Coherent Hemodynamics Spectroscopy: A New Technique to Characterize the Dynamics of Blood Perfusion and Oxygenation in Tissue
Hemodynamic-based neuroimaging techniques such as near-infrared spectroscopy (NIRS) and functional magnetic resonance imaging (fMRI) are directly sensitive to the blood volume fraction and oxygen saturation of blood in the probed tissue. The ability to translate such hemodynamic and oxygenation measurements into physiological quantities is critically important to enhance the effectiveness of NIRS and fMRI in a broad range of applications aimed at medical diagnostic or functional assessment. Coherent hemodynamics spectroscopy (CHS) is a novel technique based on the measurement (with techniques such as NIRS or fMRI) and quantitative analysis (with a novel mathematical model) of coherent hemodynamics in living tissues. Methods to induce coherent hemodynamics in humans include controlled perturbations to the mean arterial pressure by paced breathing or by timed inflations of pneumatic cuffs wrapped around the subject’s legs. A mathematical model recently outlined translates coherent hemodynamics into physiological measures of the capillary and venous blood transit times, cerebral autoregulation, and cerebral blood flow. A typical method to analyze the optical signal from non-invasive NIRS measurements of the human brain is the modified Beer-Lambert law (mBLL), which does not allow the discrimination of hemodynamics taking place in the scalp and skull from those occurring in the brain cortex. A hybrid method using continuous wave NIRS (with the mBLL) together with frequency-domain NIRS (with a two-layer diffusion model) was successfully used to discriminate oscillatory hemodynamics in the superficial (extracerebral) tissue layer from that in deeper, cerebral tissue.
KeywordsNear-infrared spectroscopy Diffuse optics Functional imaging Hemodynamics Autoregulation Cerebral blood flow
This research is supported by the US National Institutes of Health (Grants no. R01-NS095334 and R21-EB020347).
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