Radiography with Photostimulable Storage Phosphor Equipment

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Questions and Answers

What is the primary function of the antistatic material in the cassette?

To absorb backscatter x-ray photons

To protect against static electricity build-up, dust collection and mechanical damage (correct)

To trap electrons during exposure

To convert stored light to an electrical signal

What is the purpose of the aluminum or lead backing in the cassette?

To convert electrical signals to digital image

To protect the imaging plate from light

To absorb x-ray photons during exposure

To absorb backscatter x-ray photons (correct)

What happens to the stored light in the phosphor layer during the reading process?

It is trapped by the antistatic material

It is absorbed by the protective layer

It is released and converted to an electrical signal (correct)

It is reflected back to the x-ray source

What is the primary component of the phosphor layer in the PSP imaging plate?

Barium fluorohalide Signup and view all the answers

What is the purpose of the conductive layer in the imaging plate?

To absorb and reduce static electricity Signup and view all the answers

In a cassette-based PSP system, what is the purpose of the barcode label on the cassette?

To match the image information with the patient-identifying barcode on the exam request Signup and view all the answers

What happens to the electrons in the barium fluorohalide crystals when the remnant beam interacts with them?

They are trapped in an area of the crystal known as the color or phosphor center Signup and view all the answers

What is the main difference between point scan and line scan readers in PSP systems?

The method of stimulating the imaging plate, one line at a time vs. one point at a time Signup and view all the answers

What is the term for the emission of light from the phosphor layer after stimulation by the relevant light source?

Photostimulated luminescence (PSL) Signup and view all the answers

What is the name of the process by which the laser creates and amplifies a narrow, intense beam of coherent light?

Light Amplification by Stimulated Emission of Radiation Signup and view all the answers

What is the purpose of the beam-shaping optics in the laser system?

To keep the beam size, shape, and speed largely independent of the beam position Signup and view all the answers

What determines the spatial resolution in PSP systems?

Phosphor layer thickness and pixel size Signup and view all the answers

What is the purpose of the mirrors in the laser system?

To filter out unwanted light

To direct the laser beam to the surface of the imaging plate

To ensure that the beam is positioned consistently

2 & 3 Signup and view all the answers

What is the primary reason for using a higher grid frequency in PSP systems?

To reduce the likelihood of moiré effects Signup and view all the answers

What is the primary advantage of using high-resolution imaging plates in PSP systems?

They have a thinner phosphor layer to reduce light spreading and increase image sharpness Signup and view all the answers

What is the primary reason for using a moving grid or Bucky in PSP systems?

To eliminate the interference between grid lines and the laser scanning motion Signup and view all the answers

Which of the following is a result of proper collimation?

Increased contrast Signup and view all the answers

What is the purpose of marking the patient exam with lead positional markers at the time of exposure?

To identify the patient's side and the technologist performing the exam Signup and view all the answers

What is the cause of dark line artifacts on the image?

Cracks in the imaging plate Signup and view all the answers

What is the purpose of orienting the stationary grid relative to the direction of the laser scan?

To reduce the likelihood of the moiré pattern error Signup and view all the answers

Other than the phosphor thickness, what other factors affect the resolution of PSP systems?

Laser beam spot size Signup and view all the answers

Why is it important to select the proper body part and position during PSP imaging?

To ensure proper conversion and image processing Signup and view all the answers

What is the primary reason for choosing a specific kilovoltage peak (kVp) value in digital imaging?

To achieve the correct balance between patient dose and part penetration Signup and view all the answers

What is the effect of higher kVp values on digital imaging?

Increased noise in the image Signup and view all the answers

Which of the following is a common cause of fine white lines appearing on a printed image?

Debris on the mirror in the laser printer Signup and view all the answers

What is the result of underexposure in digital radiography?

Quantum mottle Signup and view all the answers

What is the result of overexposure in digital radiography?

Reduced contrast Signup and view all the answers

What is the consequence of insufficient collimation in digital radiography?

Misrepresentation of the displayed image

Improper calculation of the exposure indicator

Overexposure of the imaging plate

Underexposure of the imaging plate

1, 2, & 3 Signup and view all the answers

What is the purpose of cleaning the laser printer in digital radiography?

To remove debris from the mirror Signup and view all the answers

What is the primary cause of artifacts from any hinges or other hardware present on the back of the cassettes?

Exposing the cassette with the back of the cassette toward the source Signup and view all the answers

What is the importance of proper handling of the cassette in digital radiography?

To prevent artifacts and ensure proper exposure of the imaging plate Signup and view all the answers

Study Notes

Photostimulable Storage Phosphor (PSP) Equipment

PSP systems differ from conventional radiography in that the cassette is a light-proof container that protects the imaging plate from light and handling.
The imaging plate stores an image formed by incident x-ray photons exciting phosphors.
Cassetteless systems use PSP technology without a cassette.

