Patient-Image Optimization in Radiography

Patient-Image Optimization

• Patient/Subject Factors: affect how x-rays are absorbed, influencing image quality.

  • Subject Contrast: Degree of differential absorption between tissues.
    • High subject contrast: Large difference in x-ray absorption, like bone and soft tissue.
    • Low subject contrast: Small difference in x-ray absorption, like different types of soft tissue.
  • Patient Thickness: Thicker sections attenuate more x-rays, affecting contrast.
  • Tissue Mass Density: Denser tissues (bone) absorb more x-rays than less dense tissues (lung).
  • Effective Atomic Number: Higher atomic numbers (bone) absorb more x-rays than lower atomic numbers (soft tissue).
  • Object Shape: Influences x-ray attenuation and contrast.

• Image-Quality Factors: Influence the overall quality of a radiographic image.

  • Spatial Resolution: Ability to image small objects with high contrast.
  • Contrast Resolution: Ability to distinguish subtle differences in tissue density.
  • Distortion: Geometric distortion of the image due to misalignment.
  • IR Response: The response of the image receptor to the x-rays.

Radiographic Quality

• Radiographic contrast is influenced by both image receptor contrast and subject contrast.

Body Types

• Hypersthenic: Large frame, overweight.
• Sthenic: Average, strong, active.
• Hyposthenic: Thin, but healthy appearance.
• Asthenic: Small, frail, emaciated.

Pathologies

• Destructive Pathologies: Often require a decrease in technique due to reduced tissue density.
  • Examples: Osteoporosis, Osteomalacia, Emaciation.
• Non-Destructive Pathologies: Many diseases don’t significantly affect tissue density.
  • Examples: Fractures without swelling, Ulcers, Diverticula.

Image Viewing and Quality

• Pre-Processing: Corrections applied to the digital image before viewing.

  • Line Noise: Voltage variations in the image receptor are corrected.
  • Defective Pixel: Corrected by interpolating adjacent pixel signals.
  • Image Lag: Offset correction is applied to compensate for delayed pixel response.

• Post-Processing: Changes to the image after it is acquired.

  • Annotation: Text labels are added to identify structures.
  • Window/Leveling: Adjust the brightness and contrast of the image.
    • Window Width: Controls contrast (more width = lower contrast).
    • Window Level: Controls brightness (higher level = brighter).
  • Magnification: Zooms in on a region of interest for better visualization of detail.
  • Image Flip: Re-orient the image vertically or horizontally.
  • Image Inversion: Reverses the black and white levels, improving visibility of certain features.
  • Subtraction: Removes portions of the image to enhance specific structures.
    • Used in DSA (Digital Subtraction Angiography).
  • Pixel Shift: Corrects for patient motion during a sequence of images.
  • Region of Interest: Calculates the mean pixel value in a specific area.

Luminance and Image Viewing

• Luminance Intensity: Brightness of the light source (viewbox or monitor).
  • Measured in units of candela per square meter.
• Cosine Law: Viewing a monitor straight on provides the maximum luminance intensity.
  • Viewing from an angle reduces luminance intensity.
• Inverse Square Law: Luminance intensity decreases inversely proportional to the square of the distance from the source.
• LCD Monitors: Utilize a backlight to illuminate each pixel, creating the image.

Digital Image Viewing

• Hard Copy: Film based images viewed on a lightbox.
• Soft Copy: Digital images viewed on a computer monitor.