Improved approach to extract absorption coefficient from photoacoustic signal for photoacoustic spectroscopy

Previous studies on measurements of hemoglobin concentrations and oxygen saturations of human blood by pbotoacoustic spectroscopy assume that the exponential attenuation of the optical radiation in blood results in photoacoustic signals with exponential temporal profiles and absorption coefficients could be extracted by fitting exponential functions. In this paper, we demonstrate that the detected photoacoustic signals are the convolutions of the optical absorption distributions in samples, and the first derivative of the temporal profile of the excitation laser, and the impulse response of the ultrasound detector. The detected photoacoustic signals from absorbers with exponential optical absorption distributions do not keep exponential profiles. In addition, we present an improved approach to calculate the absorption coefficient by fitting the detected photoacoustic signal with a function that is the convolution of an exponential function, and the first derivative of the temporal profile of the laser, and the impulse response of the detector. This approach is validated by both numerical simulations and experimental results.