Technical Performance Assessment of Digital Whole Slide Imaging Systems in Anatomic Pathology

What You Need to Know? 👇

What are the key components that must be characterized in a digital pathology WSI system submission?

WSI systems require characterization of 11 main components: slide feeder, light source, imaging optics, mechanical scanner movement, digital imaging sensor, image processing software, image composition, image file formats, image review manipulation software, computer environment, and display. Each component needs specific technical specifications and test methods.

How should color reproducibility be assessed in digital pathology systems?

Color reproducibility testing requires using target slides with measurable color patches similar to stained tissue, including grayscale ramps. The truth of color patches must be measured separately, then compared with intended colors and actual display output to evaluate accuracy and precision of color transformation throughout the imaging chain.

What system-level tests are required beyond component-level characterization?

Five key system-level assessments are required: color reproducibility, spatial resolution, focusing quality, whole slide tissue coverage, and stitching error evaluation. These tests assess composite performance of multiple components and capture interactions that component-level testing cannot adequately evaluate.

What human factors validation testing is needed for WSI systems?

Human factors validation must demonstrate that representative users can perform essential and safety-critical tasks under simulated use conditions. Testing should include all known use-related errors from similar devices, consider user fatigue, and evaluate the complete user interface including software menus, physical controls, and information displays.

How should turnaround time performance be evaluated and reported?

Turnaround time measurement starts when users enter commands and ends when images are completely updated on display. Sponsors must report typical turnaround times along with test methods and conditions, considering variations due to user operations, image content, data size, computer workload, and display specifications.

What quality control procedures must be established for WSI systems?

Quality control procedures must include frequency and testing methods for laboratory technologists and field engineers with quantitative action limits. Testing should cover slide feeder, scanning mechanisms, tissue coverage, bar code reader, light source, imaging sensor, and calibrations at both component and system levels.

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What You Need to Do 👇

Recommended Actions

1. Develop comprehensive technical documentation covering all components and systems
2. Implement testing protocols for:
   • Component level performance
   • System level performance
   • Color reproducibility
   • Spatial resolution
   • Focus quality
   • Tissue coverage
   • Stitching accuracy
3. Conduct human factors validation testing:
   • Define user populations
   • Identify critical tasks
   • Create simulated use conditions
   • Document results
4. Establish quality control procedures:
   • Define testing methods
   • Set quantitative action limits
   • Create quality control manual
5. Prepare complete labeling package:
   • Instructions for use
   • Service instructions
   • Warnings
   • Training materials
6. Document risk management:
   • Identify hazards
   • Assess risks
   • Implement controls
   • Monitor effectiveness
7. Validate software components:
   • Image processing
   • Image review
   • Quality control
   • System performance

Key Considerations

Non-clinical testing

• Component level testing for each part of the imaging chain (slide feeder, light source, optics, scanner, sensor, etc.)
• System level testing including:
  • Color reproducibility assessment
  • Spatial resolution evaluation
  • Focus quality testing
  • Whole slide tissue coverage verification
  • Stitching error assessment
  • Turnaround time measurement

Human Factors

• Human factors/usability validation testing required
• Test with representative users under simulated conditions
• Evaluate critical tasks and use scenarios
• Consider user capabilities, expectations and fatigue
• Assess workstation ergonomics and environmental factors

Software

• Image processing software requirements
• Image review manipulation software capabilities
• Quality control procedures and testing methods
• Software validation according to FDA guidance

Labeling

• Must satisfy 21 CFR Part 801 and 21 CFR 809.10
• Include detailed instructions for use, servicing, warnings
• Labeling studies separate from usability testing
• Final version required for validation testing

Safety

• Risk analysis and management required
• Use-related hazards identification
• Risk mitigation strategies
• Quality control procedures

Other considerations

• Computer environment specifications
• Display requirements and testing
• System performance metrics
• Turnaround time assessment

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Relevant Guidances 🔗

• Applying Human Factors Engineering and Usability Engineering to Medical Devices
• Content of Premarket Submissions for Device Software Functions
• Use of ISO 10993-1 for Biological Evaluation and Testing of Medical Devices
• Design Controls for Medical Device Manufacturers

Related references and norms 📂

• ISO 14971:2007: Medical Devices – Application of Risk Management to Medical Devices
• AAMI/ANSI HE75:2009: Human Factors Engineering – Design of Medical Devices
• IEC 62366-1:2015: Medical devices – Application of usability engineering to medical devices
• ISO 12233:2014(E): Photography — Electronic still picture imaging — Resolution and spatial frequency responses
• ISO 8039:2014: Optics and optical instruments — Microscopes — Magnification
• ISO 13653:1996: Optics and optical instruments – General optical test methods
• ISO 9039:2008: Optics and photonics — Quality evaluation of optical systems
• ISO 15795:2002: Optics and optical instruments — Quality evaluation of optical systems
• ISO 230-2:2014: Test code for machine tools —Part 2: Determination of accuracy and repeatability

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Original guidance

• Technical Performance Assessment of Digital Whole Slide Imaging Systems in Anatomic Pathology
• HTML / PDF
• Issue date: 2016-04-20
• Last changed date: 2019-03-28
• Status: FINAL
• Official FDA topics: Medical Devices, Laboratory Tests, 510(k), Labeling, Premarket, IVDs (In Vitro Diagnostic Devices)
• ReguVirta ID: abd3a98d61a40e71105bd7d42e397cad