Exam 2 Flashcards
what is the phosphor layer made up of in a CR image plate?
barium fluorohalide
what does the conductive layer in the CR image plate do?
eliminates the electrostatic problems
what are the imaging plate layers from top to bottom?
protective layer
barium fluorohalide phosphor layer
reflective layer
conductive layer
polyester bas support layer
light shielding layer
backing layer
what causes white lines to appear on the image parallel in the direction of the imaging plate?
dust, debris, or scratches on the light guide
what is it called when the white border is eliminated during post processing?
shuttering
this light is given off when the electrons move from a high energy state to the lower energy state
photostimulated luminescence
you should always change the patient into a hospital gown
true or false
true
what is the purpose of the photodetector?
to amplify the light and send it to the ADC
how are residual images left on the image plate erased?
by flooding the plate with intense white light (fluorescent bulbs) and it pushes all the electrons in that higher energy state down into the ground state
does direct or indirect imaging use a scintillator? and what is the scintillator made of?
indirect
gadolinium oxysulfide or cesium iodide
does direct or indirect imaging use a photoconductor? and what is the photoconductor made of?
direct
amorphous selenium
what does a photoconductor do?
converts x-ray photons directly into an electrical signal
in the location domain what is needed to achieve better spatial resolution?
more pixels and smaller pixels
in the frequency domain what is needed to achieve better spatial resolution?
more lines per mm
isolates each pixel element, stores charges, acts as a switch to send electrical charges to the ADC and then the computer
thin film transistor (TFT)
what is quantum model?
image noise, image is underexposed, means in needs for x-ray photons
more lateral light spread =
worse spatial resolution
what has crystals that are amorphous shapes the spread/refract light?
gallium oxysulfide
what is more tubular/straw like and doesn’t cause a lot of lateral light spread?
cesium iodide
which has results in better spatial resolution, gallium oxysulfide or cesium iodide?
cesium iodide
what is the source of stimulating light?
the laser
what uses a photodiode and what is it made of?
indirect
amorphous silicon
what does a capacitor do?
holds charges
what are the 3 main components in the active matrix array in a pixel? (flat panel detector)
TFT, capacitor, sensing area
increased sensing area =
increased fill factor
digital image contrast is not completely dependent on kVp
true or false
true
artifact reduction process that corrects for flow in the detector
gain calibration
what is DQE?
the efficiency of the detector to convert an x-ray signal into a useful image signal
how do you make up for a low DQE?
putting more x-ray photons into the system
increased DQE =
decreased patient dose
decreased DQE =
increased patient dose
x-ray photons interact with the scintillator and light is emitted and it goes through fiber optics or lenses and mirrors to hit the ___
charge-coupled device (CCD)
noise created by the lack of light photons from the scintillator
statistical noise
the CCD chip operates without radiation stimulation, affected by temperature, cooler temperatures are better (less noise)
dark current noise
the process of manufacturing each CCD chip is complicated and the response of each chip will vary across the array
amplification noise
what size are typical CCD chips?
2-4 cm
what is the insulator CCD layer made of?
silicon dioxide
a solid chemical element or compound that conducts electricity under some conditions which makes it a good medium for control of electrical current
semiconductor
Uses a scintillator, that when struck with x-
ray photons, converts x-rays into light
photons and stores them in capacitors.
Each pixel or detector element has its own
amplifier, which is switch off and on by
circuitry within the pixel, converting the
light photons into electrical charges
Complimentary Metal Oxide Semiconductor
Systems (CMOS)
