Overview
This lecture reviews the core concepts of spatial and contrast resolution in ultrasound imaging, emphasizing their definitions, influences, and how sonographers can optimize them for accurate anatomical images.
Spatial Resolution
- Spatial resolution refers to the machine's ability to display anatomical detail accurately (also called detail resolution).
- It includes three scanning planes: axial, lateral, and elevational resolution.
- Spatial resolution is affected by both transducer characteristics and machine tools/settings.
- Sonographers can influence spatial resolution by adjusting line density, gain, using spatial or frequency compounding, and choosing right magnification.
- High-frequency transducers and appropriate focus placement improve spatial resolution.
- A thin ultrasound beam and short pulses enhance image accuracy.
- Transducer and frequency choices are critical for maximizing spatial resolution.
Contrast Resolution
- Contrast resolution is the system's ability to display different gray levels and distinguish borders between anatomical structures.
- It is primarily system-dependent, influenced by the scan converter and bits per pixel.
- Most modern systems use 8 bits per pixel, displaying up to 256 shades of gray.
- Human eyes can typically distinguish only about 30–64 shades of gray.
- Reducing dynamic range compresses gray scale to a level perceivable by the human eye, improving contrast resolution.
- Lower dynamic range makes borders more distinct, aiding in soft tissue differentiation.
- High dynamic range images look more uniformly gray; lower dynamic range enhances contrast and visible detail.
Key Terms & Definitions
- Spatial Resolution — The ability to accurately display anatomical detail in the correct location.
- Axial/Lateral/Elevational Resolution — Resolution in different scanning planes determined by transducer and beam properties.
- Contrast Resolution — The ability of a system to distinguish between differences in echo intensity (gray levels).
- Dynamic Range — The range of grays displayed; reducing it enhances visible contrast.
- Scan Converter — The part of the ultrasound machine assigning memory (bits) to each pixel, affecting gray scale display.
Action Items / Next Steps
- Prepare for an upcoming unit on dynamic range and its detailed role in imaging.
- Review key concepts of spatial and contrast resolution as a foundation for Doppler imaging topics.