Bundled-Optode Method in Functional Near-Infrared Spectroscopy

<div><p>In this paper, a theory for detection of the absolute concentrations of oxy-hemoglobin (HbO) and deoxy-hemoglobin (HbR) from hemodynamic responses using a bundled-optode configuration in functional near-infrared spectroscopy (fNIRS) is proposed. The proposed method is then applied to the identification of two fingers (i.e., little and thumb) during their flexion and extension. This experiment involves a continuous-wave-type dual-wavelength (760 and 830 nm) fNIRS and five healthy male subjects. The active brain locations of two finger movements are identified based on the analysis of the <i>t</i>- and <i>p</i>-values of the averaged HbOs, which are quite distinctive. Our experimental results, furthermore, revealed that the hemodynamic responses of two-finger movements are different: The mean, peak, and time-to-peak of little finger movements are higher than those of thumb movements. It is noteworthy that the developed method can be extended to 3-dimensional fNIRS imaging.</p></div

Comparison of two approaches for an inactive channel (Ch. 30, Subject 5).

<p>(a) HbOs computed by the MBLL approach (thin blue: raw, thick red: low-pass filtered); (b) HbOs by the proposed method; (c)-(d) the averaged HbO across 5 trials in (a) and (b), respectively, for little finger; (e)-(f) the averaged HbO for thumb finger.</p

Brain regions of fingers directly detected by electrocorticogram in the motor cortex (blue dashed rectangle), see Fig 9 in [41].

<p>Brain regions of fingers directly detected by electrocorticogram in the motor cortex (blue dashed rectangle), see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0165146#pone.0165146.g009" target="_blank">Fig 9</a> in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0165146#pone.0165146.ref041" target="_blank">41</a>].</p

Comparison of parameters of HRs of little and thumb finger movements.

<p>Comparison of parameters of HRs of little and thumb finger movements.</p

An example showing that the MBLL method cannot tell but the proposed method can tell (Ch. 33, Subject 5).

<p>(a) HbOs computed by the conventional MBLL method (blue thin curve: raw data, red thick curve: low-passed filtered); (b) HbOs obtained by the proposed method: In this case, the channel will be judged inactive by the MBLL method, while it will be judged active by the proposed method.</p

Optode arrangement on the left motor cortex for detection of right-finger movements.

<p>Squares and circles are emitters and detectors, respectively, and C₃ denotes the reference point from the International 10–20 System.</p

Comparison of the CNRs of HbOs in 48 channels (Subject 5).

<p>(a) The CNR of little movements; (b) the CNR of thumb movements: Red bars are the CNRs of HbOs computed by the conventional MBLL method whereas blue bars indicate the CNRs of those calculated by the proposed approach.</p

Comparison of the HbOs computed by the conventional MBLL method and the bundled-optode approach (Ch. 20, Subject 5, blue thin curves: raw data, red thick curves: low-passed filtered).

<p>(a) HbOs computed by the MBLL approach; (b) HbOs computed by the proposed method; (c)-(d) the averaged HbOs of the little finger movements (averaged over trials 1, 4, 6, 7, and 9) in (a)-(b), respectively; (e)-(f) the averaged HbOs of the thumb finger movements (averaged over trials 2, 3, 5, 8, and 10) in (a)-(b), respectively; the boundaries in (c)-(f) denote one standard deviation.</p

Bundled-optode arrangement.

<p><b>(</b>a) Concept of bundled-optode arrangement; (b) 1-emitter and 7-detector configuration for HbO/HbR measurement (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0165146#pone.0165146.g002" target="_blank">Fig 2</a> for their assignments): Optode <i>1</i> (square) is emitter and optode <i>2</i> and optodes <i>3</i>~<i>8</i> are short- and long-separation detectors (circles), respectively.</p

Illustration of the baseline-correction method (Ch. 14, Subject 5).

<p>(a) An HbO signal before applying the baseline-correction method (blue thin curve) and the fitted signal <i>f</i>(<i>x</i>) (red thick curve); (b) the corrected HbO signal (blue thick curve).</p