Ch 4 Photostimulable Phosphor Image capture Flashcards
What is one way of acquiring and processing digital radiographic images?
with photostimulable phosphor systems (PSP)
Are PSP cassette based or cassette less?
they are both
Basically describe a PSP cassette
the cassette is a lightproof container that protects an imaging plate from light and handling
The PSP imaging plate takes the place of the radiographic film and is capable of …
storing an image formed by incident x-ray photon excitation of phosphors
During the reading process of a cassette-less PSP system, the phosphor…
releases the stored light and converts it into an electrical signal, which is then digitized.
The PSP cassette looks like…
a conventional screen/film cassette.
The PSP cassette consists of…
a durable, lightweight plastic material. The cassette is backed by a thin sheet of aluminum or lead and contains an antistatic material (felt)
What is the function of the aluminum or lead that backs the PSP cassette?
it absorbs backscatter x-ray photons
What is the function of the antistatic material?
it protects against static electricity buildup, dust collection, and mechanical damage to the plate
In PSP systems the image is recorded on…
a thin sheet of plastic known as the imaging plate
How many layers does an imaging plate have?
7
What are the layers of the imaging plate?
- protective layer
- phosphor layer
- reflective layer
- conductive layer
- color layer
- support layer
- backing layer
What is the protective layer of the PSP plate?
a very thin, tough, clear plastic that protects the phosphor layer
What is the phosphor layer also known as?
the active layer
Explain the phosphor layer.
It is a layer of photostimulable phosphor that traps electrons during exposure. It is usually made of phosphors from the barium fluorohalide family. This layer may also contain a dye that differentially 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 reflective layer?
a layer that sends light in a forward direction when released in the cassette reader. This layer may be black to reduce the spread of stimulating light and the escape of emitted light. Some detail is lost in this process.
What is the conductive layer?
a layer of material that absorbs and reduces static electricity.
What is the color layer?
it is on newer plates and located between the active layer and the support, that absorbs the stimulating light but reflects emitted light
What is the support layer?
a semi-rigid material that gives the imaging sheet some strength
What is the backing layer?
a soft polymer that protects the back of the cassette
What does a PSP cassette have on the back?
a window with a barcode label or barcode sticker to allow the tech to match the image information with the patient ID code
A PSP cassette may also have a color coded sticker for what reason?
to indicate the appropriate orientation of the cassette in relation to the patient
With a PSP system, how is the exposure recorded?
The remnant beam interacts with electrons in the barium fluorohalide crystals contained within the imaging plate. The interaction stimulates, or gives energy to, electrons in the crystals, trapping them in an area of the crystal known as the color or phosphor center.
How long will the trapped signal remain on the PSP plate?
for hours or even days…actually, the image never goes away, it just isn’t seen
How many different PSP READERS? what are they?
2; point scan and line scan
What do point scan readers have?
an optical stage, a scanning laser beam, translation mechanics, a light pickup guide, a photomultiplier, a signal transformer/amplifier, and an analog to digital converter (ADC)
In a point scan reader how many laser points radiate this imaging plate?
only one
Line scan readers are based on what?
simultaneous stimulation of the imaging plate one line at a time
How is the acquisition done with a line scan reader.
with a charge coupled device (CCD) linear array photodetector.
What does PSL stand for?
photostimulated luminescence
What is PSL?
the emission of light from the phosphor layer after stimulation by the relevant light source
Unlike the point scan reader, the line scan uses what to scan?
a scanning module that contains several linear laser units and optical light collection lenses. The line scan system requires a lens array to focus each laser beam to a corresponding point on the CCD array.
What are the 2 scan directions in a PSP reader?
- fast scan direction
2. slow scan direction
What is fast scan direction?
the movement of the laser across the imaging plate known as scan
What is slow scan direction?
the movement of the imaging plate through the reader known as translation or sub-scan direction
What does laser stand for?
light amplification of stimulated emission of radiation
What does coherent light mean?
it is coherent because all of the photons are traveling in the same direction at the same frequency
What does the photodetector do in the PSP reader?
it amplifies the light and sends it to an ADC.
Why does the translation speed of the plate have to be coordinated with the scan direction of the laser?
If not, the spacing of the scan lines will be affected
