Phantom for standardization in functional near-infrared spectroscopy, part 1: implementation and usage

The use of functional near-infrared spectroscopy (fNIRS) is expanding, including examples of devices approved for routine clinical use for specific indications. Instrument standardization is a critical element to facilitate clinical adoption. Currently, there is no published description of a phantom that meets the requirements of IEC 80601-2-71, the IEC/ISO standard for fNIRS equipment.

We report an example of the implementation of the fNIRS standard phantom described in IEC 80601-2-71. We further report results from measurement campaigns with this phantom prototype in Japan and Europe.

A phantom prototype was built and circulated among multiple academic and commercial fNIRS groups with diverse instrumentation. The phantom prototype was characterized by wavelength-dependent measurements of its diffuse optical features and utilized in a test for fNIRS signal magnitude as described in IEC 80601-2-71.

The optical loss of this phantom prototype as well as its change by varying an internal aperture were found to be $\sim 40\mathrm{dB}$ and between 3.5 and 3.6 dB, respectively. The test for fNIRS signal magnitude based on this phantom was successfully carried out on various commercial fNIRS devices.

The characteristics of the phantom prototype agreed with the specifications in the standard. The phantom prototype proved suitable for the related test in IEC 80601-2-71.