| Question | Answer |
| 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 |
