CR Flashcards
IP
Imaging plate
PSL
Photostimuable luminescence
PSP
Photostimuable phosphor
SP
Storage phosphor
SPS
Storage phosphor screen
PMT
Photomultiplier tube
T/F
CR can be substituted for screen film radiography and used with any xray imaging system
True
What are the 3 steps of the CR imaging process?
Image acquisition
Image processing
Image display
Refers to xray interaction with the imaging plate, and results in the creation of a latent image
Image acquisition
Insulates from handling trauma
Protective layer
PSP in a binder
Stores meta stable electrons
Phosphor layer
Grounds the plate
Absorbs light to increase sharpness
Conductor layer
Serves as a base
Made of polyester
Support layer
Prevents light from erasing data or leaking through the back
Light shield layer
Made of lead, reduces backscatter
Backing layer
What are computed radiography cassettes sometimes referred to as?
Filmless cassettes
What is the material of the active layer (phosphor) in the cassette?
Barium Fluorobromide crystals doped with europium
BaFBr:Eu
What is the atomic numbers of BaFBr?
56, 9, 35
Lower atomic numbers allow for k-edge attenuation between 35 and 50keV energies
What is the problem with BaFBr?
Sensitive to scatter before and after exposure to the xray beam
What happens when Compton and PE interactions occur with outer shell electrons?
The electrons are sent into a metastable state
T/F
In CR, the responses to xray interaction are electrons trapped temporarily in a higher energy, metastable state, in the IR
True
What happens when electrons return to their ground state?
They release light
(Photostimuable luminescence)
*this return can be stimulated by exposing the phosphor to intense infrared light from a laser
T/F
Metastable electrons eventually return to their ground state on their own
True
What is it called when the return to the ground state is accelerated or stimulated by exposing the phosphor to intense infrared light from a laser
Photostimuable luminescence
Emission of visible light after excitation by laser light
Photostimulation
What is the process called when the Photostimuable phosphor is exposed to a light source and emits light?
Photostimuable luminescence
Mechanically stable
Electrostatically protected
Fashioned to optimize the intensity of stimulated light
Storage phosphor screens (SPS)
T/F
Screen phosphors can contain linear filaments that enhance the absorption of X-rays and limit the spread of stimulated emission
True
What happens when the xray beam exposes the PSP?
The energy transfer results in excitation of electrons into a metastable state
T/F
Approximately 50% of electrons return to their ground state immediately resulting in prompt emission of light
True
In the stimulating process of image acquisition, what determines the spatial resolution of the CR imaging system?
Laser Beam diameter
What stage of the image acquisition system is the finely focused beam of infrared light with a beam of 50-100 um (approx. 70) directed at the PSP?
Stimulate
T/F
As laser beam intensity increases, so does the intensity of the emitted signal
True
What does the laser light cause?
Metastable electrons to return to their ground state with the emission of a shorter wavelength in the blue region of the visible spectrum
The latent image is made visible (read stage)
What are the light detectors of choice for CR?
Photodiodes (PD)
How is the residual latent image removed from the IR?
The phosphor is flooded with intense white light from a bank of specially designed lamps
T/F
If residual latent image remained, ghosting could appear on subsequent use of the IR
True
T/F
The laser light used to stimulate PSP is monochromatic
Trye
What type of laser is the stimulating source of choice?
Solid state laser
Why are solid state lasers less likely to interfere with emitted light?
They produce longer wavelength light
CR reader
Drive mechanism moves the IR slowly along the long axis of the IR
Slow scan
*motor drive must be a constant speed, if not may result in banding artifacts
CR reader
During slow scan, a deflecting device deflects the laser back and forth across the short axis of the IR
Fast scan
-Source of stimulating light
-spreads as it travels to the oscillating mirror
-scans in a raster pattern
-focused by lens that keeps the beam diameter small (<100um)
Laser
-the laser beam changes size and shape as it is deflected across the IR
-the beam is shaped by optics that keep the beam size, shape, and speed largely independent of the beam position
Beam shaping optics
Keeps the beam size, shape, speed, intensity constant
Special beam shaping optics
T/F
Laser beam diameter is critical for ensuring high spatial resolution
True
What are the two processes of analog-to-digital conversion (ADC)
Sampling
Quantization
Analog signal is is converted to digital signal
The digitized signals represent a specific location within the image matrix and is displayed as a specific brightness (shade of grey)
Analog to digital conversion (ADC)
Which has a wider latitude, CR or screen film?
CR
Screen film can only display approx. 30 shades of grey on a view box, CR can display approx. 100 000 grey levels
What produces better spatial resolution, small or large IR/IP with a fixed matrix size?
Smaller
(Smaller pixel size)
What is spatial resolution affected by in CR?
Phosphor layer thickness
Pixel size
Laser beam size
CR (2.5-5lpmm)
Screen film (100lpmm)
T/F
If improper part is selected (technique) the image may be processed incorrectly and fail to display properly
True
What is a major difference between film/screen receptors and digital receptors in regards to kvp?
Digital image contrast is no longer dependent on kvp
Radiographic noise produced by the random interaction of X-rays with an intensifying screen. This effect is more noticeable when very high rare earth systems are used at high kvp
Quantum mottle
What is the principal source of noise on an image?
-Mechanical defects (slow scan driver, fast scan driver)
-optical defects (laser intensity, scatter)
-computer defects (electronic noise, inadequate sampling/quantization)
What are some advantage of CR over screen film?
-Fewer repeat due to wider exposure latitude
-improved contrast resolution
-lower technical factors
-reduce patient dose
Matrix sizes will change with differing plate sizes to maintain spatial resolution
Fixed sampling frequency
Large IPs will result in poorer spatial resolution (larger pixel size) and small IPs will result in better spatial resolution (smaller pixel size)
Fixed matrix size
