Flouroscopy Darcie
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| what is the purpose of fluoroscopy | to image objects in motion(dynamic imaging)
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| what are the ASRT practice standards, regarding fluoro | RT only performs static imaging, not diagnostic purposes
-state law supercedes ASRT
-institutional guidelines can supercede ASRT and state law
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| who invented first fluoroscope?, when? | Thomas Edison, in 1896
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| what is brightness gain | the increase in image intesity, caculated by minification gain x flux gain
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| minification gain | input phosphor diameter divided by ouput phosphor diameter squared
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| flux gain | ratio of output phosphor light photons to input phosphor light photons (OP/IP)
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| conversion factor | luminance of output phosphor divided by exposure rate of input phosphor (sometimes used instead of brightness gain)
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| -Automatic Brightness Control(ABC) -Automatic Dose Control(ADC) -Automatic Brightness Stabilization(ABS)*DF systems | automatically adjusts technique to maintain density and contrast(kVp, mA or pulse time or a combo)
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| what is the weakest link in the entire fluoro system | tv chain
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| tv monitor | allows for us to manually or electronically control density and contrast if needed
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| veiling glare | reduction in contrast due to internal scattered radiation, scattered electrons or scattered light
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| lag | continued emission of light when turned off
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| vignetting | loss of brightness at periphery
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| pincushion effect | loss of sharpness at periphery due to curve of IP screen
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| S distortion | in presence of electromagnetic field
-image sharpest and brightest at center
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| video camera control system | quicker response as no change in technical factors
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| raster pattern | interlaced lines (520 in US) that appear due to image capture on a tv monitor. (more lines=more resolution)
progressive laser scans read all data at once, instead of left to right and provide more resolution
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| cassette spot films | only advantage is larger image
-more radiation
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| spot film resolution is dependant upon what | -5 geometric factors
-minification gain
-electrostatic focussing point
-IP,OP diameter
-viewing system
-OID
-Phosphor size/thickness
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| quantum mottle is controlled with which technical factor | mA
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| what is a fluoroscopic screen | zinc cadmium sulfide hand-held then attached to table(Dark Fluoroscopy)
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| disadvantages or dark fluorscopy | -large dose from primary beam directly at radiologist -eyes need to dark adapt to use rod vission (scotopic) *15 min to adjust -must be done in darkened room
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| when was image intensified fluoro developed | -1948 -uses 2 phoshpors *input(cesium iodide) *output(zinc cadmium sulfide)
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| scotopic vision | -uses rods -night vision -less visual acuity
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| photopic vision | -uses cones -daylight -better visual acuity
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| what equipment is in an image intensified fluoro room | -c arm attatchment *overhead II *under table II -carriage -tubes(designed to operate longer at low mA
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| fluoroscopic xray tubes | -uses pulsed beam(reduces exposure) -.5-5 mA -has fixed target -minimum SSD(source to skin distance) *15"(38cm)stationary *12"(30cm)mobile c-arm
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| image intensifiers | -use cone vision(photopic) -increased visual acuity(x10) -amplifies brightness 500-8000 times -tube is glass or metal vacum
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| input phosphor | -made of cesium iodide
-packing density allows 66% absortion of incident beam, which = good conversion efficiency
-concave to match shape of envelope, which prevents distortion
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| photocathode | -photoemissive cesium and antimony applied onto a protective coat
-converts light into electrons
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| electrostatcic focussing lenses | -negatively charged electrodes plated onto the inside of the glass envelope
-accelerates and focuses electron stream
-since optically focussed the image is inverted on output phosphor
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| output phosphor | -made of zinc cadmium sulfide or optic disc
-opaque filter is placed under output phosphor to absorb isotropic light and decrease backflow to input phosphor, which would fog image
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| anode | -sits in front of output phosphor
-positively charged with 25 kv(25,000 V)
-hole in center for passage of electrons to output phosphor
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| MAG tubes | -multi, dual, tri, or quad focus varieties
-MAG increases voltage to lenses, which = increased acceleration and moves output phosphor FS closer to input side, which = 1.5-4 times magnification
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| MAG calculations | -input phosphor divided by diameter used during MAG ex. 9"/5"=1.8 MAG
-you must collimate as dose is increased
-decreases contrast
increases dose 2-4 times
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| video camera tubes | -vidicon or plumbicon
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| vidicon/plumbicon cathode | -cathode end has heating element that forms electron gun as it thermonically emits electrons
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| vidicon/plumbicon control grid | sits around electron gun and forms electrons into a beam, accelerated toward target by potential difference(accelerator grids)
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| vicicon/plumbicon anode and wire mesh | decelerates beam and allows for it to strike target perpendicularly
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| vidicon/plumbicon focussing or steering coils/deflecting coils | -used to focus beam, for resolving power
-cause beam to scan target in a raster pattern(525-1,050 scan lines)
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| vidicon/plumbicon anode end | -coupled with output phosphor of image intensifier
-light from OP passes through the window and is absorbed by the signal plate
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| vidicon/plumbicon signal plate | -made of thin positively charged graphite
-conducts video signal out of the tube into external video circuit
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| vidicon/plumbicon target | -thin insulating mica coating with globules of light sensitive photoconductive material in a matrix pattern
-vidicon target is antimony trisulfide
-plumbicon target is lead oxide
-the more illumination = more electrons = larger video signal
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| to allow for spot films video camera tubes use what | beam splitter
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| tv or computer matrix system | -electronically controls brightness and contrast
-multiple viewers
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| radiation safety measures in fluro | -intermittnt fluoro
-pulsed beam
-5 minute alarm
-cumulative timer
-deadman switch
-moile units have cord at least 6ft long
-electronically controlled collimator shutters
-pateients table top exposure is less that 10 R/min
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