Headset Exoskeleton

The exoskeleton can be used for children from 4 years old to Adult.

The exoskeleton weight is from 386g (8/8 version) to 669g (in 16/32-EEG version) + the Blackout cap (241g).

Hair is a major limitation of the fNIRS technic. Indeed, hair absorbs both RED and IR wavelenghts, even more with dark and dense hair than bright and thin one. One major advantage of the MedelOpt headset is to provide a direct access to the hair and scalp. This alllow a better removal of hair below optodes.

Hardware

Depending on the fNIRS style version, sampling frequency can be set from 4 Hz up to 32 Hz. EEG sampling freq is fixed at 512 Hz.

Yes, we are able to stream data online to third party software through the Medelopt API.

Data are logged on the MiniPC directly. Further to the acquisition, data text files can be either retrieved or transfered via SD Card, Cloud, USB, etc.

Markers will be send to the electronic (PCB) card and thus both modalities will get it simultaneously.

EEG and fNIRS are recorded by the same Hardware and Software system. EEG recording triggers the fNIRS recording, which enables a perfect synchronization of the data. There is no need to re-synchronized the data with software layers such as LSL (Lab Stream Layer) or afterwords during post-processing.

Channels and Montage

A certain amount of bundles (Sources or Detectors) is provided depending on the product. The system can be upgraded later on, by adding more bundles. Full configuration consists in 16 sources and 32 detectors (plus 8 EEG). The number of sources-detectors necessary for one project depends on the scientific hypothesis, experimental protocol, and optodes montage design.

In term of fNIRS modality, the standard distance will be within the range of 2 to 4cm for a medium to long channel. For the short channel, the agreed distance within the scientific community is 0.84cm for adult.

The paired calibration has to be done based on the ‘NIRS check’ tab. For a good calibration and to avoid ligth saturation, we recommend using the detector with the highest signal for a given source (i.e. highest signal).

The localization of the optodes can be done in relation to the International EEG system (e.g. 10-5 or 10-20). This gives the “anatomical” standard labels for comparison between studies/subjects. Digitizing the optodes localisation relatively to each participant’s head is advised to ensure more robustness of the results and to limit inter-subjects variability in the analysis.

We are provided a pre-digitized headset with 82 sensor locations (whole head positions) i.e. you can then make your own montage. You will then have to adjust and control the position of the holder on the exoskeleton according to Nasion-Inion & LpA/LpR measurements. The exoskeleton owns some measurement tools.

If you want to use its own montage with different location than the pre-digitized, it can build it according to needs and similarly, check that the sensors are appropriately placed on each participant.

Data and processing

Raw EEG, fNIRS, as well as settings information are provided in a text file format. Only raw data are provided, meaning that no filter is applied (for EEG and fNIRS). and ligth intensities are provided for fNIRS. A conversion tool is available to convert text file in .EDF format (EEG) and .NIRS (fNIRS)

No. ElOpt is only for recording purpose. Post-processing can be done with any OpenSource software used by the fNIRS community (Homer3, NIRStoolbox, Fieldtrip, MNEPython).

Converting concentrations can be done by clicking on the run icon in Homer3 if the processing pipeline includes the functions : (1) intensities to optical densities and (2) optical densities to concentrations. These functions are included in the default pipeline provided by Homer3.

MedelOpt use case and other modalities compatibilities

Medelopt® device is NOT sold as a medical device and thus it is NOT INTENDED for use as a treatment of disease or clinical diagnosis. Use of Medelopt® requires IRB (Institutional Review Board) or equivalent approval prior to initiating any acquisition on human subjects.

No, the MedelOpt system is not compatible with MRI.

We have never tested the MedelOpt headset with a transcranial Doppler headset. In principle it should be feasible, but still needs to be tested. Customized service can be provided, needs to be further discussed.

Our system is compatible with TMS. However, we/the researcher might have to adapt the optical LED/DET if they want to record around the coil. Also, we/the researcher may design something to help fixing the coil to the headset if necessary. But this should be done specifically for each project /coil size, etc. Test are in progress.

For angiography, the MedelOpt electronic board should be protected to avoid any perturbation due to X-Rays. We haven’t tested it yet, but it could be interesting to investigate depending on the customers needs.

EEG

Yes, EEG electrodes are AG/AGcL electrodes with gel to optimise the Signal-To-Noise ratio.

MedelOpt provides 8 electrodes + 1 reference + 1 ear clip used as the ground. You can have thus a maximum of 8 EEG channels. All EEG electrodes are Ag/AgCl cupules that need conductive gel to enable a good signal quality.

Reference is placed on Cz on the demo montage and this is a common reference for all EEG channels. As the reference electrode design is similar to the others medelopt EEG electrodes, the reference electrode position on the scalp can be changed. Note that the reference can be changed online in ElOpt, in the “EEG check” tab. However, it will lead to 1 EEG channel loss as the electrode will be used as the reference. We advise to change the reference offline, during the post-processing of the EEG data.