Lecture on Digital Imaging

Introduction

• Simplified discussion on digital imaging
• Focus on computed radiography (CR) and digital radiography (DR)
• Digital imaging is the umbrella term for CR and DR

Digital Imaging Overview

• Defined as methods of getting pictures that can be viewed/manipulated on a computer
• Examples include cell phone cameras and x-ray technologies
• Digital imaging started with CT scanners in the 1970s

Analog vs. Digital

• Digital: Discrete, on/off state (e.g., digital watches, Daft Punk)
• Analog: Continuous change, no discrete state (e.g., traditional watches, Led Zeppelin)

Computed Radiography (CR)

• Uses storage phosphor plates inside CR cassettes
• Requires a reading and viewing station
• Similar workflow to film but different technology
• Key Component: Photostimulable Phosphor Plate (PSP)
  • Layers: Protective, Phosphor (Active), Reflective, Conductive, Support
  • Phosphor layer traps electrons using barium fluorohalide
  • Erased by exposure to strong light

CR Workflow

• Cassette placed behind the patient, x-rays pass through to PSP plate
• Static prevention critical to avoid image artifacts
• Reading involves laser scanning, photomultiplier amplifies the signal
• Analog-to-digital conversion
• Matrix size affects spatial resolution; larger matrix means higher resolution

Digital Radiography (DR)

• Includes Direct and Indirect DR
• Direct DR: Uses amorphous selenium, TFT arrays, direct conversion, like cell phone cameras
• Indirect DR: Involves an additional light conversion step with cesium iodide scintillator

Image Quality

• Spatial resolution: Amount of detail, depends on matrix size
• Dynamic range: Range of densities captured
• Image contrast resolution: Ability to differentiate tissue densities

Detective Quantum Efficiency (DQE)

• Measures efficiency of converting input signal to useful output
• High DQE is preferred for capturing low contrast objects

Additional Topics

• Exposure latitude and dynamic range: Ability to capture over/underexposure
• Monitors also involve matrices affecting spatial resolution
• Informatics: Systems like HISS (billing/patient info), RIS (exam tracking), DICOM (image standard), PACS (storage)

Conclusion

• Emphasis on understanding and accurate usage of digital imaging technology
• Importance in medical imaging and patient care