fluoroscopy Flashcards
photospot matrix size
1024x1024, 2 bytes/pixel, 2 MB
fluoro resolution
1 lp/mm
photospot resolution
2 lp/mm
number of photons/mm2
1000 photons/mm2
usual fluoro skin dose
<500 mGy
max allowed Kair in standard fluoro
100 mGy/min
no limit for photospot or cine
non-standard fluoro can have more
fluoro mode vs % of II exposed
normal, 100%
Mag I, 50 % (2X peak skin dose because ABC maintains brighteness at output)
Mag II, 25%, 4X peak skin dose
dose from fluoro vs photospot images
1 min of fluoro (10 mGy/min) deliverrs same patient dose as 10 photosphot images (1 mGy/image)
AEC vs ABC
AEC keeps Kair at image receptor constant irrespective of xray beam area
ABC changes Kair only when electronic magnification is changed
does pulsed fluoro reduce patient dose?
only if < 30 fps
what is pulsed fluoro
tube current is on for a short perios but increased to maintain same mAs for each frame as for continuous fluoro
brightness gain
flux gain X minification gaim
~ 5000
TV display
30 fps
minification gain
area of input phosphor/output phosphor
typical fluoro kerma area product
20 Gycm2
what does output phosphor do
absorbs electrons and emits light photons
effective dose fluoro exam
4 mSv
focal spot size fluoro
0.6 mm
1.2 mm for photospot imaging
what does photocathode do?
absorbs light photons from input phosphor and emits electrons
does switching from 30fps to 15 fps reduce dose?
-only by 35% because 15 fps uses higher dose per frame
mA and power for fluoro
< 0.5 kW
3 mA
what does lens do?
accelerates electrons and focuses them to output phosphor
what is temporal filtering
frame averaging
is KAP affected by magnification?
no because Kair increases due to ABC and area is reduced (but peak skin dose affected)
what does input phosphor do?
absorbs xray and remits as photons
veiling glare
light scattering in output phosphor
fluoro kV
80 kV
resolution of II
5 lp/mm
2lp/mm with TV
tube current for photospot image
several hundred mA
what happens to entrance Kair if patient thickness increases by 3 cm?
it doubles
order of parts in II
input phosphor- photocathode- lens- output phosphor
fluoro storage requires for 1 frame
0.5 MB
Kair at image receptor
0.03 uGy/frame
3 uGy/image for photospot
why is input phosphor curved?
lets you make it thin with minimizes absorption of incident xrays
flux gain
light at input/photons at input
~50
halving input FOV for II vs flat panel detector
-would quadruple Kair for II but only double it for FPD because FPD would use binning to reduce mottle (also reduces resolution)
response of flat panel detectors
linear
how to change resolution in fluoro
play with II FOV
fluoro imaging parameters
80-100 kVp, 3 mA
fluoro power rating
0.5 kW
3 levels of dose for fluoro
50 mGy/min, 100 mGy/min, 150 mGy/min
or
10R/min in normal and 20R/min in high dose or detail mode