Cassette and Imaging Plate

The cassette is made of durable, lightweight plastic backed by aluminum or lead to absorb backscatter x-ray photons.
The imaging plate is a thin sheet of plastic with several layers:
- Protective layer: clear plastic for protection.
- Phosphor layer: traps electrons during exposure.
- Reflective layer: sends light in a forward direction when released.
- Conductive layer: absorbs static electricity.
- Color layer: absorbs stimulating light but reflects emitted light.
- Support layer: semi-rigid material for strength.
- Backing layer: soft polymer for protection.

Image Acquisition and Formation

The patient is radiographed in the same way as conventional radiography.
The remnant beam interacts with electrons in the barium fluorohalide crystals in the imaging plate.
The interaction gives energy to electrons, trapping them in the crystal.
The trapped signal remains for hours or days and can be released with a laser.

The Reader

There are two types of PSP readers: point scan and line scan.
Point scan readers use an optical stage, scanning laser beam, and photomultiplier.
Line scan readers use a charge-coupled device (CCD) linear array photodetector.
The reader scans the imaging plate with a laser to release the stored electrons.

Using the Laser to Read the Imaging Plate

The laser beam is shaped to ensure consistent beam size and speed.
A beam deflector moves the laser beam rapidly back and forth across the imaging plate.
The light collection optics direct the released phosphor energy to an optical filter and photodetector.
The scanning process results in the conversion of light into an electrical signal.

Digitizing the Signal

The electrical signal is sampled and digitized to represent a specific location within the image matrix.
The digitized signal is displayed as a specific brightness.

Spatial Resolution

Resolution is determined by phosphor layer thickness and pixel size.
The thinner the phosphor layer, the higher the resolution.
Factors affecting PSP resolution include laser beam spot size, translation speed, sampling frequency, and laser beam sweep.

Erasing the Image

The process of reading the image returns most electrons to a lower energy state, effectively removing the image from the plate.
Imaging plates are extremely sensitive to scatter radiation and should be erased regularly.

Preprocessing, Processing, and Forwarding the Image

Once the imaging plate has been read, the signal is sent to the computer for preprocessing.
The technologist can review the image, manipulate it if necessary, and send it to the quality control station and PACS.

Part Selection

The proper body part and position must be selected for the proper conversion to take place.
Selecting the improper part and/or position can result in a suboptimal image.

Technical Factors

Kilovoltage peak (kVp), milliamperage/second (mAs), and distance are chosen in the same manner as for film/screen radiography.
kVp is selected for penetration and tissue type.
mAs is selected according to the number of photons required for the body part.

Equipment Selection

Imaging plate selection: two types of imaging plates, standard and high resolution.
Grid selection: frequency, ratio, and focus.
High-resolution imaging plates are limited to smaller cassette sizes and are used for extremities and mammography.

Imaging Plate Artifacts

Cracks in the imaging plate appear as areas of lucency on the image.
Adhesive tape residue can leave marks on the imaging plate.
Static can cause hair to cling to the imaging plate.
Backscatter can cause dark line artifacts.

Plate Reader Artifacts

Intermittent appearance of extraneous line patterns can be caused by problems in the electronics of the plate reader.
Horizontal white lines can be caused by dirt on the light guide in the plate reader.### Plate Reader Artifacts
Insufficient erasure settings can result in residual images left on the imaging plate before the next exposure.
A faulty erasure lamp can also cause residual images.
The amount and location of residual images affect the results.
Plate readers can produce artifacts if multiple imaging plates are loaded in a single cassette and only one is extracted, leading to multiple exposures.

Grid Artifacts

The orientation of stationary grids relative to the laser scan direction is critical to prevent moiré pattern errors.
Grid lines must be perpendicular to the laser scan direction.
Moving grids do not typically produce moiré patterns due to blurred grid lines.
Vendors specify grid frequencies for their equipment to prevent moiré artifacts.

Printer Artifacts

Debris on the mirror in the laser printer can cause fine white lines to appear on the image.
Service personnel need to clean the printer to prevent this artifact.

Operator Errors

Insufficient collimation leads to improper calculation of the exposure indicator and misrepresentation of the displayed image.
Exposing the back of the cassette instead of the tube side can cause artifacts from hinges or other hardware.
Care should be taken to expose only the tube side of the cassette.
Underexposure produces quantum mottle, while overexposure reduces contrast.
Proper selection of technical factors is crucial for patient dose, image quality, and production of light from the imaging plate.

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Description

Learn about the differences between PSP systems and conventional radiography, including the role of imaging plates and cassette-based vs cassetteless systems.