Chapter 4: Photostimuable Phospher (PSP) Image Capture

A cassette is a light-proof container that protects an imaging plate from light and handling

How do cassette-based PSP systems differ from conventional radiography?

Imaging Plate

In PSP image capture, what takes the place of radiographic film and is capable of storing an image formed by incident X-ray photon excitation of phosphors?

A cassette

Cassette-less systems similarly use PSP technology, but without the need for what?

phospher / light / electrical

During the reading process, the ____________ releases the stored __________ and converts it to an _____________ signal, which is digitized

Like a film/screen cassette

What does a PSP cassette look like?

Durable, lightweight plastic

What material does the PSP cassette consist of?

Backed with aluminum or lead to absorb backscatter X-ray photons

What is the PSP cassette backed with and why?

Antistatic material (usually felt)

In addition to holding the PSP plate, what material does the cassette also contain?

- Static electricity build-up

- Dust collection

- Mechanical damage to the plate

What three things does the antistatic material protect against?

Imaging Plate

In PSP systems, what refers to the thin sheet of plastic on which the radiographic image is recorded?

Protective Layer

What layer of the imaging plate is a very thin, tough, clear plastic that protects the phosphor layer?

Phosphor Layer (Active Layer)

What layer of the imaging plate is a layer of photostimulable phosphor that "traps" electrons during an exposure?

Phosphors from the barium fluorohalide family

What is the phosphor layer (active layer) usually made of?

Reflective Layer

What layer of the imaging plate is the layer that sends light in a forward direction when released in the cassette reader?

To reduce the spread of stimulating light and escape of emitted light

Why may the reflective layer be black?

Details can be lost

What can happen to the details of an image in the reflective layer?

Conductive Layer

What layer of the imaging plate is the layer of material that absorbs and reduces static electricity?

Color Layer

What layer of the imaging plate is the layer of material that is between the phosphor layer and support layer that absorbs stimulating light but reflects emitted light?

Support Layer

What layer of the imaging plate is the semi-rigid material that gives the imaging sheet some strength?

Backing Layer

What layer of the imaging plate is a soft polymer that protects the back of the cassette?

Barcode Label/Sticker

In cassette-based PSP systems, what is referred to as the window on the cassette that allows the technologist to match the image information with the patient-identifying barcode on the examination request?

They must be scanned and connected to the patient position or exam menu

For each new examination, what must happen to the patient-identifying barcode and the barcode label on the cassette?

image / examination worklist

In cassetteless PSP systems, the ___________ must be matched with the _____________ ______________ on the computer

A colored mark or sticker

What can be included in a cassette-based system that indicates the appropriate orientation of the cassette in relation to the patient?

Remnant beam

During the image formation of a PSP system, what interacts with electrons in the barium fluorohalide crystals contained within the imaging plate?

It stimulates (gives energy) electrons in the crystals, trapping them in an area of the crystal known as the color or phosphor center (F-Trap)

During image formation in a PSP system, when the remnant beam interacts with the barium fluorohalide crystals, what happens?

Latent Image

What kind of image is stored in the phosphor layer of the PSP plate?

For hours or even days

During image formation in a PSP system, how long does the trapped signal remain?

Immediately

During image formation in a PSP system, when should the imaging plate be processed?

It can never be completely erased

During image formation in a PSP system, because a certain amount of exposure remains trapped, what happens to the imaging plate?

Do not interfere with following exposures

Although the imaging plate may still have residual trapped electrons, they are so few in number that they?

The reader

Following an exposure, what is the PSP cassette fed into that removes the imaging plate, scans it with a laser to release the stored electrons, and reads the imaging plate?

The laser

What is the device that creates and amplifies a narrow, intense beam of coherent light?

Light Amplification of Stimulated Emission of Radiation

What does laser stand for?

Constant power source

What does the laser require to prevent output fluctuations?

Beam-shaping optics to an optical mirror

What does the laser beam pass through that directs the laser beam to the surface of the imaging plate?

eliptical

The more angled the laser beam, the more ___________ the shape of the beam

Scans the plate with red light in a raster (zigzag) pattern

What does the reader use to scan the imaging plate, and how is it done?

Gives them energy

What does the laser do to the trapped electrons on the imaging plate?

2 eV

What is the approximate amount of electron volts emitted by the red laser light that is necessary to energize the trapped electrons on the imaging plate?

Blue light is emitted at an energy of 3eV as they relax into lower energy levels

When the extra energy allows the trapped electrons to escape the active layer, what happens?

Photostimulated Luminescence (PSL)

What is the process of a PSP reader scanning an imaging plate with a laser to release stored energy as light?

Photodetector (Photodiode / Photomultiplier)

What device detects and amplifies the light and sends it to an analog-to-digital converter (ADC) or converts light photons into electrons?

Bright White Light

Any remaining energy that is left on the imaging plate is erased with what?

Translation

What is the movement of the imaging plate through the PSP reader as the laser scans it?

The scan direction of the laser

What must the translation speed of the imaging plate match?

50 cassettes per hour

Although there are variances among PSP reader manufacturers, what is the typical throughput for cassettes?

Fading

What refers to the time it takes for the latent image to disappear?

25 / 8

Photostimulable luminescence (PSL) decreases by about _____% after ____ hours

Spatial resolution

What refers to the amount of detail present in any image?

