Frequency-Domain Photoacoustic Phase Spectroscopy: A Fluence-Independent Approach for Quantitative Probing of Hemoglobin Oxygen Saturation

In this paper, it is shown that the phase of the frequency-domain photoacoustic (PA) signal can be used to measure the absorption coefficient (μ
_α
) of the chromophore. This method can be referred to as a calibration-free approach in the sense that it is not affected by the attenuation of fluence in the tissue. This helps to enhance the accuracy of quantitative PA functional imaging. However, the premise for employing the aforementioned method is that chromophore geometry should be known a priori. As a proof of applicability of the theory, the method was applied to a simplified geometry and the extension of the method to more complicated geometries is discussed. One of the key subjects of functional imaging in medicine is blood. Parameters such as total hemoglobin concentration and hemoglobin oxygen saturation are valuable for diagnostics as well as for treatment of many diseases. The developed method was employed for in vitro monitoring of blood oxygenation on heparinized sheep blood and is applicable to characterization problems in biological tissues and other turbid media.