Short and mid-term reproducibility analysis of cerebral tissue saturation measured by time domain-NIRS

The short- (i.e. over minutes) and mid-term (i.e. over days/weeks) reproducibility of cerebral tissue saturation measured by time domain-NIRS (TD-NIRS) is investigated in this work. We present a pilot study that assess the reproducibility of the measurement of the tissue saturation (StO2) of the prefrontal cortex on a sample of 7 healthy adult volunteers. TDNIRS measurements were acquired at 16 wavelengths, from 780 to 870 nm, in steps of 6 nm, and were fitted with the diffusion model for semi-infinite homogenous media. Then the absolute concentration of oxy- and deoxyhemoglobin ([HbO2], [HHb]) were calculated using Beer-Lambert’s law, in order to calculate the volunteer’s brain tissue saturation (StO2 = [HbO2]/([HbO2]+[HHb])). Three measurement sessions were performed on three different days (within a week interval) to evaluate the mid-term reproducibility of the StO2. For each session, three measurements were taken (within 10 minutes, with repositioning of the probes) to evaluate the short-term reproducibility of the StO2. The reproducibility was expressed as the within-volunteer standard deviation (SDw), calculated using a one-way repeated-measure ANOVA. The SDw in session 1, 2 and 3 were 0.89%, 1.10% and 0.82% respectively, showing a good short-term reproducibility, and the SDw for all 3 sessions was 1.43%, showing a good mid-term reproducibility without significant variations in the StO2 between the 3 sessions. Moreover, the mean ± SD global values of StO2 over all the measurements (n=63) is 62.8+/- 4.2% which is close to the values reported in the literature for adults.