Simultaneous reconstruction of optical absorption property and speed of sound in intravascular photoacoustic tomography

Intravascular photoacoustic tomography (IVPAT) is a newly developed imaging modality for the diagnosis and intervention of coronary artery diseases. It is an ill-posed nonlinear least squares (NLS) problem to recover the absorbed optical energy density (AOED) and optical absorption coefficient (OAC) distribution in the vascular cross sections from pressure photoacoustically generated by tissues with variable speed of sound (SoS). The prior knowledge of the SoS is usually unavailable before IVPAT scanning. The ideal assumption of a constant SoS leads to degraded image quality. This paper focuses on improvement of image quality for IVPAT in tissues with variable SoS by simultaneously recovering the SoS, AOED and OAC from the measured time-dependent pressure series. The joint recovery is implemented by alternately minimizing the errors between the measured and theoretical pressure by forward simulation. The demonstration results indicate that the normalized mean square absolute distance (NMSAD) of the reconstructions produced by this method is decreased by about 15% in comparison to that of the reconstructions with a fixed SoS. Comparison results show that this method outperforms the delay compensation method in recovering the AOED and the two-step algorithm in estimating the OAC by about 20% and 25% in NMSAD respectively.