Reconstruction of the optical absorption coefficient from photoacoustic signals measured by scanning coaxial probe with regularization methods

Reconstruction of the absorption coefficient from photoacoustic signals is discussed. The photoacoustic (PA) signals were acquired by using a ring-shaped P(VDF-TrFE) acoustic sensor coaxially arranged with an optical fiber. The acoustic sensor scanned the measured object. The linearized image reconstruction method previously presented by the authors was modified for the measurement with the coaxial probe. The distribution of the absorption coefficient was reconstructed by solving the inverse problem based on the PA wave equation and the photon diffusion equation. The linearized forward model was formulated by solving the partial differential equations with finite element method. To eliminate the effect of the unknown background on the PA signal, the differences between the PA signals measured at different positions were used for the image reconstruction. The image reconstruction method was validated by numerical and phantom experiments. Moreover, the reconstructed images with the Tikhonov and l(p) sparsity regularization methods were compared from the standpoints of spatial resolution, robustness to noise and quantification of the absorption coefficient.