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. 2007 Aug;28(8):733-41.
doi: 10.1002/hbm.20303.

Event-related functional near-infrared spectroscopy (fNIRS) based on craniocerebral correlations: reproducibility of activation?

M M Plichta  1 , M J Herrmann, C G Baehne, A-C Ehlis, M M Richter, P Pauli, A J Fallgatter
Affiliations

Event-related functional near-infrared spectroscopy (fNIRS) based on craniocerebral correlations: reproducibility of activation?

M M Plichta et al. Hum Brain Mapp. 2007 Aug.

Abstract

The purpose of the present study was to assess the retest reliability of cortical activation detected by event-related functional near-infrared spectroscopy (fNIRS) based on craniocerebral correlations. Isolated functional activation was evoked in the motor cortex by a periodically performed finger-tapping task. During 44-channel fNIRS recording, 12 subjects performed 30 trials of right and left index finger tapping in two sessions. The retest interval was set to 3 weeks. Simple correlations of the contrast t-values supplemented by scatterplots, channel-wise intraclass correlation coefficients (ICC), as well as reproducibility indices for the size and the location of the detected activation were calculated. The results at the group level showed sufficient single measure ICCs (up to 0.80) and excellent reproducibility of the size and the location (up to 89% were reproducible). Comparisons of the intersession group amplitudes demonstrate that the fNIRS signals were stable across time in a retest study design: the number of significant differences was less than randomly occurring false-positive activated channels if an alpha level of 5% is chosen. Effect size analyses indicated that the intersession amplitude differences are small (mean < 0.25). For deoxyhemoglobin and oxyhemoglobin distinct statistical power profiles were revealed regarding the activation vs. baseline contrast as well as the intersession amplitude differences, indicating a higher sensitivity of deoxyhemoglobin for local hemodynamic changes. The results suggest that sensorimotor activation assessed by event-related fNIRS based on craniocerebral correlations is sufficiently reproducible at the group level.

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Figures

Figure 1
Figure 1
The channel scheme of the probe sets is shown in the middle row/left. Note that only one probe set is displayed (localized over the left hemisphere). Note that the channel numbering of the second probe set over the right hemisphere (not shown) is horizontally mirror‐inverted. Red squares represent light emitters, whereas blue squares are detectors. The region of interest (ROI) is gray shaded. The middle row/center optode is placed over C3/C4 according to the international 10‐20 system as shown in the middle row/right (“localization”). The activation maps are color‐coded t‐values obtained from the group analyses. The measurement sessions are indicated by “t1” and “t2.” Results of O2Hb for right and left finger tapping are shown in the upper panel (“Oxy‐Hb”). The HHb (“Deoxy‐Hb”) results are displayed in the lower panel. Note that the maps are second‐level group maps and based on interpolations from single channels.
Figure 2
Figure 2
A posteriori power analysis of the activation vs. baseline contrasts for O2Hb and HHb (A). The analyses are separated by channels of the predefined ROI and channels outside the ROI (non‐ROI). Given the sample size of n = 12 both NIRS parameters show sufficient statistical power (power >0.80). Note that the alpha level is corrected. B: The effect sizes for the intersession amplitude differences. Statistical power is plotted vs. total sample size given the upper extreme effect size values at the ROI and the non‐ROI level due to randomly occurring intersession amplitude differences. Note that the power analyses for dependent samples are based on an uncorrected alpha level of 0.05.
Figure 3
Figure 3
Scatterplots of the t‐values for O2Hb are shown in A (right finger tapping) and B (left finger tapping). Similarly, the HHb data is shown in C (right finger tapping) and D (left finger tapping). The gray shaded areas represent t‐value ranges of statistical significance. Reproducibility indices are shown in the upper left corner of each scatterplot. Channels that exhibit significant activation are labeled with the channel number (compare to Fig. 1 “probe set”).
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