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