Reliable Fast (20 Hz) Acquisition Rate by a TD fNIRS Device: Brain Resting-State Oscillation Studies

Figures

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  Figure 1. TD NIRS device scheme. λ = wavelength, PMT = Photomultiplier tube, TCSPC = Time-correlated single photon counting, D = Detection channel, Sync = Synchronization signal.

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  Figure 2. Typical acquisition window during an instrument response function (IRF) measurement. RED = 689 nm, IR = 828 nm, FWHM = Full width at half maximum, semi-logarithmic scale.

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  Figure 3. Averaged reduced scattering coefficient (μs′, (a)) and absorption coefficient (μa, (b)) over 10 repetitions and relative error bars, for different count rates. Red: RED wavelength, blue: IR wavelength. The dashed lines are the average μs′ and μa retrieved for counts from 0.5 to 4 × 106. The green and black lines represent the 1% and 3% error regions, respectively.

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  Figure 4. Absorption (μa) and reduced scattering (μs′) coefficients for both wavelengths as function of the acquisition time. Initial count rate set at 2 × 106 counts/s (a) or 7 × 106 counts/s (b). The horizontal lines represent the average value over the acquisitions at 1, 0.1 and 0.05 s.

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  Figure 5. Number of photons/s for the RED wavelength, collected on solid phantoms for different values of absorption (labels 2, 4, 6 and 8: 0.07, 0. 21, 0.35, 0,49 cm−1, respectively) and reduced scattering (series A, B, C and D: 5, 10, 15 and 20 cm−1, respectively) with different source-detector distances ρ (different colors). In the figure, the count rate necessary to obtain a CV < 1% is shown as well.

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  Figure 6. Probe placement during the in vivo occlusion on the arm muscle.

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  Figure 7. Hemodynamic parameters during an arterial arm occlusion. The dashed vertical lines indicate the start and the end of the occlusion period. The different lines represent the different source-detector distances (from 2 to 5 cm). (a) Oxyhemoglobin (O2Hb). (b) Deoxyhemoglobin (HHb).

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  Figure 8. Time courses of the concentration of the cortical O2Hb and HHb, after subtraction of the average over the initial 5 s.

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  Figure 9. Power spectrum of the cortical O2Hb (red) and HHb (blue) hemoglobin for 5 min’s resting-state acquisition on the motor cortex. In the inset, a zoomed-in view of the frequencies ≤ 0.5 Hz is shown. LFO: Low frequency oscillation; VLFO: Very low frequency oscillation.