Digital 4, 5 and6
Card Set Information
Digital 4, 5 and6
PACS Chapter 4, 5 and 6
In CR, the radiographic image is recorded on a thin sheet of plastic known as the:
The imaging plate consists of the following layers:
Protective layer, phosphor layer, reflective layer, color layer, support layer, and backing layer
The protective layer of the imaging plate is responsible for:
protecting the phosphor layer
The phosphor layer of the imaging plate is a layer of ______ that traps electrons during exposure.
Phosphors in the phosphor layer are usually made of phosphors from the:
barium fluorohalide family
The CR cassette consists of a durable and lightweight ____ material backed by a thin sheet of ____ that absorbs x-rays.
Instead of an intensifying screen inside, the CR cassette has a ____ _____ that protects against ___ ____ buildup, dust collection, and mechanical damage.
antistatic material, static electricity
The layer of the imaging plate that sends light in a forward direction when released in the cassette reader:
The layer of the imaging plate that absorbs and reduces static electricity:
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
The support layer in the imaging plate consists of:
a semirigid material that gives the imaging sheet some strength
Soft polymer that protects the back of the cassette:
In CR, the remnant beam interacts with:
electrons in the barium fluorohalide crystals contained within the imaging plate
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.
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
What does “laser” stand for?
Light Amplification by Stimulated Emission of Radiation
A laser is a device that creates and amplifies a:
narrow, intense beam of coherent light
The laser beam passes through ___ ____ to an ___ ____ that directs the laser beam to the surface of the imaging plate
beam-shaping optics, optical mirror
Two types of lasers used to scan imaging plates:
helium laser beam and solid-state laser diodes
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
The plate movement through the scanner is known as:
Digitizing a signal, such as the light signal from the photomultiplier, is:
assigning a numeric value to each light photon
An entire analog image is divided into a matrix of pixels with a unique brightness value based on the:
energy stored on the phosphor
Typical matrix sizes are:
512x512, 1024x1024, or 2500x2500
The number of bits per pixel is known as:
The number of gray tones a pixel can produce is ___ to the power of the ____.
2, bit depth
The amount of detail in any image is known as it’s:
What determines spatial resolution in CR?
phosphor layer thickness and pixel size
The thinner the phosphor layer, the ____ the resolution.
Which has better spatial resolution: CR or film/screen? Why?
film screen has 10lines/mm as opposed to 2.5-5 lines/mm
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
Dynamic range is:
the number of recorded densities
In conventional radiography, speed is determined by:
size and layers of crystals in the film and the screen
The speed class in CR is a reflection of the amount of:
light emitted by the plate during the reading process
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
The phosphors in the imaging pate emit light according to the ___ and ____ of the laser beam as it scans the plate.
width and intensity
Imaging plates should be erased at least:
once a week to remove background radiation and scatter
Systems automatically erase the plate by:
flooding it with light to remove any electrons still trapped after initial reading
It is not recommended that kVp values less than ___ or more than ___ be used.
Optimum exposure ranges:
The mAs is selected according to the:
number of photons needed for a particular part
When insufficient light is produced, the image is grainy, a condition known as:
quantum mottle or quantum noise
Two important factors to be considered when selecting the CR imaging cassette:
type and size
Two types of imaging plates:
standard and high resolution
Typically, high resolution imaging plates are limited to size range and most often used for:
extremities, mammography, and other examinations requiring increased spatial resolution
The CR reader scans the imaging plate at a frequency of about
Grid line artifact also known as:
Grid selection factors:
frequency, ratio, and focus
Why is the use of a grid device more critical in CR than in conventional?
Because CR imaging plates are more sensitive to scatter
Grid frequency refers to the:
number of grid lines per centimeter or lines per inch
Typical grid frequency is between:
80 and 152 lines per inch
The higher the frequency of the grid, the:
less interference with the image, but greater risk for cut-off
The grid ratio is the relationship between the:
height of the lead strips to the space between them
Recommended grid ratios are ____ for mobile and ____ for departmental.
Regarding grid focus, most grids chosen by the department are:
parallel and focused
Parallel beams are less critical to ____ but should not be used with distances less than ___.
beam centering, 48”
Focused grids consist of lead strips angled to coincide with the:
divergence of the x-ray beam.
Focused grids must be used with ___ ____ and using a precisely ____ ____.
specific distances, centered beam
A black background that can be added around the original collimation to improve viewing but is not a replacement for proper pre-exposure collimation:
The amount of light given off by the imaging plate is converted into a signal that is used to calculate the:
exposure indicator number
Companies that use the “S” or Sensitivity Number as the exposure indicator:
Fuji, Phillips, and Konica
The “S” number is the amount of ____ emitted at 1 mR at ___kVp and has a value of ___.
luminescence, 80, 200
The higher the “S” number, the _____ the exposure.
The base exposure indicator number for all systems designates the:
middle of the detector operating range
Kodak uses what as the exposure indicator?
Exposure Index (EI)
EI plus ___ is equal to doubling exposure while an EI minus ___ is equal to halving exposure.
The higher the EI, the ____ the exposure.
the exposure indicator in an Agfa system is the:
lgM, or logarithm of the median exposure
For lgM, each step of .3 above or below 2.6 equals an exposure factor of:
X-ray photons are absorbed by the coating material and immediately converted into an electrical signal.
Two types of flat panel detectors:
Direct conversion and indirect conversion
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