Event-related functional near-infrared spectroscopy (fNIRS): Are the measurements reliable?

The purpose of the present study was to investigate the retest reliability of event-related functional near-infrared spectroscopy (fNIRS). Therefore, isolated functional activation was evoked in the occipital cortex by a periodic checkerboard stimulation. During a 52-channel fNIRS recording, 12 subjects underwent 60 trials of visual stimulation in two sessions. The retest interval was set to 3 weeks. Linear correlations of the contrast t values supplemented by scatter plots, channel-wise intraclass correlation coefficients (ICC) as well as reproducibility indices for the quantity of activated channels (R-QUANTITY) and the location (R-OVERLAP) of the detected activation were calculated. The results at the group level showed good reliability in terms of the single measure ICCs (up to 0.84) and excellent reproducibility quantified by R-QUANTITY and R-OVERLAP (up to 96% of the quantity and the location were reproducible), whereas the results at the single subjects' level were mediocre. Furthermore, the reliability assessed by single measurement ICCs improved if regarded at a cluster level. (c) 2005 Elsevier Inc. All rights reserved.