Abstract
Quantitative photoacoustic tomography (QPAT) employing a light propagation model will play an important role in medical diagnoses by quantifying the concentration of hemoglobin or a contrast agent. However, QPAT by the light propagation model with the three-dimensional (3D) radiative transfer equation (RTE) requires a huge computational load in the iterative forward calculations involved in the updating process to reconstruct the absorption coefficient. The approximations of the light propagation improve the efficiency of the image reconstruction for the QPAT. In this study, we compared the 3D/two-dimensional (2D) photon diffusion equation (PDE) approximating 3D RTE with the Monte Carlo simulation based on 3D RTE. Then, the errors in a 2D PDE-based linearized image reconstruction caused by the approximations were quantitatively demonstrated and discussed in the numerical simulations. It was clearly observed that the approximations affected the reconstructed absorption coefficient. The 2D PDE-based linearized algorithm succeeded in the image reconstruction of the region with a large absorption coefficient in the 3D phantom. The value reconstructed in the phantom experiment agreed with that in the numerical simulation, so that it was validated that the numerical simulation of the image reconstruction predicted the relationship between the true absorption coefficient of the target in the 3D medium and the reconstructed value with the 2D PDE-based linearized algorithm. Moreover, the the true absorption coefficient in 3D medium was estimated from the 2D reconstructed image on the basis of the prediction by the numerical simulation. The estimation was successful in the phantom experiment, although some limitations were revealed.
Highlights
Photoacoustic (PA) imaging [1,2,3] noninvasively provides physiological information such as hemodynamics in micro blood vessels
The value reconstructed in the phantom experiment agreed with that in the numerical simulation, so that it was validated that the numerical simulation of the image reconstruction predicted the relationship between the true absorption coefficient of the target in the 3D medium and the reconstructed value with the 2D photon diffusion equation (PDE)-based linearized algorithm
Htarg was linearly related to the PA pressure wave, and the differences in Htarg could cause the errors in the image reconstruction
Summary
Photoacoustic (PA) imaging [1,2,3] noninvasively provides physiological information such as hemodynamics in micro blood vessels. By employing the light propagation model described by the radiative transfer equation (RTE) or the photon diffusion equation (PDE) [4,5,6,7], the PA image of the light absorption coefficient can be reconstructed quantitatively. This technique is referred to as quantitative PA tomography (QPAT) [8]. QPAT reconstructing the absorption coefficient will be useful in medical diagnoses
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