Lecture Notes: Unit 15b - Resolution Number Four: Spatial and Contrast Resolution

Overview

• Focus on spatial and contrast resolution.
• Emphasizes importance of resolution as accuracy (space, time, contrast).
• Covers basics, with more concepts to be discussed later.

Key Points

• Spatial Resolution: Machine's ability to correctly display anatomical detail.

  • Sometimes called detail resolution.
  • Includes axial, lateral, and elevational scanning planes.
  • Affected by:
    • Line density, pixel density.
    • Gain adjustments.
    • Spatial and frequency compounding.
    • Magnification type (right vs read).
  • Transducer and frequency choice are crucial.
  • High frequencies and proper gain settings improve spatial resolution.

• Contrast Resolution: System's ability to display different grays.

  • Important for seeing borders between structures.
  • Tied to the system's scan converter and bits per pixel.
  • Current systems display 256 shades of gray (8 bits).
  • Human eyes limited to seeing 30-64 shades.
  • Improved by reducing dynamic range, making subtle differences more visible.
  • Reducing dynamic range compresses 256 shades into fewer, more distinguishable shades for human eyes.

Visual Examples

• Soft Tissue Phantom: Demonstrates varying echogenicities and contrast resolution.
• Ultrasound Images:
  • High dynamic range image (70) vs low dynamic range image (30).
  • Lower dynamic range shows better contrast, more defined borders.

Conclusion

• No activities or checks included in this section.
• This lecture serves as a summary of spatial and contrast resolution.
• More details to be added in future units, particularly on Doppler effects.

Important Concepts to Remember

• Always consider how choices like transducer type and gain setting affect resolution.
• Reducing dynamic range can significantly enhance contrast resolution.
• Understanding and manipulating these resolutions is key to accurate ultrasonic imaging.