Fluoroscopy Flashcards
Difference between fluoro and rads when discussing mA?
Fluoro: low mA (0-5) Rads: High mA (200-800)
Fluoro vs rads: spatial resolution
Rads are better
Fluoro vs rads: Contrast
Rads are better
Fluoro vs rads: Temporal resolution
Fluoro is better
Difference between “Spot hold” and “Last Image Hold”
Spot hold - like regular rad
Last image hold - more quantum mottle - just the last image of the fluoro image
Two types of fluoroscopic mechanism
1) Image intensifiers
2) Flat Panel Detectors
Source from above the table causes higher or low dose to technician?
Higher
Brightness gain is a combo of?
Flux gain - 50x (this stays pretty much the same and is caused by the difference between photocathode and anode) - This is how fast those fuckers are flying (electrons)
Minification gain - The image getting smaller at the out put phosphor concentrates photons
How does EM change in an image intensifier? Basically how is the x-ray signal transmitted through the system.
x-ray—-(Input phosphor) light—- (Photocathode) electrons—- Focusing electrodes (flux gain)—- (Smaller output phosphor) light
Electrons lens or Electrostatic focusing lens does what?
- Focuses the beam to a focal point (in control of electronic magnification)
- Speed up electrons
- Reserves and Inverted image
Why is the output phosphor made out of zinc-cadmium sulfide?
To keep the output phosphor thin and therefore maintain spatial res.
What are special characteristics of cesium iodide (CsI) in the input phosphor?
1) Packed tight together: more efficient at gathering electrons
2) Vertical orientation of crystal needles: Reduces lateral light diffusion
3) K-edge: more absorption
4) Thickness of CsI is also less than old ZnCdS and therefore improved spatial resolution
Conversion gain
New way to say brightness gain
What happens to conversion or brightness gain over time?
Loss of 10% over 1 year so Automatic brightness converter cranks technique and dose goes up
once 50% of previous it is time to throw away.
Spatial res for Image intensifier?
~4 Line pair/mm
What can you do if conversion gain sucks?
1) open up aperture at the cost of decreasing SNR
2) ABC increases dose
3) Replace
Brightness equation?
(D1/D2)2 = Brightness gain
(Diameter of input/diameter of output)2
As you can see making output smaller will increase you brightness, but making your input smaller you decrease you brightness
If output stays the same, but input is reduced in size.. what happens?
Minification increases
Decrease spatial resolution
Increase brightness
Having II close to patient does 3 things?
- Decrease patient dose by collecting more x-rays and not allowing ABC to increase technique
- Decrease scatter
- Increase image sharpness
Artifacts
Pincushion
S Distortion
Glare
Lag
Vignetting
Saturation
Pincushion Artifact is created by?
Peripheral electrons do not strike output phosphor where they ideally should, nor do they focus well resulting in UNEQUAL magnification
Decrease FOV
S distrotion created by?
Earth’s magnetic field having effect of electrons in I.I.
Lag artifact happens because?
Persistence of luminescence after x-ray stimulation… 1ms in I.I. but now is more associated with TVs
Vignetting is and what causes it?
Unequal magnification due to peripheral electrons not traveling where they should.. causing fall-off in brightness at the periphery.
