Quantification of optical absorption coefficients from acoustic spectra with photoacoustic tomography

Optical absorption is closely associated with many physiologically important parameters, such as the concentration and oxygen saturation of hemoglobin, and it can be used to quantify the concentrations of non-fluorescent molecules. We introduce a method to quantify the absolute optical absorption based upon the acoustic spectra of photoacoustic (PA) signals. This method is self-calibrating and thus insensitive to variations in optical fluence. Factors such as the detection system bandwidth and acoustic attenuation can affect the quantification but can be canceled by measuring the acoustic spectra at two optical wavelengths. This method has been implemented on various PA systems, including optical-resolution PA microscopy, acoustic-resolution PA microscopy, and reconstruction based PA array systems. We quantified the optical absorption coefficients of phantom samples at various wavelengths. We also quantified the oxygen saturation of hemoglobin in live mice.