fluoroscopy Flashcards
what is fluoroscopy used for?
to visualise motion, x-ray in real time
continuous _ _ exposure is needed for fluoroscopy
continuous low dose exposure is needed for fluoroscopy
what is required due to the use of low dose exposure in fluoroscopy?
an image intensifier
what is the goal of the image intensifier
to brighten the image
name three components of the image intensifier
input phosphor, photocathode, output phosphor
what does the photocathode do?
converts light to photoelectrons
what is inputted into the input phosphor?
x-rays
what % of x-ray input is absorbed by the input phosphor and why?
60% of incoming x-rays are absorbed by the input phosphor, this is due to the k-edge effect
what happens to the photoelectrons after the photocathode?
they are accelerated across the tube by a high voltage (25kV) towards the output phosphor
the image produced by fluoroscopy is
1.
2.
3.
the image produced by fluoroscopy is:
1. inverted
2. reversed
3. minified
where is the lowest efficiency in the II?
At the input phosphor
what is the intensification factor
the intensification factor is a measure of the increase in light output compared with the light produced at the input phosphor
what two factors influence the intensification factor?
the minification gain and the flux gain
flux gain formula?
electrons from output phosphor
/
#electrons from input phosphor
minification gain formula?
diameter of the input phosphor
/
diameter of the output phosphor
what is the reasoning behind the pincushion effect?
distortion of the image due to the divergence of the peripheral electrons at the output phosphor, leading to unequal magnification
what is vignetting?
this is where the centre of the image is brighter than the peripheral, also due to diverging peripheral electrons
what detects the light from the output phosphor?
charge coupled device (CCD) detects the light from the output phosphor
what does modern fluoroscopy use instead of the image intensifier
modern fluoro units use a flat panel image receptor
what does magnification improve in II fluoroscopy, but not in digital fluroscopy?
magnification improves spatial resolution in older fluoroscopy units, but does not improve spatial resolution in digital fluoroscopy.
advantages of digital fluoroscopy?
no distortion, unaffected by magnetic fields, wide dynamic range, improved contrast.
