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Sherer Ch10
| Question | Answer |
|---|---|
| required to protect the patient and the imaging personnel from off-focus, or leakage, radiation by restricting the emission of x-rays to the primary beam | diagnostic tube protective housing |
| those x-rays emitted through the x-ray port tube window | useful or primary beam |
| maximum leakage radiation regulation | not to exceed 100 mR/hr when the tube operated at its highest voltage, and measured at 1m |
| what type of material routinely used in manufacturing of x-ray table? | carbon fiber |
| accuracy of SID measurement | within 2% of the indicated SID |
| most popular & versatile x-ray limitation device | collimator |
| all the radiation that arises from the interaction of an x-ray beam with the atoms of a patient or any other object in the path of the beam | scattered radiation |
| x-rays emitted from parts of the tube other than the focal spot | off focus, or stem radiation |
| why can stem radiation never be totally eliminated? | because lead shutters cannot be placed immediately below focal spot |
| how far away should the collimator be from the skin to prevent skin sparing | 15cm |
| scientific term referring to brightness of a surface | luminance |
| primary unit of luminance | candela per square meter (nit) |
| simplest of all beam limitation devices | aperture diaphragm |
| where are beam defining cones routinely used? | dental radiography |
| what governs the beam restriction in a cone? | lower rim or angle of flange |
| what is the purpose of beam filtration? | reduce patient absorbed dose & increase average beam energy |
| includes glass envelope, insulating oil, & glass window | inherent filtration |
| what is the aluminum equivalent of inherent filtration? | 0.5mm |
| light localizing variable aperture collimator provides how much filtration? | 1.0mm Al eq |
| usually consists of sheets of aluminum of appropriate thickness | added filtration |
| how much total filtration is neccessary in tubes operating above 70 kVp, and mobile units | 2.5mm Al eq |
| what is total filtration required for tubes operating at 50-70 kVp | 1.5mm Al eq |
| what is the total filtration required for tubes operating below 50 kVp | .5mm Al eq |
| what takes the place of glass in the window of the mammo unit? | Beryllium |
| thickness of a designated absorber required to decrease the intensity of the primary beam by 50% its initial value | Half Value Layer (HVL) |
| how often should HVL be checked? | annually, or when tube replaced or repairs made on tube housing or collimation system |
| consistency in output in radiation intensity for identical generator settings from one individual exposure to subsequent exposures | exposure reproducibility |
| what is the acceptable variance for exposure reproducibility? | 5% or less |
| consistency in output radiation intensity at selected kVp settings when settings are changed from one mA to another | exposure linearity |
| what is the most linearity can vary | 10% |
| what percentage of recorded image is a result of visible light emitted from intensifying screens in film? | 95% |
| phosphors used in rare earth screens | gadolinium, lanthanum, yttrium |
| what is the range of atomic numbers for rare earth screens? | 57-71 |
| advantages of rare earth screens | conversion more efficient (absorb 5x more than old calcium tungstate), decreased patient dose, less thermal stress on tube, increased tube life |
| what is the effect of kVp on screen speed and patient dose | as kVp increases, effective screen speed increases, and patient dose decreases |
| what are the two most important technical considerations in the amount of patient dose? | kVp & screen-film combination |
| what material is used in the front of cassettes? | carbon fiber |
| why was the use of carbon fiber in film cassettes a benefit? | it absorbs half as much radiation as other materials used, lowers patient dose, x-ray tube life extended |
| in asymmetric screens, which screen is faster? | the one furthest from the tube (the back one) |
| what is the advantage to asymmetric screens? | greater uniformity in image and decrease in patient exposure |
| what is the SSD requirements for mobile radiography? | No less than 12 inches from skin |
| why is there a limit to how close the mobile unit can be to skin | to limit the effects of the inverse square falloff of radiation intensity with distance, and lower patient dose |
| image produced by a computer representation of an anatomic information | digital image |
| what kind of retakes will not be eliminated by digital radiography | positioning errors |
| changes light to electrical signal | photomultiplier tube |
| CR is equivalent to what film screen speed? | 200 |
| why may grids be used more frequently in CR? | CR is more sensitive to scatter radiation |
| produce the greatest patient radiation exposure rate in diagnostic radiography | fluoroscopy procedures |
| benefits of image intensifier in fluoro | increased image brightness, saving time for radiologist, patient dose reduction |
| how much does image intensifier increase overall brightness? | roughly 10,000X |
| daytime (cone) vision | photopic |
| night (rod) vision | scotopic |
| what is typical mA for fluoroscopy | 1.5-2 mA |
| what is input phosphor made of? | CsI |
| what is output phosphor made of? | zinc-cadmium sulfide |
| how does magnification effect patient dose? | increases with magnification, because auto adjusts for decreased brightness |
| what can significantly reduce patient dose in fluoro | intermittent or pulse |
| typical kVp range for fluoro | 75-110 kVp |
| what are SSD requirements for fluoro tubes, both stationary and mobile? | no less than 15" in stationary, and no less than 12" in mobile |
| what is the ideal position of the image intensifier in fluoro (mobile & stationary) | as close to patients as possible |
| how should you adjust fluoro technique for children? | up to 25% decrease in kVp |
| what is minimum filtration in fluoro tube? | 2.5mm Al eq, 3.0mm in tubes with image intensifiers |
| how does filtration effect patient dose in fluoro? | dose decreases by 1/4 when Al filtration increases from 1mm to 3mm |
| what is HVL of fluoro unit? | 3-4mm Al when kVp range 80-100 |
| what should be documented for every fluoro procedure? | total fluoro time |
| what is exposure rate limitation for fluoro units? | 10 R per minute @ 12" above, in HLC units, 20R/min |
| required protective barrier thickness? | 2mm lead eq. for image intensifier unit |
| what kind of fluoro procedures produce the highest dose rate? | cine |
| frame rate fx on patient dose | higher frame rate, higher dose |
| typical cine tabletop exposure | 25 mR/frame for 6-7" mode and 15fps |
| operating mode for fluoro equipment in which exposure rates are substantially higher than those normally allowed in routine procedures, allows visualization of smaller and lower contrast objects | high-level-control fluoroscopy (HLCF |
| limitation on fluoro exposure when HLC is present | 5 R/min when not in HLC and unlimited when in HLC mode |
| estimated range of exposure for HLC mode | 20-120 R/min |
| FDA recommends note in patient's record if skin dose of what is received? | 1-2 Gy |
Created by:
jen.studer
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