week 8 Flashcards
factors affecting fluoroscopic image quality
- contrast
- noise
- sharpness
- distortion
- temporal resolution
how can image contrast be improved
- use of exogenous contrast agents
- radio-opaque makers on instruments
- high exposure rates
how can noise be improved
using higher frame rate
what is sharpness influenced by in II
- display matrix
- focal spot size
- image noise
- motion
- FOV (or geometric magnification)
what is sharpness in FPD dependent on
- display matrix
- focal spot size
- image noise
- motion
- pixel size of receptor
types of image distortion/ artifacts in a cathode ray tube (CRT) TV monitor (Vidicon/Plumbicon)
- veiling glare
- vignetting
- blooming
- pincushion distortion
- S distortion
daily QC by the radiographers
- visual check
- functional checks - fluoroscopic unit and other accessories equipment
weekly routine QC check by radiographers
- top up consumables
- cleanliness of the storage compartment
- storage devices load
- removal of stored data to clear the worklist on equipment
2 non vascular interventional radiology procedures
- biopsy
- FNAC and Tru Cut Core - Drainages
risk of FNAC
seeding tumours
patient preparation for drainages
- fasting for at least 6 hours
history of fluoro
- Whilhelm Conrad Roentgen
- 8 nov 1895
primary function of fluoro
- live display anatomy
- dynamic motion/ process
- interventional procedures
oldest device used for fluoroscopy
cryptoscope
effective dose of a barium enema procedure
3-6mSv
xray vs fluoro
xray
- high mA, low second
- high SNR
- low temporal resolution
fluoro
- low mA, variable second
- low SNR
- high temporal resolution
how does frame averaging affect image quality
frame averaging = decrease noise = decrease temporal resolution
components of a conventional fluoroscopic unit
- high voltage generator
- xray tube
- xray image receiver: II
- viewing system
undercouch fluoroscopy meant that detector is
on top
components of the II
- input phosphor layer
- photocathode
- focusing electrode
- vacuum enclosure
- anode
- output phosphor layer
what does the input phosphor layer consist of
cesium iodide (CsI) crystals
- prevent lateral light spread
- for scintillation
what is the function of the photocathode
- converts light photon to photoelectron
- efficiency 20%
what is the output phosphor layer made of
thin powdered phosphor
what does the output phosphor layer do
converts photoelectron back to light photon
how many electron corresponds to how many light photons
1 electron = 200 light photons
what is the formula for brightness gain
minification gain x electronic gain
how is geometric magnification achieved
selecting smaller central portion of the input phosphor to project onto the output phosphor
what does magnified image compromise
noise becomes more prominent –> reduced SNR
- solution is to increase air kerma = increase radiation dose
what is automatic brightness control for
to prevent fluctuation in
- brightness image
- SNR
major component in an optical system
- collimating lens
- aperture
- focusing lens
what is the function of the optics camera system
captures and converts light photons to analogue electrical signals
what in the conventional fluoroscopic system is combined to form a FPD
- II
- optical lens
- camera
- analog processing & A/D
- video camera
- cine camera
pros of II
- better low noise performance
cons of II
- big and bulky
- risk of image distortions
pros of FPD
- less bulky
- absence of image distortions
- broaden applications
cons for FPD
- high electronic noise at “low noise level range” compared to II
