Accuracy and Limitations
Accuracy and Limitations
HeartLab provides tools for performing measurements on medical images received from external systems (for example imaging modalities or vendor-neutral archives). The accuracy of these measurements depends on multiple clinical and technical factors, including image quality, display conditions, and user interaction.
Measurement quality is not determined solely by the software. It is influenced by image acquisition, image visualisation, and operator technique. Final clinical interpretation and reporting always remain the responsibility of the reporting clinician.
Key Factors Affecting Measurement Accuracy
1. Image Quality
Measurement accuracy begins with the quality of the source image. Factors that may influence image quality include:
- Patient positioning and fixation
- Patient or organ motion
- Imaging modality and acquisition protocol
- Reconstruction artefacts or distortions
- Spatial and contrast resolution
High-quality image acquisition is essential for reliable measurements. Poor image quality directly reduces measurement precision and diagnostic confidence.
2. Display and Viewing Conditions
The way images are displayed in HeartLab affects how accurately anatomy can be interpreted and measured.
Important display settings include:
- Zoom level
- Grey level and contrast
- Window width and level
- Screen resolution
These settings influence how clearly anatomical boundaries are visualised and how precisely measurement points can be placed.
3. Operator Interaction and Point Placement
The most significant factor affecting measurement accuracy is the user’s ability to correctly place points or contours.
- Measurements rely on manual placement of points on anatomical structures
- Accuracy depends on how precisely the cursor is positioned
- Clear identification of anatomical boundaries is essential
Users must determine whether the selected points accurately represent the intended anatomy.
Technical Accuracy Considerations
Cursor Positioning and Pixel Resolution
Cursor placement is limited by the physical resolution of the display.
- The cursor can only be positioned at the level of screen pixels
- This introduces a positioning uncertainty of approximately ± half a screen pixel
If the screen pixel size is δ mm, the positional uncertainty is approximately:
± 0.5 × δ mm
Impact of Zoom
Zoom level directly affects measurement precision.
- Zooming in improves precision by reducing relative positioning uncertainty
- Zooming out increases uncertainty because cursor movement becomes less precise relative to image detail
For best results, images should be zoomed so that image pixels appear larger than screen pixels, allowing more precise point placement.
Measurement and Error Propagation
All measurements (distance, area, volume, and derived calculations) are calculated from user-placed points. Any uncertainty in point placement propagates into calculated values.
Examples of affected measurements include:
- Distance
- Angle
- Area
- Volume
- Derived calculations (for example ejection fraction)
Practical Guidance for Clinicians
To improve measurement accuracy in daily practice:
- Use the highest-quality image or frame available
- Zoom in before placing critical measurement points
- Ensure anatomical borders are clearly visible before tracing
- Verify contours across multiple frames where appropriate
- Repeat measurements if image quality or border definition is poor
- Document any limitations when image quality affects diagnostic confidence
Interpretation and Responsibility
HeartLab provides measurement tools and calculated values based on user input. However:
- Measurements depend on image quality and operator technique
- Technical limitations (such as pixel resolution and zoom level) influence precision
- Clinical interpretation and final reporting remain the responsibility of the clinician