Fluoro Physics
Fluoroscopy
Basically many shitty radiographs with smaller radiation dose played together
ABC
automatic brightness control, with the detector, under the grid
Differences from radiography
smaller focal spot (0.3-1.2 mm)
much less heating because use in pulse mode rather than a continuous beam of radiation
Pulsed beam (7.5-15 pps or fps)
Low tube current
<1 to 10 mA (low mA)
This is why the image is shitty
About 1%% of the dose as a normal XR
Image intensifier (same as detector for fluoro)
CsI
Takes XR in —> hits CsI —> puts out light —> hits a cathode —> turns into low energy electrons —> pass through a current which makes electrons move faster through the intensifier —-> hits output phospher —> electrons converted back to light —> light goes to a camera
cannot go from original light because it is too faint and would have to give deadly amounts of radiation to get same dose as if you were to just amplify it as here
How is light amplified
flux gain
moves along electric field to make it gain energy
multiplies it about 100x
Flux gain ~50
Basically if you were to point a flashlight at a wall it would vaguely light up the wall but if you start walking closer to the wall it will have a smaller area that is brighter even though the flashlight is still putting out the same amount of power
Takes small amount of light and amplifies it about 5000x
Display monitor
Basically image has too much data to put on screen at once so came up with ways to get around that
<30 Hz interlaced
Put image up and then update every other line
lowest frame rate that avoids flicker
<60 Hz progressive
Collimation
Lower dose to patient
Less scatter
Improves image quality
Temporal filter (recursive frame average)
Taking a few frames that were already taken and averaging them together
Decreases noise
Improves signal to noise ratio by the square root of the number of frames
If recursive filtering averages 4 frames the signal to noise ratio increases by 2X
Worsens temporal resolution (worsened motion artifact)
Decreasing recursive filtering improves temporal resolution and vice versa
Want high temporal resolution = means less motion blur
Monitor
refreshes images every 33 ms
at 30 image will be shown once on screen before next refresh
at 15 pps then monitor will refresh every 2 images you take
each acquired frame shown twice on the screen
if it was 7.5 then 4x and so on
Contrast media
want 75 kV when able
Barium meal
110 kV (higher than iodine level), allows you to see through bowel a bit, not just whited out
This is above the k-edge on purpose
Acquisition (exposure) Photospot
lower noise than spot frame image
larger focal spot and smaller pixel size vs spot
10 spot images = 1 min fluoro
Cine
8-15x fluoro dose
larger focal spot
Fluoroscopy Lecture 5 - Fluoro lecture 1 - Thislecture discusses analog systems
Each dose is about 1/100th the receptor dose of a regular radiograph
Comes with tradeoff of increased noise
ABC = Automatic brightness control
Grid is used
Differences compared to radiography
Can use smaller focal spots
Beam is pulsed (not continuous I guess) = pps or fps, same shit
7.5-15 fps is typical
Tube current = <1-10 mA (low vs XR)
Image intensifier
CsI scintillator
This basically takes in the XR and small amount of light and amplifies the light by 5000x and makes it bright so we can see shit, otherwise you’d have to give crazy radiation to see stuff because its so dark
Takes in XR and makes it light basically
Light hits the photocathode
We basically bottle neck the photons to a small area and it hits a photophospher which give
Minification gain = bottle neck to a small area so the light is more focused
Flux gain = the gradient we make to force the photons (or whatever particle) to float to the bottlenecked area
Once the light comes out of the output phospher (the thing which absorbs photons and puts out the light)
We now collect that light and put it to the monitor and you have an image
ABC
Monitors how much light comes out from the output phospher
It knows how much light we need to see shit
If the image is too dark or bright it will adjust by playing with mA & kV so that the brightness is good
Similar to the AEC, but will how dark or bright it is
Display monitor
Interlaced vs progressive monitors
Progressive = shows 60 fps with a new image every 1/60th of a second (60 Hz) = better
Interlaced = new image every 1/30th of a second, basically does every line to trick your eye rather than the progressive which does every line - get weird overlap artifact
Last image hold
Shows the last frame you took, used to be that you could only see it while you are on the pedal dosing the pt
Loop hold is the same thing but for the cine
Collimation
Virtual collimation is when it shows you where the borders would be on last image hold so you dont have to fluoro to see what you are collimating
Improves image quality
Decreases scatter
Increases
Post image processing is done on a smaller area so is more efficient
Temporal filter (Recursive frame average)
Averages the frame you are currently fluoring + a few priors averaged together
This decreases noise = better signal to noise ratio
If you decreases temporal filter = faster to get image
Because if you have less images then it is easier to do? idk
If 4 frames averaged the SNR ratio increases 2X idk why some math shit
Refresh shit
30 Hz is basically 30 pps
Fluoro systems
Spacer cone = makes you have the pateint a set distance away from the focal spot because dose increases significantly there and dont want too much focally
75 kV is used typically
110 kV for barium shit
Above the k edge so that the barium itself is not too bright and then cannot see shit
Acquisitions (exposures)
Larger focal spot
Smaller pixel size
1 min of fluoror is ~ 10 exposures in terms of dose
Less noise vs fluoro (similar to radiograph)
Cine
8-15x fluoro dose
large focal spot
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Fluoro Physics