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In CR, the radiographic image is recorded on a thin sheet of plastic known as the:
imaging plate
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The imaging plate consists of the following layers:
Protective layer, phosphor layer, reflective layer, color layer, support layer, and backing layer
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The protective layer of the imaging plate is responsible for:
protecting the phosphor layer
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The phosphor layer of the imaging plate is a layer of ______ that traps electrons during exposure.
photostimulable phosphor
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Phosphors in the phosphor layer are usually made of phosphors from the:
barium fluorohalide family
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The CR cassette consists of a durable and lightweight ____ material backed by a thin sheet of ____ that absorbs x-rays.
plastic, aluminum
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Instead of an intensifying screen inside, the CR cassette has a ____ _____ that protects against ___ ____ buildup, dust collection, and mechanical damage.
antistatic material, static electricity
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The layer of the imaging plate that sends light in a forward direction when released in the cassette reader:
reflective layer
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The layer of the imaging plate that absorbs and reduces static electricity:
conductive layer
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Newer imaging plates may contain a color layer, located between the active layer and the support, which:
absorbs the stimulating light but reflects emitted light
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The support layer in the imaging plate consists of:
a semirigid material that gives the imaging sheet some strength
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Soft polymer that protects the back of the cassette:
Backing layer
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In CR, the remnant beam interacts with:
electrons in the barium fluorohalide crystals contained within the imaging plate
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When electrons in the imaging plate are stimulated by the remnant beam, they enter the ____ _____ where they are trapped in an area of the crystal known as the ____ _____.
conductive layer, color or phosphor center.
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After exposure, the cassette is fed into a reader that:
removes the imaging plate and scans it with a laser to release the stored electrons
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What does “laser” stand for?
Light Amplification by Stimulated Emission of Radiation
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A laser is a device that creates and amplifies a:
narrow, intense beam of coherent light
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The laser beam passes through ___ ____ to an ___ ____ that directs the laser beam to the surface of the imaging plate
beam-shaping optics, optical mirror
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Two types of lasers used to scan imaging plates:
helium laser beam and solid-state laser diodes
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The laser beam is about ____ wide with a wavelength of ___ and scans the plate with a red laser light in a _____ pattern and gives energy to the trapped electrons.
100 micrometers 633 nm, raster
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The plate movement through the scanner is known as:
translation
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Digitizing a signal, such as the light signal from the photomultiplier, is:
assigning a numeric value to each light photon
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An entire analog image is divided into a matrix of pixels with a unique brightness value based on the:
energy stored on the phosphor
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Typical matrix sizes are:
512x512, 1024x1024, or 2500x2500
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The number of bits per pixel is known as:
bit depth
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The number of gray tones a pixel can produce is ___ to the power of the ____.
2, bit depth
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The amount of detail in any image is known as it’s:
spatial resolution
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What determines spatial resolution in CR?
phosphor layer thickness and pixel size
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The thinner the phosphor layer, the ____ the resolution.
higher
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Which has better spatial resolution: CR or film/screen? Why?
film screen has 10lines/mm as opposed to 2.5-5 lines/mm
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The loss of spatial resolution in CR is made up for by:
increased contrast resolution due to the dynamic range or number of recorded densities
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Dynamic range is:
the number of recorded densities
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In conventional radiography, speed is determined by:
size and layers of crystals in the film and the screen
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The speed class in CR is a reflection of the amount of:
light emitted by the plate during the reading process
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The amount of light emitted by the plate during the reading process in CR is related to:
the level of exposure received by the receptor
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The phosphors in the imaging pate emit light according to the ___ and ____ of the laser beam as it scans the plate.
width and intensity
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Imaging plates should be erased at least:
once a week to remove background radiation and scatter
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Systems automatically erase the plate by:
flooding it with light to remove any electrons still trapped after initial reading
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It is not recommended that kVp values less than ___ or more than ___ be used.
45, 120
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Optimum exposure ranges:
60-110 kVp
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The mAs is selected according to the:
number of photons needed for a particular part
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When insufficient light is produced, the image is grainy, a condition known as:
quantum mottle or quantum noise
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Two important factors to be considered when selecting the CR imaging cassette:
type and size
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Two types of imaging plates:
standard and high resolution
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Typically, high resolution imaging plates are limited to size range and most often used for:
extremities, mammography, and other examinations requiring increased spatial resolution
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The CR reader scans the imaging plate at a frequency of about
2000x2000 pixels
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Grid line artifact also known as:
moire’ pattern
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Grid selection factors:
frequency, ratio, and focus
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Why is the use of a grid device more critical in CR than in conventional?
Because CR imaging plates are more sensitive to scatter
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Grid frequency refers to the:
number of grid lines per centimeter or lines per inch
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Typical grid frequency is between:
80 and 152 lines per inch
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The higher the frequency of the grid, the:
less interference with the image, but greater risk for cut-off
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The grid ratio is the relationship between the:
height of the lead strips to the space between them
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Recommended grid ratios are ____ for mobile and ____ for departmental.
6:1, 12:1
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Regarding grid focus, most grids chosen by the department are:
parallel and focused
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Parallel beams are less critical to ____ but should not be used with distances less than ___.
beam centering, 48”
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Focused grids consist of lead strips angled to coincide with the:
divergence of the x-ray beam.
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Focused grids must be used with ___ ____ and using a precisely ____ ____.
specific distances, centered beam
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A black background that can be added around the original collimation to improve viewing but is not a replacement for proper pre-exposure collimation:
Shuttering
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The amount of light given off by the imaging plate is converted into a signal that is used to calculate the:
exposure indicator number
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Companies that use the “S” or Sensitivity Number as the exposure indicator:
Fuji, Phillips, and Konica
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The “S” number is the amount of ____ emitted at 1 mR at ___kVp and has a value of ___.
luminescence, 80, 200
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The higher the “S” number, the _____ the exposure.
lower
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The base exposure indicator number for all systems designates the:
middle of the detector operating range
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Kodak uses what as the exposure indicator?
Exposure Index (EI)
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EI plus ___ is equal to doubling exposure while an EI minus ___ is equal to halving exposure.
300/300
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The higher the EI, the ____ the exposure.
higher
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the exposure indicator in an Agfa system is the:
lgM, or logarithm of the median exposure
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For lgM, each step of .3 above or below 2.6 equals an exposure factor of:
2
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X-ray photons are absorbed by the coating material and immediately converted into an electrical signal.
Direct Conversion
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Two types of flat panel detectors:
Direct conversion and indirect conversion
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The DR plate has a radiation conversion material or photoconductor usually made of ____ ____. This material absorbs x-rays and converts them to electrons which are stored in the ____.
Amorphous Selenium, TFT detectors
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