Quantitative evaluation of the relative contribution ratio of cerebral tissue to near-infrared signals in the adult human head: a preliminary study

Abstract

Combining spatially- and time-resolved spectroscopies. we attempted to quantitatively evaluate the contribution ratio of the partial mean pathlength of cerebral tissue to the observed overall mean pathlength, in which haemoglobin concentrations were selectively changed by administration of acetazolamide. When acetazolamide was administered, the observed increases in oxygenated haemoglobin depended on the probe distance, which became progressively larger at distances of 2, 3 and 4 cm. Increases in oxygen saturation were detected at 3 and 4 cm spacing, but not at 2 cm. Assuming that the modified Lambert-Beer's law can exist in the inhomogeneous structure of the head, then, we could estimate the contribution ratio of the cerebral tissue to optical signals at the probe distances of 2, 3 and 4 cm as 33%, 55% and 69%, respectively. Using these values, we recalculated acetazolamide-induced concentration changes in oxygenated-haemoglobin in the cerebral tissue, which resulted in the same values at distances of 2, 3 and 4 cm as expected. Thus, our present method opened the door to the possibility of selectively obtaining optical signals attributed to cerebral tissue.

Cerebral functional imaging using near-infrared spectroscopy during repeated performances of motor rehabilitation tasks tested on healthy subjects

“…fNIRS signals from Ch1 with 6.0 mm source-detector distance are supposed to reflect hemodynamic activity confined within the scalp, whereas fNIRS signals from the extra-scalp layers, such as the brain, gradually increase in channels with larger source-detector distance (i.e., Ch 2–5) (Kohri et al, 2002). That is, fNIRS signals in channels with larger source-detector distances include both hemodynamic responses in the scalp and other layers, including the brain.…”

Illuminating the Black Box: Investigating Prefrontal Cortical Hemodynamics during Exercise with Near-Infrared Spectroscopy

“…The geometries of the sulci and the boundary between the gray and white matter layers were shown to have a negligible effect on the optical path length. More recently, Kohri et al (2002) reported that, in human heads in vivo, the estimated contribution of cerebral tissue to optical signals increased from 33% to 55-69% as the interoptode distance increased from 2 cm to 3 cm to 4 cm. Other in vivo investigations, using scalp ischemia and cerebral oligemia (reduction of blood supply) to manipulate extraand intracerebral hemodynamics independently, have reached similar conclusions (Germon, Kane, Manara, & Nelson, 1994;Germon et al, 1998Germon et al, , 1999.…”

Near-infrared spectroscopy determined cerebral oxygenation with eliminated skin blood flow in young males

“…Importantly, we could identify the The some studies indicate that the optical paths length and the sensitivity to surface layer oxygenation are influenced by the source-detector distance [38,39]. Kohri et al [40] reported that the contribution of cerebral tissue to optical signals were related to the source-detector distance (20 mm; 33 %, 30 mm; 55 %, 40 mm; 69 %), indicating that increasing the detector distance increases effective optical path length within brain tissue. However, there is a large variation in individual correction factor (Table 2), indicating that the effect of the source-detector distance (15 vs. 30 mm) on the contribution of cerebral tissue to optical signals varied widely in each subject.…”