Digital Image Artifacts in Medical Imaging

Digital Image Artifacts in Medical Imaging

Definition of Artifacts

  • Artifacts: False visual features on a medical image that either simulate or obscure actual tissues, making accurate diagnosis difficult.
  • Artifacts can mask or mimic clinical features and must be avoided during image acquisition.

Classification of Artifacts

1. Hardware-Induced Artifacts

  • Originates from physical components of the imaging system (e.g., detector, digitizer).
  • Examples:
    • Cracks in imaging plates show as bright/dark streaks.
    • Dirty or malfunctioning digitizer rollers can create linear artifacts.
    • Poorly functioning data cables may induce alternating dark/light lines.

2. Software-Induced Artifacts

  • Caused by errors in image processing software.
  • Examples:
    • Uberschwinger or halo artifacts due to aggressive edge enhancement, mimicking outlines of bones or metals.
    • Ghosting from rapid consecutive images without adequate resetting.

3. Image Acquisition Artifacts

  • Result from errors made by the technologist during image capture.
  • Examples:
    • Incorrect patient positioning can lead to incomplete or distorted imagery.
    • Motion blur due to patient movement during exposure, resulting in ghost images.
    • Double exposures from reuse of inadequately erased imaging plates, creating overlapping images.

Common Artifacts

1. Double Exposure

  • Cause: Two exposures on the same imaging plate.
  • Remedy: Proper knowledge of X-ray equipment to ensure correct usage.

2. Backscatter Artifacts

  • Cause: Scattered radiation reflecting off nearby objects and re-entering the image system.
  • Remedy: Proper cassette positioning and collimation improvements.

3. Focal Radiopacities

  • Cause: Dust or fingerprints on imaging plates.
  • Remedy: Regular cleaning using ethyl alcohol.

4. Quantum Mottle (Noise)

  • Cause: Too low exposure settings.
  • Remedy: Properly adjust exposure factors based on the patient's body part and build.

5. Moiré Pattern

  • Cause: Use of grids with low frequencies.
  • Remedy: Use grids with 60 lines/cm or more, aligning them perpendicularly to the scanner's scan lines.

Data Transmission Issues

Missing Lines or Pixels

  • Cause: Power failure during image transmission.
  • Remedy: Repeat the radiograph.

Digital Processing Artifacts

Alternating Radiopaque and Radiolucent Lines

  • Cause: Data cable failures in the digitizer or CR reader.
  • Remedy: Replace data cables.

Uberschwinger Artifact (Halo Effect)

  • Cause: Edge enhancement algorithms that over-amplify contrast at metal boundaries (prosthetics, implants).
  • Remedy: Reduce edge enhancement effects in images containing metal.

CR Specific Artifacts

Exposure Through Back of Cassette

  • Cause: Poor knowledge of cassette construction.
  • Remedy: Educate on proper handling of cassettes.

Kink Marks

  • Cause: Mishandling of imaging plates during cleaning or transport.
  • Remedy: Handle with care.

Light Bulb Effect

  • Cause: Backscatter radiation due to an uncollimated beam, often with high exposure settings.
  • Remedy: Lower kVp or improve collimation.

Roller and Plate Reader-Induced Artifacts

Disparity Artifact

  • Cause: Malfunctioning rollers in the digitizer.
  • Remedy: Periodically clean rollers.

Ghost Images

  • Cause: Incorrect body part selection or malfunctioning bulbs.
  • Remedy: Ensure correct selections and replace bulbs as needed.

Digital Radiography Artifacts

Image Compositing Artifact

  • Cause: Misalignment during image stitching.
  • Remedy: Archive and provide access to original source images for potential re-analysis.

Detector Image Lag and Ghosting

  • Cause: Residual signals from previous exposures.
  • Remedy: Allow sufficient decay time between exposures to clear previous signals.

Backscatter

  • Description: Artifacts caused by backscatter can significantly distort images and need prevention through correct positioning and technology use.

Summary

  • Artifacts in digital imaging can severely impact diagnostic accuracy. Prevention strategies focus on proper equipment use, regular maintenance, and understanding image acquisition principles to minimize these effects.