New near-infrared spectroscopy method for local measurements of cerebral blood flow

Abstract

Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that is sensitive to blood volume, blood flow, and oxygen consumption in biological tissue. In particular, a NIRS-measured quantity that has been previously considered as a surrogate for blood flow measurements is the difference of oxy- and deoxy-hemoglobin concentrations ([HbD] = [HbO2] – [Hb]). We propose a new NIRS method for measurements of cerebral blood flow (CBF), which improves on the [HbD] surrogate by accounting for blood volume contributions and for temporal delays due to the blood transit time in the microvasculature. This new NIRS method relies on concepts of coherent hemodynamics spectroscopy (CHS), and we identify it with the acronym NIRS-CHS. We report a comparison of CBF transient dynamics measured on human subjects with NIRS-CHS, with the [HbD] surrogate and with diffuse correlation spectroscopy (DCS). We found a good agreement between the CBF dynamics measured with NIRS-CHS and with DCS, while the [HbD] dynamics lag because of the delayed effect of CBF on [HbD] due to the capillary and venous blood transit times. The NIRS-CHS method also affords absolute measurements of baseline CBF, for which we found a value of 69 ± 6 ml/100g/min (mean ± standard error) in a group of six healthy volunteers. Further studies to characterize and validate CBF measurements with NIRS-CHS are currently ongoing, with an emphasis on the assessment of accuracy, precision, and reproducibility.