Flurorscopy Flashcards
what is the input fluorescent screen consist of? (material)
cesium iodide
how many light photons would a single 25-keV incident photon typically produce?
1,500 light photons
about how much of the incident beam does the input screen absorb?
66% of the beam - producing a good conversion efficiency
what does the photocathode do with the photons that the input screen creates?
emits them into electrons
what does the input screen do w the absorbed xrays?
emits photons
what is the job of the photocathode?
absorbs photons from input screen and turns them into electrons
what is the process that happens in the photocathode called?
photoemission (similar to thermionic emission, except the stimulation is light instead of heat)
what are the electrostatic lenses?
series of charged electrodes
where are the electrostatic lenses located?
inside the glass envelope of the tube/image intensifier
how are the electrostatic lenses similar to the focusing cup in the xray tube?
the charge of the lenses accelerates & focusesthe electron stream, which carries the fluoroscopic image
where is the anode located in the image intensifier?
inside glass envelope, and immediately in front of the output screen
how much kV is the anode usually supplied w?
25 kV
why does the anode have a hole in the center of it?
to permit accelerated electrons to pass through the anode field and onto output screen
what are the electrons converted into once they strike the output screen?
green lught photons that exit the tube
what does the output screen absorb?
electrons
what is a measurement of the increase in image intensity achieved by an image intensification tube?
total brightness gain
what is the total brightness gain determinded by?
minification gain & flux gain
what occurs as a result of the same number of electrons that were produced at the large input screen being compressed into the area of the small output screen?
minification gain
what is a measurement of the increase in light photons due to the conversion efficiency of the output screen?
flux gain
what is the shape of the input screen?
concave
what is a blotchy or grainy appearance caused by insufficient radiation to create a uniform image?
quantum mottle
what is a semiconducting device capable of storing a charge from light photons striking a photosensitive surface?
charge-coupled device (CCD)
how is the video signal emitted?
in a raster scanning pattern
what is the primary advantage of CCDs?
extremely fast discharge time, which eliminates image lag
what helps CCDs prolong their life?
by operating at lower voltages
how do digital fluoroscopy units process the image?
from the image coming from the CCD by sending an analog signal through an ADC (analog-to-digital converter)
what does TFTs replace that are in nondigital fluoro systems?
they replace the image intensifier
tabletop exposure should not exceed what rate?
10 R/min
what is the minimum source-to-skin distance for mobile fluoroscopic equipment?
12” (30 cm)
what is the minimum source-to-skin distance for stationary fluoro equipment?
15” (38 cm)
what is the federal law for a timer in fluoro?
5 minute audible timer
what is the required lead shield thickness for the bucky slot cover and the drapes?
0.25 mm/Pb
