Embodiments of the invention pertain to methods for imaging a light absorption coefficient distribution. Embod iments of the subject method can be implemented without knowing the strength of incident light in advance and without requiring careful calibrations in the non-scattering medium. Embodiments of the method can combine conventional photoacoustic tomography (PAT) with diffusing light measurements coupled with an optimization procedure based on the photon diffusion equation. Images of absorbing targets as small as 0.5mm in diameter embedded in a 50mm diameter background medium can be quantitatively recov ered. Small targets with various optical contrast levels relative to the background can be detected well. Embodiments of the subject reconstruction method can include first obtaining the map of absorbed optical energy density. Embodiments can obtain the map of absorbed optical energy density through a model-based reconstruction algorithm that is based on a finite element solution to the photoacoustic wave equation in frequency domain subject to the radiation or absorbing boundary conditions (BCs). The distribution of optical fluence can then be obtained. Embodiments can obtain the distribution of optical fluence using the photon diffusion equa tion based optimization procedure. The distribution of optical absorption coefficient can then be recovered from the distribution of optical fluence and the absorbed energy density.