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Sherer Ch10

QuestionAnswer
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