Digital Radiography Series: Computed Radiography

Introduction

Focus: Components of cassettes in computed radiography (CR)
CR is a form of digital imaging using a cassette-based system, akin to traditional radiography
Cassettes record and store X-ray energy as an unprocessed, latent image
Processing latent images into usable radiographs is done via a plate reader

Protective Outer Case: Made of hard plastics, light metals, carbon fibers; serves as a protective barrier
Photostimulable Phosphor (PSP) Plate: Contains five key components:
1. Protective Layer: Protects the phosphor layer
2. Phosphor Layer: Active component, where latent image is produced
3. Conductive/Antistatic Layer: Grounds the imaging plate, reduces electrostatic charge
4. Support Layer/Base: Provides structural support
5. Reflective/Light Shielding Layer: Directs emitted light in the imaging plate reader

Composed of small particles that store and release energy
Common phosphors: Barium fluorohalide bromides and iodides with europium activators
Capture X-ray energy through photoelectric absorption
Process involves:
- Photoelectric Absorption:
  - X-ray photon strikes an atom in the phosphor layer, ejecting an inner shell electron
  - Absorbed photon energy creates a photoelectron
- Photoelectrons excite other nearby electrons, moving them to a high-energy conduction band
- Europium activators in F-centers trap high-energy electrons
- Latent image stored in this trap; number of trapped electrons proportional to interacting X-ray photons
- Release of stored energy facilitated by laser light in a plate reader

CR involves capturing latent images via cassettes and processing them into digital radiographs
Layers in cassettes, especially the active phosphor layer, are crucial for image production
Interaction of X-ray photons with phosphor atoms key to latent image creation

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