Chapter 4 Flashcards
psp systems are either
cassette based or cassette less
cassette based psp systems different from conventions in that the cassette is
simply a light proof container that protects an imaging plate from light and handling
The PSP cassette consist of a
Durable, lightweight, plastic material
The PSP cassette is backed by thin sheet of ____ or _____ that absorbs back scatter x-ray photons
aluminum or lead
The PSP cassette contains a ____ material to protect against static, electricity, buildup, dust collection, and mechanical damage
anti static
felt
And PSP systems imaging plate consist of several layers
Protective layer, phosphor or active layer, reflective layer, conductive layer, color layer, support layer, and backing layer
In PSP systems, the radiographic image is recorded on a thin sheet of plastic known as
imaging plate
Protective layer
Very thin, tough clear plastic that protects the phosphor layer
This is a layer of photo stimulable phosphor that traps electrons during exposure. made of barium floral halide, and this may also contain a dye that differentially absorbs the stimulating light to minimize the light spread as much as possible
phosphor layer
Layer that sends light into a forward direction when released in the cassette reader, may be black to reduce the spread of stimulating light and escape of emitted light
reflective layer
What layer absorbs and reduces static electricity?
Conductive layer
located between the active layer in the support layer that absorbs a stimulating light, but reflects emitted light
color layer
Semi rigid material that gives imaging sheet some strength
support layer
Soft polymer that protects the back of the cassette
Backing layer
Cassette base, PSP systems containing window with a
Barcode label
If the cassette was correctly orientated, that image will be displayed
Correct
and PSP, the remnant beam interacts with electrons in the barium fluorohalide crystals contained within the imaging system. This interaction stimulates, or gives energy to electrons in the crystal, trapping them in the area of the cassette known as the.
color or phosphor center
Two types of PSP readers
Point scan and line scan
Contains an optical stage, a scanning laser beam, translation mechanics, light pick up guides, a photo multiplier, a signal transformer amplifier, and an analog digital converter
point scan readers
line scan readers are based on
simultaneous stimulation of the imaging plate, one line at a time
with light scan readers, the acquisition of Photostimulated luminance occurs with a
CCD linear array photodetector
PSL refers to the
The emission of light from the phosphor, after stimulation by the relevant light source
The line scan system requires a
lens array to focus each laserbeam to a corresponding point on the CCD array
What are the two scan directions?
fast scan, and low scan
Fast scan direction
The movement of the laser across the imaging plate
slow scan direction (translation, or subscan)
The movement of the imaging plate through the reader
Light amplification of stimulated emission of radiation
laser
device that creates and amplifies a narrow, intense beam of coherent light
laser
The laser requires a
Constant power source to prevent output fluctuations
The laser beam passes through beam shaping object to an
Optical mirror that directs the laser beam to the surface of the imaging plate
During the reading process, the imaging plate is scanned with a
Helium laser beam (more recently a solid state laser diode)
The laserbeam is about ____ wide, with a wavelength of _____
100 micrometers
633 nanometers
(670-690 for solid state )
The laserbeam scan the plate with a
Red light in a raster pattern
The red laser light is admitted at approximately
Two electron volts, which is necessary to energize the trapped electrons
The energy from the red laser light allows the trapped electrons to escape the active layer where the emit visible blue light at an energy of
3 electron volts as they relax to lower energy levels
As the imaging plate moves through or remain stationary in the reader, the laser scans across the imaging plate
Multiple times
The plate movement through the scanner is known as translation, because
Because it moves in a parallel manner at a certain rate through the reader
As the imaging plate is being scanned the process produces lines of light intensity information that are detected by a
Photodetector
Amplifies a light and send it to the ADC
Photo detector
The translation speed of the plate must be coordinated with the skin direction of the laser or the
Spacing of the scan lines will be affected
The more angled the beam is the more
Elliptical in the shape of the beam
The beam is shaped by special _____ that keeps the beam size, shape, and speed, largely independent of the beams position
