Joint reconstruction of multiple initial pressures and the speed of sound in photoacoustic tomography

The aim of the photoacoustic tomography (PAT) inverse problem is to reconstruct the initial pressure distribution from measured ultrasound waves generated by absorption of externally induced pulse of near-infrared light. Image reconstruction calls for modelling of these acoustic pressure waves, and thus knowledge of the speed of sound distribution of the target is required. However, the speed of sound is often unknown in practical situations, and therefore it would be valuable to reconstruct it together with the initial pressure. In addition, the speed of sound can provide interesting quantitative information of the imaged target. In this work, joint reconstruction of the initial pressure and speed of sound in PAT is studied. We propose an approach where photoacoustic measurements are performed using multiple different initial pressure distributions that are generated to the target using illuminations from different directions. Methodology for joint reconstruction of these multiple initial pressure and speed of sound distributions is formulated. The methodogy was evaluated with numerical simulations. The results show that, utilising data generated by producing multiple initial pressures in the target, initial pressure distributions can be reconstructed more accurately with less artefacts compared to a reference approach of utilising a single light illumination.

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