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TECHNOLOGY

Data Quality

Products designed by our engineers meet stringent quality and safety criteria. Below we present selected signal samples from our products based on standard signal quality measurement methods.

Finger Tapping

Finger Tapping Task is commonly used in validation studies of fNIRS temporal resolution (Drenckhahn et al., 2015).

This example shows a simple single-subject finger tapping experiment, where the participant was asked to perform finger-to-thumb movements with the right hand as fast as possible. The subject was asked to perform the following sequence:

2 — 3 — 4 — 5 — 5 — 4 — 3 — 2, where
2 – index finger,
3 – middle finger,
4 – ring finger,
5 – little finger.

There were 8 repetitions of the task with 20 seconds of the task itself and 43 seconds of rest periods between them. This is a measurement for a single channel localized between C3 (source) and CP3 (detector) optode positions.

Single-trial hemodynamic response over the left motor cortex area

Fig 1. The time traces of oxy- (red line) and deoxyhemoglobin (blue line) across eight repetitions of the right-hand finger tapping task (yellow boxes) and rest period (white boxes) at C3-CP3 channel position.

8-trial average HRF

Fig. 2. The hemodynamic average response during right-hand finger tapping task (yellow box) and rest condition (white box). The signal over the left motor area (Source: C3; Detector: CP3) shows increased oxy-Hb (red line) and decreased deoxy-Hb (blue line), interpreted as the activation of this area.

Single-trial hemodynamic response over the left motor cortex area

Fig 1. The time traces of oxy- (red line) and deoxyhemoglobin (blue line) across eight repetitions of the right-hand finger tapping task (yellow boxes) and rest period (white boxes) at C3-CP3 channel position.

8-trial average HRF

Fig. 2. The hemodynamic average response during right-hand finger tapping task (yellow box) and rest condition (white box). The signal over the left motor area (Source: C3; Detector: CP3) shows increased oxy-Hb (red line) and decreased deoxy-Hb (blue line), interpreted as the activation of this area.

Motor Imagery

Motor imagery is defined as the mental simulation of a movement without any real action. Mental representation of a right hand movement evokes higher activation of motor cortex areas located on the opposite side of the head (contralateral) and lower activation of areas located on the same side (ipsilateral) (Fig. 3.). In the case of the BOLD response measured by fNIRS, greater activation corresponds to increased oxyhemoglobin levels and a decrease in deoxyhemoglobin levels. Our study results present a difference in the motor cortex activations registered in both hemispheres during imagined and real right-hand movement (Fig. 4.).

Fig 3. Localization of the fNIRS sources (red) and detectors (blue).

Fig. 4. The hemodynamic average (n=4) response during movement imagery and execution of right-hand movement over contralateral (left) and ipsilateral (right) motor cortices. Channel over the left-hemisphere (S7-D3) show increased oxy-Hb and decreased deoxy-Hb, interpreted as the activation of this area. A similar but smaller response has been observed on the opposite side of the head (S8-D4).

Fig. 4. The hemodynamic average (n=4) response during movement imagery and execution of right-hand movement over contralateral (left) and ipsilateral (right) motor cortices. Channel over the left-hemisphere (S7-D3) show increased oxy-Hb and decreased deoxy-Hb, interpreted as the activation of this area. A similar but smaller response has been observed on the opposite side of the head (S8-D4).

Fig 3. Localization of the fNIRS sources (red) and detectors (blue).

Fig. 4. The hemodynamic average (n=4) response during movement imagery and execution of right-hand movement over contralateral (left) and ipsilateral (right) motor cortices. Channel over the left-hemisphere (S7-D3) show increased oxy-Hb and decreased deoxy-Hb, interpreted as the activation of this area. A similar but smaller response has been observed on the opposite side of the head (S8-D4).

Fig. 4. The hemodynamic average (n=4) response during movement imagery and execution of right-hand movement over contralateral (left) and ipsilateral (right) motor cortices. Channel over the left-hemisphere (S7-D3) show increased oxy-Hb and decreased deoxy-Hb, interpreted as the activation of this area. A similar but smaller response has been observed on the opposite side of the head (S8-D4).

Signal quality during motion conditions

The notable advantage of fNIRS technology is its increased resistance to environmental artifacts compared to other brain recording methods. However, movements of the entire body, specific body parts (such as head movements), or shifts of the optodes on the scalp during recording can still affect signal quality.

To demonstrate the impact of these factors on data quality, we conducted a study (n = 10) involving finger-tapping and relaxation sequences under four different experimental conditions:

  1. sitting;
  2. walking on a treadmill;
  3. riding an exercise bike; and
  4. sitting with shifting optodes and significant head movements.

 

The folder in BIDS (Brain Imaging Data Structure) format contains .snirf files from a group of 10 participants involved in the experiment. The markers indicate the moments when artifacts occurred in the signal, as well as the experimental conditions (see Fig. 7). During the experiment, data were collected from 50 channels, which included 4 short channels, distributed bilaterally over the motor cortex, as well as in the frontal and occipital regions (see Fig. 8).

Fig. 6. Experimental procedure.

Fig. 7. List of markers: LEFT - left-hand finger tapping; RIGHT - right-hand finger tapping.

Fig.8. Optodes positions. The digit above the channel indicates the number of files in the data set where the channel has obtained a Scalp Coupling Index above 0.80.

Fig. 9. The group-averaged time course of changes in hemoglobin concentration (solid line - HbO; dashed line - HbR) during finger tapping of the left and right hands. The signal was averaged for channels over the motor cortex located on the contralateral side relative to the movement being performed. The standard deviation is marked in semi-transparent color.

SIGNAL QUALITY AND DATA SAMPLES

Source-detector separation distances for up to 60 mm

Fig. 5A

Fig 5. The figure shows raw signal for source-detector separation distances of 40 mm (fig.5A), 50mm (fig.5B) and 60 mm (fig.5C). Fig. 5D shows a filtered signal (15-sample median filter) for source-detector separation of 60 mm.

Fig. 5B

Fig 5. The figure shows raw signal for source-detector separation distances of 40 mm (fig.5A), 50mm (fig.5B) and 60 mm (fig.5C). Fig. 5D shows a filtered signal (15-sample median filter) for source-detector separation of 60 mm.

Fig. 5C

Fig 5. The figure shows raw signal for source-detector separation distances of 40 mm (fig.5A), 50mm (fig.5B) and 60 mm (fig.5C). Fig. 5D shows a filtered signal (15-sample median filter) for source-detector separation of 60 mm.

Fig. 5D

Fig 5. The figure shows raw signal for source-detector separation distances of 40 mm (fig.5A), 50mm (fig.5B) and 60 mm (fig.5C). Fig. 5D shows a filtered signal (15-sample median filter) for source-detector separation of 60 mm.

Sample Raw Data

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