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What does the aluminum or lead do in a cassette?
Absorbs back scatter x ray photons
Felt; protects against static electricity buildup, dust collection and mechanical damage to plate.
What is the anti static material usually in PSP cassette and what's its functions?
Image plate definition
Thin sheet of plastic that records the image.
What are the layers of the imaging plate?
Protective
Phosphor
reflective
conductive
color
support
backing
Protective layer definition
Thin, tough, clear plastic that protects the phosphor layer
Phosphor layer definition
Layer that traps electrons during exposure. Also may contain a dye that deferentially absorbs the stimulating light to prevent as much spread as possible and functions much the same as dye added to conventional radiographic screens.
What is the phosphor layer made up of?
Photostimulable phosphor that is part of the barium fluorohalide family
Reflective layer definition
Layer that sends light in a forward direction when released in the cassette reader. May be black to reduce the spread of stimulating light and the escape of emitted light. Some detail is lost in this process.
Conductive Layer definition
Material that absorbs and reduces static electricity
Color Layer definition
Absorbs the stimulating light but reflects emitted light
Where is the color layer located?
Between the active and support layer
Support layer definition
gives the imaging sheet strength
Backing Layer definition
Soft polyer that protects back of cassette
What is the purpose of the barcode label
Allows technologist to match the image information with the patient identifying barcode on the exam request
What is the difference in image acquisition with film and PSP?
How the image is recorded
How is the image formed in PSP systems?
In PSP the remnant beam interacts with electrons in the barium fluorohalide crystals contained within the plate. The stimulated electrons in the crystals are trapped in the phosphor center.
What are the two types of PSP readers?
Point scan and Line scan
Point Scan reader
only a single laser point radiates the imaging plate at any point in time with this type of reader
What does a point scan reader have?
Optical stage, scanning laser beam, translation mechanics, light pick up guides, a photomultiplier, signal transformer or light amplifier and an analog to digital converter.
Line Scan reader
Based on simultaneous stimulation of plate one line at a time.
Acquisition of PLS occurs with a CCD linear array photodetector.
PSP image capture
1. Remnant photons interact with electrons in the barium fluorohalide crystals in plate
2. Electrons gain energy and become trapped
3. Cassette is fed into reader
4. Plate is removed from reader
5. Plate is scanned with a helium laser beam in a raster (Zig Zag) pattern
6. Laser gives energy to trapped electrons
7. Trapped electrons can now escape the active layer and emit visible blue light
8. Photodetectror detects lines of light intensity info
9. Photodetector amplifies the light and sends it to Analog to digital converter
10. Electrical signal is sampled and digitized to represent a specific location within the image matrix and displays as a specific brightness
11. Most of the electrons return to a lower energy state.
12. Plate is released by flooding it with light to remove any electrons still trapped
What are the two scan directions of the reader?
Fast scan and slow scan
Fast scan definition
Movement of laser across imaging plate
Slow scan definition
movement of plate through reader. AKA translation or subscan direction
What does the Laser function in doing?
Creates and amplifies a narrow intense beam of coherent light.
What does Laser stand for
Light Amplification of Stimulated Emission of Radiation
Why is the laser coherent?
All photons are traveling in the same direction and frequency.
Why does the laser require a constant power source?
To prevent output fluctuations
What kind of laser scans the imaging plate?
helium laser beam or solid state laser diodes.
How long is the wavelength for the laser beam?
633 nanometers
Translation
When the laser scans the plate multiple times
What does the scanning process produce?
Lines of light intensity info detected by a photodetector
What must be coordinated with the translation speed? Why?
the scan direction of the laser or the spacing of the scan lines will be affected
More angle of the laser beam will result in what?
More elliptical shape of the beam
If the beam shape were ignored what would happen?
The output of the screen would differ from middle to edges.
What does the photodetector do?
amplifies the light and sends it to an ADC
What does it mean to digitize a light signal from a photodetector?
Assigning a numerical value to each light photon
Factors affecting PSP resolution
Laser beam spot size, translation speed, sampling frequency, and the laser beam sweep in patient beam readers.
How often should plates be run under erase
once a week
What does erasure mode allow
surface of plate to be scanned without recoding generated signals
Why is it important to select the proper body part and position
So the proper conversions can take place
What is the kVp range required for radiography?
45-120
What is the k edge of phosphor imaging plate range? And what is the equivalent in kVp
30-50 keV- 60-110
why would we increase kVp
to decrease mAs
What happens when insufficient light is produced?
the image will appear grainy
What two factors should be considered when selecting the PSP imaging cassette?
Type and size
Grid selection factors
frequency, ratio, and focus
What does a high resolution plate contain
Thinner phosphor layer than standard plates
A thinner phosphor layer will ____ the sharpness of the image. Why?
Increase; the amount of light spreading laterally is reduced
What happens when the light spreads laterally?
Image appears blurry
What are high resolution plates limited to? What exams are they most often used for?
smaller cassettes, small extremities and mammo
If the matrix remains constant
FOV decreases
Pixel size decreases
spatial resolution of image increases
Miore effect definition
A wavy artifact that causes grid lines running parallel to laser scanning motion
Grid frequency
refers to the number of grid lines per centimeter or lines per inch
What is the typical grid frequency range?
80-152
Grid ratio
the relationship between the height of the lead strips and space
Shuttering is a postexposure image manipulation technique that
adds a black background to the original collimation edges
Why is the image recognition phase important?
Establishes the parameters that will determine collimation borders and edges and histogram formation
What are the 4 types of artifact?
Image plate
Plate reader
Image processing
Printer
Image Plate artifacts
cracks on plate within the reader, adhesive tape, hair that clings to cassette and lead coating
Plate reader Artifacts
Intermittent appearance of extraneous line patterns can be caused by problems in electronics of the plate reader.
Printer artifacts
Fine white lines that may appear on the image because of debris on the mirror in the laser printer
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