains a solvent, reducing agent, restrainer an activator and a preservative
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Fixer solution
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Removes unchanged halide crystals leaving black metalic silver on the film along with hardeningg it to reduce scrates. Contains a fixer agent, solvent, hardener, acidifier, and preservative
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FFD
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Focal film distance = Increase of this increases detail, penumbra decreases, and an increase of it causes less distortion
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OFD
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Object film distance = Increase of this , detail is decreased, and penumbra is increased. If it's decreased, there is less distortion
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