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Fluroscopy Darcie

Flouroscopy Darcie

QuestionAnswer
what is the purpose of fluoroscopy to image objects in motion(dynamic imaging)
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
who invented first fluoroscope?, when? Thomas Edison, in 1896
what is brightness gain the increase in image intesity, caculated by minification gain x flux gain
minification gain input phosphor diameter divided by ouput phosphor diameter squared
flux gain ratio of output phosphor light photons to input phosphor light photons (OP/IP)
conversion factor luminance of output phosphor divided by exposure rate of input phosphor (sometimes used instead of brightness gain)
-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)
what is the weakest link in the entire fluoro system tv chain
tv monitor allows for us to manually or electronically control density and contrast if needed
veiling glare reduction in contrast due to internal scattered radiation, scattered electrons or scattered light
lag continued emission of light when turned off
vignetting loss of brightness at periphery
pincushion effect loss of sharpness at periphery due to curve of IP screen
S distortion in presence of electromagnetic field -image sharpest and brightest at center
video camera control system quicker response as no change in technical factors
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
cassette spot films only advantage is larger image -more radiation
spot film resolution is dependant upon what -5 geometric factors -minification gain -electrostatic focussing point -IP,OP diameter -viewing system -OID -Phosphor size/thickness
quantum mottle is controlled with which technical factor mA
what is a fluoroscopic screen zinc cadmium sulfide hand-held then attached to table(Dark Fluoroscopy)
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
when was image intensified fluoro developed -1948 -uses 2 phoshpors *input(cesium iodide) *output(zinc cadmium sulfide)
scotopic vision -uses rods -night vision -less visual acuity
photopic vision -uses cones -daylight -better visual acuity
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
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
image intensifiers -use cone vision(photopic) -increased visual acuity(x10) -amplifies brightness 500-8000 times -tube is glass or metal vacum
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
photocathode -photoemissive cesium and antimony applied onto a protective coat -converts light into electrons
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
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
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
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
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
video camera tubes -vidicon or plumbicon
vidicon/plumbicon cathode -cathode end has heating element that forms electron gun as it thermonically emits electrons
vidicon/plumbicon control grid sits around electron gun and forms electrons into a beam, accelerated toward target by potential difference(accelerator grids)
vicicon/plumbicon anode and wire mesh decelerates beam and allows for it to strike target perpendicularly
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)
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
vidicon/plumbicon signal plate -made of thin positively charged graphite -conducts video signal out of the tube into external video circuit
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
to allow for spot films video camera tubes use what beam splitter
tv or computer matrix system -electronically controls brightness and contrast -multiple viewers
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
Created by: bigad1982