what are artifacts? what can cause them?
any undesirable densities on the processed image other than those created by scatter or fog
damage to CR plate or DR detecter
malfunction of CR reader
tech error
phantom image
result of incomplete plate erasure
shadow of prev img on the new img
scratches
dirt/dust
permanent damage to the phosphor layer of plate, it will need to be replaced
appears as bright spots on image
dropout artifact
fog
white lines
areas of img w reduced resolution due to dust on laser reader
result of background radiation, makes img look darker
result of dust on light guide, appears as white lines parallel to direction of travel on image. reader has to get cleaned or serviced
what is used to clean CR plates? what is it known to do?
oxivar
known to leak thru edges of cassettes and damage the PSP inside
moire artifact
aka zebra patter, grid lines and direction of reader are parallel showing lines on img
aliasing
not enough analog data is converted to digi. shows lines on image like moire CR artifact
this is a sampling error
dead/dropped pixels
how is this fixed?
pixels tjat are malfunctions and dont capture xray. can misrep anatomy, is many are missing can show dark spaces or lines
can be fixed w gain calibration or flat fielding to help compensate for dropped pix
what is gain calibration or flat fielding and how does it work
algorithm used to correct flaws on decetor
uses interpolation that will assign a value to the dead pixels based on the value of those around it
image lag/ghosting
how can we prevent this?
occurs when sys can take imgs faster than they can be processed. 1st img still held on detector when 2nd img is taken
increase time between expos
collimate so theres less to prcess
use proper tech factors
what is exposure indicator number
represents the amt of rad that struck the IR. there is an accepted range and an ideal #, #s outside this range indicate the IR was overexposed or underexposed
at RRC what exposure indicators are used for DR, CR and mobile? what are the ideal values?
DR- philips EI. ideal expo is 200
CR- fuji sensitivity #. ideal S value is 200 (S # is an indicator of the PSL given off by plate when scanned)
M- phillips deviation index
whats the range for fuji
100-400
inversely proportional to expo so 400 = insufficient expo and 100= excessive expo
larger # = the more expo needs to be amplified
whats the range for phillips exposure index ? whats ideal for chest?
100-300
300= excessive expo
100= insufficent expo
ideal for chest = 450
what is used as a consistent way to indicate how much rad the IR received
deviation index
what is deviation index
a comparison between the actual expo received by IR and the proper expo it should have received
helps determine if IR was under or over exposed
what is target exposure index EI_T
what is signal-based exposure index EI_s
what reps the difference between these two?
EI_T- the ideal exposure for each projection
EI_s- calculated based on amt of expo in the region of interest (the amt you actually got)
deviation index represents the difference between EI_T and EI_s
what is the ideal DI #? what does it mean if below or above?
0 (green)
below= under expo (yellow)
above= over expo (red)
what influences exposure indicator #
kV and mAs selected
gonadal shield
poor collimation
too much anatomy in img
wrong menu selected on reader
