RDT 180 EXAM 2 11/9
scintillator:
converts xrays to light
the laser is made of
helium neon or solid state diode
what is used on screen to release any trapped electrons
high intensity bright light
the light that is released is considered our
image
AMFPI/AMA stands for
Active-Matrix flat panel imagers active matrix array can both be used
flat panel detector
Solid state detector Rigid protective housing Used in both direct and indirect capture
conversion process for indirect capture
X Ray photon absorption-Phosphor based scintillator Conversion from light to electric charge-photodetector (made of = amorphous silicon) (a-Si) Readout layer-TFT ADC conversion
conversion process for direct capture
X Ray photon absorption-photoconductor- amorphous selenium (a-Se) Conversion to electric charge- electric charge Readout layer- TFT ADC conversion
sensing and storage material: photoconductor=
a:SE
as the light is stimulating the color layer
absorbs the stimulating and reflects emitted light forward
AMFPI/AMA MEASURES
absorption NOT AMOUNT OF XRAYS
things that can cause imaging plate to have artifacts
age - areas of radiolucency static from low humidity can cause hair to stick to ip dust dirt scrcthed back scatter-can cause dark lines on image
Absorption and conversion material attached array surface is our:
ama
conversion material for indirect
amorphous silicon
what does the monochromatic red light do
applied to release electrons from f-trap
operating processing artifacts can include
backward cassette incorrect part/position insufficient collimation incorrect sampling BIII
stimulating light is
bad
phosphor/active layer is made of
barium fluoride with small amounts of europium
when the laser passes through the beam what happens
beam shaping and oscillating / rotating mirror narrow the beam keeps size shape speed and intensity constant
what is emitted when the electrons are given energy
blue and violet light
switch=
circuit device that collects electrical signal When TFT is activated/closed signal is sent to ADC computer
solve imaging plate artifcts
clean plate refer to vendors recommondations frequency of cleaning depends on usage
what does the light collecting optics/ guide do?
collects light focuses and narrows light towards optical filter filtering out stimulating light-noise
while the light is stimulating what 2 layers are working
color and reflective layer
photodetector/photodiode/photomultiplier
convert light to electrons (signal;)
digital electronics
convert signals to digital forms
photoconductor:
converts x-ray photons into electrons
how often should the plate be in erase mode
daily or once a week
ADC converts to
digital signal unique values-preprocessing any remaining energy removed with bright white light
phosphor is taking
electrons converting to light
the signal is the
emitted light
as the laser scans it gives what to the trapped electrons
energy to release them
2 things preventing artifact
felt in cassette conductive layer in plate
insufficient erase=
ghost or phantom image
low snr=
grainy image
stationary grids= MOIRE EFFECT
grid lines must run perpendicular to laser scan
ghost/phantom image
if another image was taken on top of cr plate before laser extracted image
the remnant beam (process of acquiring image) -
interacts with the electrons of the barium fluoride crystals they give energy to the electrons in the crystals trapping them in the phosphor center-LATENT IMAGE signal remain for hours-loses intensity till process
what is slow scan
ip is moved slowly along axis-beam constant plate moving up
fast scan is
laser moved across ip in raster pattern left to right horizontal
sensitivity center where electrons are trapped and stored is
latent image in the phosphor active layer
the photodetector takes
light converting it to an electrical signal in adc
the cassette is made of
lightweight plastic material lead back felt
our readers stimulates with what type of laser
monochromatic red light
greater the sampling frequency
more info collected
laser is a
narrow intense beam of light
on the plate reader why would white leans appear
parallel lines caused by dirt dust or scratched on light guide or collection mirror
where is the late image stored
phosphor active layer
absorbing material for indirect
phosphor based scintillator
the emitted light is sent to the
photo detector
photo detector is also the
photo multipler photo diode
absorbing and converting material for direct
photoconductor (amorphous selenium)
computed radiography is comprised of
photostimuable storage phosphor cr reader digital electronics
process stimulating the phosphor and releasing light
photostimulable luminescence PBL
readout of our image
placed in reader immediately plate removed inside
artifacts include
plate reader imaging plater printer image processing PIPI
most is tased during
process when electrons return to low energy state
what will improve signal to noise ratio in the psp plate process
proper filtering
cr imaging plate layers
protective layer phosphor/ active layer reflective layer conductive layer color/light shielding layer support layer backing layer
the felt in the cassette is useful because
protects against static electricity, dust nd mechanical damage
backing layer
protects back
reflective layer
reflects light sends light in forward direction to reduce stimulating light and escape of emitted light loss of detail
measure of the true signal
represents actual anatomy to amount of noise prpesent
grid selection and collimation is
same as screen film more important-sensitive to scatter ratio focus grids
coherent light
same frequency traveling in same direction
the electrical signal is :
sampled and digitized assigned a value to each light photon to represent location in matrix and brightness
how many pixels per mm the laser scans with each line
sampling frequency
rate at which the laser extracts the image data from the plate
sampling frequency
the cr plate is sensitive to
scatter
support layer
semi-rigid strength support layers
as the light is stimulating the reflective layer
sending emitted light in forward directing
storage
should not be stored n temp over 95 no direct sunlight rough handling dropping can cause cracking
readers can be
single or multiloaders
correct cassette is chosen by
size and type standard or high resolution plate
high resolution plates are
small cassette extremityi thinner phosphor small pixel size
the more signal sampled
smaller the pixels
each del contains:
storage capacitor, thin film translator (switch) and pixel detector
capacitor=
stores electrons and measures charge
light emitted is proportional to
the absorbed radiation
the absorbing material depends on:
the conversion direct or indirect
emitted light is
the image good
the more radiation absorbed
the more light emitted
the barcode or id window indicates
the orientation of the plate when taking an xray to display it correctly on the monitor
protective layer=
thin clear plastic protects phosphor
TFT AND FET stand for:
thin film transistor switch field effect transistor switch used interchangeably
to increase spatial resolution we must increase
thinner phosphor layer bigger crystals translation speed smaller diameter laser beam increase sampling frequency pixel size
photostimuable storage phosphor
to acquire xray projection
cr reader
to extract the electronic latent image
slow scan is also
translation subscan
crystals in the phosphor=
turbid
the barcode / id window is a
unique code to match image with patient scanned under correct cord so apr is processed correctly
indirect=
x ray photons -> light -> electrical charge/signal Scintillator-phosphor and photodiode/photodetector
direct=
x ray photons->electric charge/signal Photoconductor-no phosphor/scintillator
sensing and storage material; photodiode=
a:SI
what does dye n the phosphor active layer dp
absorb stimulating light preventing spread
the pixel detector is considered the:
absorbing/converting material
conductive layer
absorbs and reduces static electricity
color/light shielding layer
absorbs stimulating lights and reflects emitted light
pixels in our ama are called
DEL detector elements
amfpi/ama:
Flat panel array with an x ray absorption material array of pixels