Performance assessment and ISO/IEC standards in fNIRS and cerebral oximetry

Heidrun Wabnitz, Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany

Antonio Pifferi, Politecnico di Milano – Dipartimento di Fisica, Milan, Italy

Duration: 90 min

Capacity: 90

Level: Introductory


Requirements: None

Synopsis: Recently, ISO/IEC standards have been developed for fNIRS equipment and cerebral tissue oximeters. While theses international consensus standards are of great importance for developers, manufacturers and users of the technology, little is known about them in the scientific community. We present the current status, future activities, the process of development and how to participate. 
Performance assessment of devices – as part of the existing standards and beyond – is the main focus of this minicourse. The fNIRS standard contains several performance tests based on a phantom with variable attenuation. On the other hand, multi-laboratory, multi-national efforts have been undertaken in collaborative research projects to characterize and compare NIRS instrumentation, with the aim to facilitate development and clinical application as well as quality assurance. Several of these concepts and protocols (MEDPHOT and nEUROPt) covering a variety of phantom-based tests can be helpful to characterize commercial fNIRS devices as well as instrumentation under development and can augment the tests in the fNIRS standard.

In cerebral oximetry, accuracy and comparability of tissue oxygenation measured by different devices are still an issue. Scientific efforts are in progress to establish a recognized phantom-based assessment of accuracy to eliminate the need of invasive human desaturation studies. State-of-the-art “tissue hemoglobin phantoms” are homogeneous liquid turbid phantoms that contain hemoglobin which can be oxygenated and deoxygenated. Alternative phantom concepts and future developments will be discussed as well.

Course structure:

  1. Status of ISO/IEC standardization in fNIRS and cerebral oximetry
    • Family of standards for medical electrical equipment
    • Relevance of performance assessment
    • Process of development, future activities and the role of experts
      • IEC/ISO 80601-2-71:2015 fNIRS equipment (currently under revision)
      • ISO/IEC 80601-2-85:2021 cerebral tissue oximeter equipment
  2. Performance assessment in fNIRS
    • Phantom tests in the fNIRS standard
    • Phantoms and protocols for more comprehensive performance assessment of fNIRS devices
      • Introduction to MEDPHOT, BIP and nEUROPt protocols
      • Applicability of selected tests for fNIRS performance assessment
        (e.g. responsivity, contrast, contrast-to-noise ratio, depth selectivity)
    • Other approaches
    • Multi-laboratory initiatives for performance assessment and phantom characterization
  3. Performance assessment in cerebral oximetry
    • Principle of cerebral oximeters
    • Traditional in-vivo validation
    • Role of phantoms for evaluation of accuracy of tissue oxygenation in the standard for cerebral oximeters
      • Tissue hemoglobin phantom
      • Phantom vs. in-vivo testing
    • Further development and alternative phantom concepts

Learning objectives:

  • Which specific ISO/IEC standards exist for fNIRS devices and cerebral oximeters
  • Who develops them, how to participate
  • Which methods of performance assessment of devices are contained in the standards
  • Which other methods exist and can be applied for characterizing device performance
  • Which are the multi-laboratory initiatives on performance assessment in diffuse optics
  • Which types of phantoms are used for performance assessment
  • What are the directions of further development of phantoms, methods for performance assessment and international standards in the field of NIRS

Overall, the minicourse aims at fostering the culture of performance assessment and standardization in the fNIRS community.