Absolute measurement of absorption coefficient by combining photoacoustics and acousto-optics

Quantitative measurements of the chromophores concentration in vivo present a challenge in photoacoustic imaging. The obtained signal depends on the absorbed optical density which is the product of absorption coefficient and local fluence. As a result of wavelength-dependent optical attenuation and scattering, the local fluence in biological media varies with depth and the optical wavelength. This fluence heterogeneity needs to be compensating in the order to recover the absolute absorption coefficient. In this paper we describe a new approach to recover the absolute optical absorption coefficient from measured PA signals based in combination between photoacoustic and acousto-optic signals. The present method is based on two principles, a given photon trajectory through a scattering medium can be travelled in two directions with equal probability and photons which traverse a certain volume can be labeled in that volume with the use of focused ultrasound. We give proof of the principle using Monte Carlo simulation and we demonstrate the experimental feasibility of the technique in tissue-mimicking phantom by correcting a fluence heterogeneity caused by the optical diffusion.