optics
A beam deflector moves the laser beam rapidly back-and-forth across the imaging plate to stimulate the
phosphors
because the type of phosphor material in the imaging plate has an effect on the amount of energy required
Did laser in the imaging plate should be designed to work together
The typical throughput is _____ cassettes per hour
50
Digitizing a signal
The signing a numerical value to each light photon
In film screen radiographic resolution at its best is limited to
10 LP/MM
PSP imaging resolution is approximately
2.5- 5 LP/MM
Resolution detail is affected by the
Laserbeam spot size, translation speed, sampling, frequency, and laserbeam sweep
The smaller the diameter of the laserbeam
The higher the spatial resolution
Slower translation speed all allows more
Exposure to be detected
The higher the sampling frequency the more
exposure detected
Imaging plates are extremely sensitive to scatter radiation and should be
Erase to prevent a buildup of background signal
At least, once a week, the plates should be ran through a
Erase cycle to remove background radiation, and scatter
Systems automatically erase the plate by flooding it with
Light to remove any electrons, trapped after the initial reading
When using a cassette base system, the selection of the body part is usually done
After exposure
traditionally, KVP was chosen for _____ and _____, and mAs according to the
penetration and tissue type
number of photons required for that body part
KVP values range from _____ to ____ of most digital projection systems
45-120
The k edge of phosphor imaging plates ranges from ___ to ___
30-50 kEv
The process of _____ is exactly the same in film
attenuation
Major difference between film and digital is the image contrast is no longer dependent on
kvp
in digital imaging contrast is determined by
Computer processing
Two important factors should be considered when selecting the PSP imaging cassette
type and size
Two types of imaging plates
Standard and high resolution
Cassette should be marked on the outside to indicate
high resolution imaging plates
High resolution, imaging plates contain a ____ compared to the standard plates
Thinner phosphor layer
The thinner phosphor layers result in greater image sharpness, because of the
Reduced amount of light spread
light spread can occur with any image capture system that involves
Release of light
High resolution imaging plates are limited to
Smaller cassette size is used for extremities mammography
The oscillating motion of a moving grid or buck blurs the grid lines and eliminates the
moire effect
PSP systems are more sensitive to low levels of radiation so the use of ____ is important
grid
Grid selection factors
Frequency, ratio, and focus
The number of gridlines per inch or centimeter
grid frequency
The higher the grid frequency or more lines per inch
The finer the grid lines in the image, and less they interfere
Typical grid frequencies
80-152 lines /inch
some manufacturers recommend no fewer than ___ lines per inch, and strongly suggest grid frequencies greater than ____
103, 150
The closer the grid frequency is to the laser scanning frequency, the greater likelihood of frequency harmonics, or matching, and the more likely the risk of
moire effects
The ratio of the height of the lead strips to the distance between them
Grid ratio
Grade ratios of ___ would be good for mobile
6:1
Grid ratios of ____ would be good for departmental
12:1
Most grids chosen by radiography departments are
parallel and focused
Parallel grids are less critical to beam centering, but should not be used at a distance less than
48 inches
Consist of lead strips, angled to coincide with the divergence of the x-ray beam, and must be used with specific distances using a precisely centered beam
focused grid
Increasing the collimation
Increases the contrast
this is extremely important and establishing the parameters that determine collimation borders and edges and histogram formation
image recognition phase
Image, recognition, phase
agfa uses the term
collimation
image recognition phase
carestream
segmentation
image recognition phase
fuji
Exposure data, recognition
For common types artifacts
Image plate artifacts
imaging processing artifacts
Plate reader artifacts
printer artifacts
this artifact can happen because of incorrect part, chosen on control panel
incorrect sampling
Poor technique
image processing artifact
Intermittent appearance of the extraneous line pattern that can be caused by problems in the electronics of the plate reader
plate reader artifacts
The gridlines must be ____ to the laser scan direction
perp
Artifact to wear fine white lines may appear on the image because of debris on the mirror in the laser printer
printer artifacts
