2021 SfNIRS Virtual Meeting Q&A: fNIRS standards special session

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mari
mari (@mari)
Admin
6 days ago

To Alessandro: Iso standards exist for CW-Nirs, is anything done to include other modalities like FD TD DCS SCOS etc?

Torricelli
Torricelli (@torricelli)
Reply to  mari
6 days ago

The -71 standard for fNIRS device uses light attenuation as parameter. A discussion to extend it also to TD (using the integral of the DTOF) and to FD (using the DC signal) took place in the work-group but the decision was to limit the standard to CW since that parameter was not able to capture the specificity of TD and FD device. Work is in progress to find a better solution for testing also FD and TD devices.

mari
mari (@mari)
Admin
6 days ago

To Alessandro: in page 10 you had DCS sensitivity to recover absorption and scattering, how were they measured? Should we propose phantoms for blood flow assessment? What are the possible stable phantoms for that?

Torricelli
Torricelli (@torricelli)
Reply to  mari
6 days ago

That was a TD DCS system if I am not wrong (able to recover both optical properties and blood flow index).. Unfortunately for DCS and blood flow we do not have a clear solution for a stable phantom.

mari
mari (@mari)
Admin
6 days ago

To Felix: you said rest time should not be a multiple of Mayer wave. Is that .1 Hz in everybody?

Felix Scholkmann
Felix Scholkmann (@felix)
Admin
Reply to  mari
6 days ago

More or less. According to m experience, if there is a spontanous oscillation in this freuqency range it is often at about 0.1 Hz – the Mayer wave frequency. The amplitude varies for each subject.

Ilias Tachtsidis
Ilias Tachtsidis (@i-tachtsidisucl-ac-uk)
6 days ago

To Luca: thanks for summarising all the available software packages, databases, file formats etc. Are we at a stage to “demand” a file standard to be followed when it come to fNIRS studies and how can we make sure that people/industry implements it?

Luca Pollonini
Luca Pollonini (@lpolloni)
Editor
Reply to  Ilias Tachtsidis
6 days ago

I think we are there, Ilias. Once BIDS is fully approved and converters are fully developed validated, I believe that we should make a big push towards embracing these formats fully. From my own experience with manufacturers, adhering to standards is an incentive to keep them competitive, so hopefully won’t be a challenge to get them onboard.

mari
mari (@mari)
Admin
6 days ago

To Felix: combining CW and FD NIRS but with FD only in the forehead, is that sufficient? how big and how to correct for local differences in skull thickness and vascularization?

Felix Scholkmann
Felix Scholkmann (@felix)
Admin
Reply to  mari
6 days ago

Sure, a whole head coverage with both would be better. But FD at the PFC gives you absolute values (at least for one or to ROI) which is a nice additional information.

CulverJoseph
CulverJoseph (@culverjoseph)
6 days ago

To Felix: Echo Mari’s question about Mayer Waves…. my impression is that frequency changes with the subject, making it difficult to design around. What do you think is more important – staying away from multiples of 0.1 hz, or to jitter the timing?

Felix Scholkmann
Felix Scholkmann (@felix)
Admin
Reply to  CulverJoseph
6 days ago

Sure, it’s a complicated issue. In my experience, when there is a strong spontaneous oscillation present in the low-frequency range it often has indeed a peak aorund the Mayer wave frequency. We tried to avoid multipes of 0.1 in our study designs (at least we had the feedling that it helps to avoid this interference issue). Jitter the timing is also important. We use both.
Would be great to investigate this in more detail with a new study …

Ilias Tachtsidis
Ilias Tachtsidis (@i-tachtsidisucl-ac-uk)
6 days ago

To Alessandro: Do we have a single solid phantom to give to every fNIRS equipment manufacturer and tell\ask\demand them for your system to comply as an fNIRS neuroimaging system your instrument should be able to measure these phantom properties? and considering most of the manufactured equipment are CW instruments what this phantom should look like?

Torricelli
Torricelli (@torricelli)
Reply to  Ilias Tachtsidis
6 days ago

To my knowledge the best solution today is the dynamic switchable phantom (Pifferi et al. J. Biomed Opt 20:121304 (2015)) but so far we have tested it only with TD systems and maybe 1 FD and 1 CW system. Work is in progress in the so called “phantom group” of experts supporting the IEC/ISO joint workgroup. If you are interested to join the “phantom group” just email me.

CulverJoseph
CulverJoseph (@culverjoseph)
6 days ago

Meryem,
On statistical significance. In fMRI, packages like SPM leverage the concept of clusters in images to strengthen the statistical analysis of functional images. Basically, big clusters have higher statistical significance than small blobs (for the same t-value). What are your thoughts on these cluster methods in fNIRS…. how much of this is being done, problems unique to fNIRS?

FortiRodrigo
FortiRodrigo (@fortirodrigo)
6 days ago

Regarding the performance assessment protocols, such as the MEDPHOT/NEUROpt/BitMap. Are there are any available methods/recipes to make the solid phantoms in a reproducible manner? Also, are there any standard methods to calibrate these phantoms before testing a new system?

Torricelli
Torricelli (@torricelli)
Reply to  FortiRodrigo
6 days ago

Making a phantom is quite easy (e.g. just mix epoxy resin, TiO2 powder, and black toner in proper amounts). Making a good phantom can be kind of art (just like cooking good food). For the first phantoms I made, I used no tools (apart for a scale), but nowadays we have mechanical stirrer, vacuum pump, oven. That helps a lot reproducibility.For calibration we use our time domain NIRS setup and look for optical properties over a broad wavelength range and in different location.

Andrés Fabián Quiroga Soto
Andrés Fabián Quiroga Soto (@aquiroga)
6 days ago

Thanks for the talk! What are the most serious problems of non-standardization in hardware development, data formats, and methodological procedures? And How does this impact the fNIRS publications?

Torricelli
Torricelli (@torricelli)
Reply to  Andrés Fabián Quiroga Soto
6 days ago

For the hardware development, testing the device with calibrated phantoms will give you indication on possible instability of the system (short term or long term), on the effect of noise on your signal, on linearity )or non linearity) in the measured signal. Better testing all these items before moving to in vivo tests (to save a lot of time in analyzing bad data, and also for ethical reasons).

Luca Pollonini
Luca Pollonini (@lpolloni)
Editor
Reply to  Andrés Fabián Quiroga Soto
6 days ago

I guess there are different elements to this:
1) Lack of hardware and methods: As I mentioned, I think it is healthy to keep working on improving these aspects, and probably do not want to “stop the clock” on any of that;
2) Data formats: not sharing data may ultimately affect the visibility of your publication, and standardizing formats helps sharing