dynamic image recording (fluro) Flashcards
what is fluoroscopy?
real time ‘dynamic’ x-ray images
who was fluoroscopy invented by?
thomas edison
when does luminescence occur?
occurs when materials absorb energy and emit light
two categories of luminescence
- fluorescence - light emitted very quickly
- phosphorescence - light emitted more slowly
when in radiography is fluoroscopy used?
when images should be sharp
what type of imaging does fluoroscopy use?
continuous ‘real time’ imaging
- low continuous x-ray exposures (0.5mA - 2mA)
what is fluorography
can select on machine the function to give a still image with HIGH resolution
image intensifiers
older way of obtaining fluoroscopy and fluorography
pros of image intensifiers
reduces patient dose by amplifying image signal
cons of image intensifiers
- image noise
- loss of sharp image
- image distortions
what is image noise
- signal that comes from anything apart form anatomy of patient
- noise present in all electronic systems
- appears as irregular granular pattern
examples of general fluoro procedures
- gastrointestinal studies
- angiography of vessels
- micturating cystograms
- proctograms
- HSG
examples of interventional fluoroscopy procedures
- angioplasty
- stenting
- embolization
- biopsy
- drainage
how does an image intensifier work in a fluoroscopic chain
Electronic vacuum
- convents remnant beam —> light
- light —> electrons
- electrons —> back to light
- increases light intensity in the process
5 components of fluoroscopic chain
- x-ray tube
- collimators
- filtration
- patient table
- anti-scatter grid
what is the patient table made up of and why
carbon fibre
- strong enough to hold patient with minimal radiation absorption
where is the image intensifier position
the intensifier usually above table
what does an image intensifier include?
- input phosphor and photocathode
- electrostatic focusing lens
- accelerating anode
- output phosphor
how much kV to accelerate electrons in image intensifier
25-35 kV
what does an input phosphor do?
converts x-ray photons to (blue) light photons
what is an input phosphor made of
fine caesium iodide crystals (CsI) - high X-ray absorption rate
what does thicker layers help achieve
improved efficiency - 60% of X-ray energy converted to light
what does a photocathode do
converts blue light photon energy to energy possessed by released electrons
why is the photocathode curved
so that all electrons travel the same distance to output phosphor
what is a photocathode made of
made of Sb.Cs (antimony and caesium)
what is the purpose of negatively charged focusing electrodes
repel electron stream steering them to output phosphor
what is the potential difference across the vacuum in an image intensifier
25-35kV = accelerates electrons as they pick up kinetic energy
where is the anode located in the image intensifier
at the neck - +ve charged to provide a stream of electrons at constant velocity
what does the output phosphor have a thin layer of and why
- aluminium
- prevent light travelling back to input phosphore
what is output phosphor made of
- zinc cadmium sulphide
- converts electron energy into green light
describe the process of flux gain
- converting x-ray photon energy to many light photons
- converting light photons to energy gained by electrons
- electrons emitted from cathode - accelerate + gain kE
- converts electron energy to light photons
- gives 100x increase in brightness
describe the process of minification gain
- output phosphor is smaller than input phosphor
- reduction in actual image size (minification) = same number of electrons concentrated on smaller surface area
- results in a 100x brighter image
what is the intensifiers ability to increase the brightness of image is called
flux gain x minification gain
(brightness gain or conversion factor)
what is exposure factors in fluoroscopy controlled by
ABC (automatic brightness control)
- automatically adjusts kVp + mA
- achieved by monitoring brightness of output phosphor intensity
- ensure brightness of image at monitor is constant
how to adjust magnification in an image intensifier
- achieved by increasing the voltage to focusing electrodes
- focuses down electron beam by electrostatic repulsion
- so only electrons from centre portion of photocathode interact with output phosphor
what reduces brightness
only central part of photocathode provides electrons to output phosphor
how does ABC contribute to compensate in reduce brightness
may automatically increase radiation dose
