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swtjo3joe
on FreezingBlue Flashcards.
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Utilizing 120 secs for an upper GI exam will deliver how much skin entrance exposure?
5-15 rads
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the skin entrance dose for an AP abdomen is?
100-500 mrads
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how thick should filtration be when 125-150 kVp is used?
3 mm aluminum
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what happens to patient dose when the patient-to-image intensifier increases?
- increases
- because fewer x-rays are intercepted at the image intensifier due to inverse square law losses
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what type of exposure switch do fluorscopy machines have?
dead-man type
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the image intensifier is of what type of protective barrier?
primary
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how thick do protective curtains have to be?
0.25 mm lead
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are protective curtains required for c-arms?
no
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scatter radiation from the patient at one foot from the patient produces how much radiation?
as high as 500 millirads per hour
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the predetermined time limit may not exceed how many minutes?
5
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what does the input phosphor do?
absorbs x-rays and converts their energy into light
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what does the photocathode do?
converts light into electrons
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what does the accelerating anode do?
speeds up the electrons from the photocathode
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what do the electrostatic lenses do?
focus the electrons onto the output phosphor
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what does the output phosphor do?
converts electrons into light
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what is brightness gain?
flux gain x minification gain
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what is flux or electronic gain?
acceleration of the electrons
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what is minification gain?
minification of the output phosphor (output phosphor is smaller than the input phosphor)
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what are the two types of contrast in fluoroscopy?
- subject (controlled by kVp)
- detector (characteristics of the II, type of TV camera target, amplitude of the output image brightness/video signal, and brightness/contrast settings of the monitor)
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how is resolution measured?
in line pairs per millimeter (lp/mm)
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the overall resolution of an imaging system is expressed in terms of its what
modulation transfer function (MTF)
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what is pincushion distortion?
when the input screen, which is convex, does not completely eliminate edge distortion at the output screen
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what is vignetting?
- a fall-off in brightness at the periphery of an image
- because the peripheral image is displayed over a larger area of the output screen, thus its brightness gain is less than that in the center
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what part of the II is responsible for magnification?
- focusing lenses
- change in voltage to focusing lenses changes standard to mag mode
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how does image magnification work?
- proportional increase of voltage to the focusing lenses further compresses the electron beam
- results in a smaller input surface and image mag
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what type of camera is usually used in diagnostic fluoroscopy?
vidicon camera
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what is in a vidicon camera?
- vidicon tube
- small electric vacuum (photoconductive target)
- electron gun
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how much does the image intensifier amplify the image brightness by from the original?
about 10,000 times
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what type of fluorescent material are made up of in early fluorescent screens?
barium platinocyanide
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what type of fluorescent material replaced the old type of fluorescent screens?
cadmium tungstate then zinc-cadmium sulfide
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what was the main drawback of fluorscent screens?
because of the deficiencies of the human eye at low light levels
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what eventually replaced fluorescent screens?
image intensifier devices
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early image intensifiers consisted of what materials?
- system of optical lenses
- mirrors
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what was the major problem with the early image intensifiers made up of optical lenses and mirrors?
- the viewing angle was narrow
- only one person can view the image at a time
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what type of system/object replaced the early image intensifier system to negate the narrow viewing angle?
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the input layer is made up of what four components?
- input window
- substrate
- input phosphor
- photocathode
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a potential radiation dose of 100 mrems to a surrounding is called what kind of an area?
high radiation area
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a potential radiation dose of 5 mrems to a surrounding is called what kind of an area?
radiation area
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