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Question Answer
What does Cr and dr stand for ? Cr = computed radiography. Dr = digital radiography
What is analog data Continuous data . Ie. Image in monitor – many shades of grey
What is digital data Finite. Numerical representation of analog data . Ie. Each shade of grey assigned a number
What is ADC Analog to digital converter.
What is DAC Digital to analog converter
What is dynamic range Ability of an imaging system to respond to varying levels of exposure
What is latitude Amount of error that can be made in exposure factor choice and still result in capture of quality image
What happens in conventional radiography Transmit rad creates latent image on film. Film is chemically processed to reveal image. Image is viewed on box.
What is Cr process Exposure. X rays interact with photostimulable phosphor.PSP scanned by red laser. PS P emits blue light (image). PSP is erased
What is primary function of cassette Protect imaging plate . Blue or green lines
Cassette has a what label to help match exam with correct patient Barcode
Where is photostimulable imaging plate placed Inside a cassette
What is PSP composed of Europium activated barium fluorohalide
Latent image on phosphor coated plate where image is stored remains for up to ? 24 hours
How long until the image starts to degrade 8 hours
What are the layers of the psp From top to bottom: protective layer. Phosphor layer . Light reflective layer. Conductive layer. Support layer . Light shielding layer. Backing layer. Barcode
What is the key ingredient of psp Barium fluorohalide with europium
How are latent images represented X rays interact with PSP causing outer shell electrons to be in an excited state . The electrons are held there, they represent the image
Barium has high or low k shell binding energies ? Low
Is PSP sensitive to scatter radiation? Yes because of barium low k shell binding energy
What does PSP stand for Photostimulable phosphor
What does pmt stand for Photomultiplier tube
What is step one in Cr process Plate is exposed to radiation in a normal manner. Electrons in the phosphor are excited to a higher energy state. Some electrons are trapped in holes. The trapped electrons hold the image
What is step 2 in Cr process Plate is put into reader and is scanned by red laser beam . The trapped electrons absorb the laser light energy , which allows the electrons to be freed
What releases blue light as it is scanned ? pSP
What is step 3 in Cr process When electrons return to the lower energy state , they emit a blue/green light . The fluorescence is collected by a photomultiplier tube . The pmt detects the blue light , aomlifies it and sends it to be digitized.
What does the pmt do Collects light and converts it into electrons
What is step 4 in Cr process
As the plate is being read, most electrons will return to their ground state . Once the plate is read it is flooded with a bright white light. This will erase the image and return any remaining electrons to ground state
In order for output signal of pmt to be manipulated by the computer it much be converted into what A digital signal (ADC)
What is ADC Converting digital signal into analog
What is DAC Converting digital signal into analog
In the Cr reader the laser beam passes through what Beam shaping optics to an optical mirror
What does the mirror do? Directs the laser beam to the imaging plate
What shapes the laser beam so that it is the same size, shape and speed regardless of where on the plate it is pointed Special optics
What scans the imaging plate in a motion that is perpendicular to the direction that it is moving The laser beam
What is translation The movement of the imaging plate through the Cr reader as it is being read
What does reading the image do to the electrons Returns electrons to lower energy state
What are very sensitive to background radiation cR plates
When do you use the erase cycle in reader At least every 48 hours to remove scatter from plates
What is structured needle phosphor Needle shaped phosphor crystals (cesium iodide ) have improved radiation absorption efficiency
How is the structured needle phosphor orientated 90 degrees to the screen surface for reduced light spread
What are more uniform sensitive later than powder phosphor Structured needle phosphors
Control of light spread causes ? Increased sharpness
What does dual side IP allow ? The use of a thicker phosphor layer on the IP and transparent base, thereby increasing detective quantum efficiency
How does dual side imaging plates increase detective quantum efficiency? By collecting the emissions from both sides of the IP with optimal , spatial frequency dependent factors
What are some possible plate artifacts Ghost images . Scratches. Dust/dirt . White lines . Droupout fig
What are ghost images Incomplete plate erasure
What are scratches Permanent dmaage to the phosphor layer of the plate
Dust will appear as? Bright spots on image
What is due to the dust on the light guide White lines
What are droupout artifacts Areas of image that with reduced resolution
What is fog Results from background radiation. Will give image a darker appearance
What do you do if image appears to be in diagnostic due to exposure factors Density and contrast can be adjusted by post processing
What are exposure indicators for cr Fuji. Afga. Carestream.
What does film world = Dose and image density are closely related
What does digital world = Signal to noise ratio
What can images be given in order to achieve the same image brightness Half or two times the dose
What varies in dose considerations The amount of noise
What is the exposure indicator number Represents the amount of light given off as the IP is read
What is an indicator of amount of radiation absorbed by the psp Exposure indicator number

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