Bits

What refers to the pieces of information contained within each pixel?

Bit Depth

What refers to the number of bits per pixel that defines the number of available shades of gray in each pixel?

Phospher layer thickness and pixel size

What determines the spatial resolution in PSP?

thinner / higher

The ___________ the phospher layer ➜ The ___________ the spatial resolution

- 2.5 - 5 lp/mm

- Less detail

- What is the line pair frequency for PSP resolution?

- What does this result in?

Sampling Frequency

What can affect the spatial resolution in PSP image capture?

Because of a greater number of available shades of gray that can be displayed (bit depth)

Why is it more difficult to discern the difference in resolution in PSP imaging?

No

Even though there are more shades of gray that can be displayed with PSP imaging, does this mean an image contains additional detail?

Erasure Mode

What does PSP readers have that allows the surface of the imaging plate to be scanned without recording the generated signal?

Scatter radiation

What are PSP imaging plates extremely sensitive to, that if not erased, can cause a build-up of background signal?

Every 48 hours

To ensure that PSP imaging plates are erased properly, how often should they be run under an erasure cycle to remove built-up background radiation and scatter?

By flooding it with bright white light

How do systems automatically erase the PSP imaging plate to remove any electrons still trapped after the initial plate reading?

Should be erased

What should be done to cassettes if the last time of erasure is unknown?

- Anhydrous Ethanol

- Camel Hair Brush

- Lint-Free Cloth

What are 3 things that can be used to clean PSP imaging plates?

Prior to exposure to the IR or after exposure

Depending on the type of system being used, when does the technologist choose the body part being imaged?

So that technologists know which cassette goes with which body part

Because body part selection is done after an exposure when using a cassette-based system, why is it imperative to keep cassettes apart?

So proper conversion can take place

When using PSP systems, why is it important to select the proper body part and position?

The image may be processed incorrectly and fail to display properly

In PSP systems, what happens if the improper part and/or position is designated?

Through complex mathematical computer algorithms

In PSP systems, how is image recognition accomplished?

False - It's not acceptable

T/F - In a PSP system, it is acceptable to select a body part or position other than that being performed simply because it looks better

Service Personnel

In PSP systems, if the proper exam or part selection results in suboptimal images, who should be notified of the problem so it may be corrected?

Overexposure of the patient and repeated exams

What can improper menu selections lead to?

kVp, mA, and distance

What technical factors are chosen in the same manner in digital projection systems as in conventional film/screen radiography?

- Penetration and tissue type

- According to the number of photons required for the body part imaged

- Traditionally, what was kVp chosen for?

- Traditionally, how was mAs chosen?

45 / 120

It is not recommended that kVp values lower than ____ or greater than ____ are used because those values may be inconsistent and produce too little or too much excitation of the phosphors

60 to 110 kVp

Because the k-edge of phosphor imaging plates ranges from 30 to 50 keV, what are the optimal kVp exposure ranges?

dose / penetration

It is vital that the proper balance between patient _______ and part ____________ be achieved

higher / lower

A major difference between film/screen radiography and digital receptors is that digital image contrast is no longer dependent on kVp, so ___________ kVp values can be used allowing for __________ mAs values

Computer Processing

What is contrast determined by in PSP image capture?

Quantum Mottle or Quantum Noise

What refers to an image being grainy due to insufficient light produced?

larger / more gradual

The _______ the dynamic range, the _________ _________ the gray scale representing the range from maximal to minimal x-ray intensity

The better the contrast resolution

The greater the dynamic range, the what?

Type and Size

What are the two important factors that should be considered when selecting the PSP imaging cassette?

Standard and High Resolution

For PSP systems, what are the two types of imaging plates that most manufacturers produce?

On the outside

Where should PSP cassettes be marked to indicate high-resolution imaging plates?

High-Resolution

Which type of PSP imaging plate contains a thinner phosphor layer?

Greater image sharpness due to reduced light spreading

Since high-resolution PSP imaging plates contain a thinner phosphor layer, what does this result in?

In mammography and for extremities

Because high-resolution PSP imaging plates are limited to smaller cassette sizes, where are they most often used?

decreases / decreases / increases

If the matrix remains constant, as the field of view ________, pixel size also __________, and the spatial resolution ___________

Scatter outside the initial collimation; Increase contrast resolution

If the appropriate PSP imaging plate is selected, what is eliminated? What does this do?

Interferes with the image

What do grid lines that are projected onto the imaging plate while using a stationary grid do to the image?

Moiré Pattern

What is the wavy artifact caused by grid lines running parallel to the laser scanning motion?

The oscillating motion

What in a moving grid or a bucky blurs grid lines and eliminates image interference?

Frequency, ratio, focus

What are the grid selection factors?

Grid Frequency

What refers to the number of grid lines per centimeter or lines per inch?

higher / more / finer / less

The ________ the frequency or ________ lines per inch, the _______ the grid lines in the image and the _______ they interfere with the image

More scatter

When exposing a patient, a larger volume of tissue is being irradiated, so what will be produced?

Collimation

What refers to the reduction of the area of the beam that reaches the patient through the use of two pairs of lead shutters encased in a housing attached to the X-ray tube?

Increased contrast resolution

Because collimation reduces scatter, what does it result in?

Shuttering

What refers to a postexposure image manipulation that adds a black background around the original collimation edges, virtually eliminating the distracting white or clear areas?