1 July 2010 Phasor representation of oxy- and deoxyhemoglobin concentrations: what is the meaning of out-of-phase oscillations as measured by near-infrared spectroscopy?
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J. of Biomedical Optics, 15(4), 040512 (2010). doi:10.1117/1.3483466
Abstract
We propose a phasor representation for oscillations at a given frequency (or relatively narrow frequency band) of hemoglobin concentrations in tissue, as well as hemoglobin concentrations measured by near-infrared spectroscopy. This representation provides a straightforward visualization of the phase relationships between oscillations of oxy-, deoxy-, and total hemoglobin concentrations ([HbO], [Hb], and [HbT], respectively). We observe that measured oscillations of [Hb] and [HbO] with a phase difference that is neither 0 nor must result from the combination of different physiological processes that are out of phase (or time shifted) with respect to each other. Finally, we propose the use of cross-correlation phasors to map phase relationships and correlation levels among hemoglobin oscillations measured at spatially distinct locations at a given frequency. Such a representation may find a natural application in the study of functional connectivity networks in the brain.
Feng Zheng, Angelo Sassaroli, Sergio Fantini, "Phasor representation of oxy- and deoxyhemoglobin concentrations: what is the meaning of out-of-phase oscillations as measured by near-infrared spectroscopy?," Journal of Biomedical Optics 15(4), 040512 (1 July 2010). http://dx.doi.org/10.1117/1.3483466
Submission: Received ; Accepted
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KEYWORDS
Tissues

Tissue optics

Near infrared spectroscopy

Phase shifts

Absorption

Phase measurement

Brain activation

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