121 Unit 1
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| ma determines | tube current
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| current in units | amperes
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| mas and density | mas is directly proportional to density
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| time in seconds | how long it takes electrons to get to anode
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| kvp | penetrating power, force applied to push the e from cathode to anode;controls QUALITY
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| % to notice change in density | 30%
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| law of reciprocity | density should remain unchanged as long as the intensity and duration remain unchanged
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| relationship between mas and dose | directly proportional
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| relationship between kvp and dose | direct relationship
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| s# and density | inversely related; high s# underexposed, vica versa
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| inverse square law | inverse relationship between distance and dose; half the sid, 4x the exposure
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| maintaining density using kvp and mas | decrease kvp 15% and double mas
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| tool measuring optical density | densitometer
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| step wedge | penitrometer, shows gray scale on film
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| step wedge, more steps | long scale, increased kvp, decreased contrast
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| 4 radiographic properties | density contrast recorded detail and distortion
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| 4 prime technical factors | ma time kv and distance
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| geometric variables | sharpness -> (radiographic)detail and distortion
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| photographic variables | visibility (of detail) -> density and contrast
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| density | overall darkness of film, dependant on amount of exposure, must have adequate density to evaluate other qualities
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| contrast | presence or absence of shades of gray
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| more exposure | black areas, opaque
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| less exposure | white areas, translucent
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| film translucence | caused by radiopaque object
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| film density | is dependant on the # of exposed silver halide crystals
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| crystals in processor | turn into black metallic silver upon development; more crystals faster film
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| latent image | before processing
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| manifest image | after processing
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| useful range of density | .25-2.0
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| mas and quantity | ma, # of photons produced, aka output, intensity, exposure
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| quality | kvp, penetrating ability of beam
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| Milliamperage | # of electrons crossing the tube from cathode to anode per second
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| relationship between ma and density/tube current | directly proportional
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| kvp and density | kvp has the greatest effect on density, but is not used to control density
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| 15% rule | increase kvp by 15% doubles density and vica versa
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| kvp and contrast | inverse relationship
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| to decrease contrast and maintain density | increase kvp by 15% and halve mas
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| sid | aka FFD, focal spot to film distance
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| inverse square law | intensity of radiation varies inversly with the square of the source
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| mas distance formula | to compensate for density changes with changes in sid
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| rule of thumb for sid and intensity | doubling the sid gives 1/4 the intensity, use 4x the mas; 1/2 the sid gives 4x the intensity therefore use 1/4 the mas
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| double kvp | density will increase by a factor of 4,5, or 6
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| changes in kvp; 30-50 kvp | 5% change in kvp
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| changes in kvp; 50-90 kvp | 8% change in kvp
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| changes in kvp; 90-130 kvp | 10% change in kvp
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| aec | 1942, determines exposure time and therefore the total mas; must still set kvp, chambers and density selection
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| density selections | only way to increase or decrease density using aec; increments of -1,-2,0,+1, ect
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| phototime | didn't have ionizing chambers, only IR, flourescent screen, and photoiodide
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| fog and density | direct relationship
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| grids and density | increase grid ratio, decrease density, inverse relationship
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| screen speed and density | direct relationship
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| filtration and density | inverse relationship
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| beam restriction and density | inverse relationship
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| processing time/temp | direct relationship
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| power supply(phase) and density | direct relationship
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| patient size and density | inverse relationship
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| factors that do not effect density | motion, focal spot size, and misaligned beam
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| anode heel effect | variation in intensity of photons across longitudinal axis of beam; need more photons for thicker body part, put cathode over that part
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| anode heel effect more pronounced | with large film size and shorter sid
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| OID | aka air gap
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| oid and density | inverse relationship b/c scatter photons diverge and miss film
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| scatter and density | direct relationship
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| density and over/under development(film) | direct relationship, overdeveloped causes increase in density
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| 5 major tissue groups | aerated, fatty, water (muscle, glands), bone, teeth; from least to most dense
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| destructive pathologies and density | degrease attenuation, density increases
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| additive pathologies | increase attenuation, density decreases and requires an increase in exp. factors
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| mAs def. | the product of tube current and exposure time
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| kvp doubled | increases amount of photons 4X
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| kvp and quality | increasing the kvp increases the speed and energy of e
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| kvp and quantity | as kvp increases more interactions occur at the target
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| tissue density and IR/film density | inverse relationship
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| radioluscent contrast (air) and density | increases density
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| radiopaquse constrast media | decreases density
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| attenuation | reduction in the # of xray photons in the beam, and subsequent loss of energy, as the beam passes through matter
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| attenuation and density | inverse relationship
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| min. mas change to change density | 30%
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Created by:
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