Digital Radiography Lecture Notes

Introduction to Digital Radiography

• Focus: Components of cassettes in computed radiography (CR)
• CR: A digital imaging form using a cassette-based system.
• Similar to: Conventional film-based radiography.

Basic Functionality of CR

• Latent Image: Initial exposure results in an unprocessed image (like film).
• Needs processing: Done by a plate reader (discussed in later videos).

Components of CR Cassettes

• Cassettes: Have protective outer cases and a photo stimulable phosphor (PSP) plate.
• Key Components:
  1. Protective layer
  2. Phosphor layer
  3. Conductive or anti-static layer
  4. Support layer (base)
  5. Reflective or light shielding layer
• Materials: Hard plastics, light metals, carbon fibers.
• Function of Protective Cassette: Serves as a barrier with no impact on image production.

Details of the Layers

1. Protective Layer: Protects the phosphor layer (active component).
2. Conductive Layer: Grounds the imaging plate, reduces static charge.
3. Reflective Layer: Directs emitted light in the imaging plate reader.
4. Phosphor Layer: Most critical; where latent image is produced.
   • Composed of small particles able to store/release energy.
   • Common phosphors: Barium fluorohalide bromides and iodides with europium activators.

Energy Capture Process

• Photoelectric Absorption: Key interaction between X-ray photons and matter.
• Process:
  • X-ray photon strikes phosphor atom, ejecting an inner shell electron.
  • Energy from the photon excites the electron, becoming a photoelectron.
  • Photoelectrons interact with nearby electrons, exciting them to a higher energy state.
• Europium Activators: Act as electron traps (F-centers) storing high energy electrons.

Latent Image Storage and Release

• Storage: Latent image remains stored until released by laser light in the plate reader.
• Proportionality: Number of trapped electrons correlates to number of interacting X-ray photons.

Summary of Computed Radiography

• X-ray Imaging System: Utilizes cassettes to capture and process latent images into digital radiographs.
• Latent Image Creation: X-ray photons interact with phosphor atoms via photoelectric absorption, storing energy in the imaging plate.