Review for Fluoro Exam
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Utilizing 120 secs for an upper GI exam will deliver how much skin entrance exposure?
the skin entrance dose for an AP abdomen is?
how thick should filtration be when 125-150 kVp is used?
3 mm aluminum
what happens to patient dose when the patient-to-image intensifier increases?
- because fewer x-rays are intercepted at the image intensifier due to inverse square law losses
what type of exposure switch do fluorscopy machines have?
the image intensifier is of what type of protective barrier?
how thick do protective curtains have to be?
0.25 mm lead
are protective curtains required for c-arms?
scatter radiation from the patient at one foot from the patient produces how much radiation?
as high as 500 millirads per hour
the predetermined time limit may not exceed how many minutes?
what does the input phosphor do?
absorbs x-rays and converts their energy into light
what does the photocathode do?
converts light into electrons
what does the accelerating anode do?
speeds up the electrons from the photocathode
what do the electrostatic lenses do?
focus the electrons onto the output phosphor
what does the output phosphor do?
converts electrons into light
what is brightness gain?
flux gain x minification gain
what is flux or electronic gain?
acceleration of the electrons
what is minification gain?
minification of the output phosphor (output phosphor is smaller than the input phosphor)
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)
how is resolution measured?
in line pairs per millimeter (lp/mm)
the overall resolution of an imaging system is expressed in terms of its what
modulation transfer function (MTF)
what is pincushion distortion?
when the input screen, which is convex, does not completely eliminate edge distortion at the output screen
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
what part of the II is responsible for magnification?
- focusing lenses
- change in voltage to focusing lenses changes standard to mag mode
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
what type of camera is usually used in diagnostic fluoroscopy?
what is in a vidicon camera?
- vidicon tube
- small electric vacuum (photoconductive target)
- electron gun
how much does the image intensifier amplify the image brightness by from the original?
about 10,000 times
what type of fluorescent material are made up of in early fluorescent screens?
what type of fluorescent material replaced the old type of fluorescent screens?
cadmium tungstate then zinc-cadmium sulfide
what was the main drawback of fluorscent screens?
because of the deficiencies of the human eye at low light levels
what eventually replaced fluorescent screens?
image intensifier devices
early image intensifiers consisted of what materials?
- system of optical lenses
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
what type of system/object replaced the early image intensifier system to negate the narrow viewing angle?
the input layer is made up of what four components?
- input window
- input phosphor
a potential radiation dose of 100 mrems to a surrounding is called what kind of an area?
high radiation area
a potential radiation dose of 5 mrems to a surrounding is called what kind of an area?
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