Iterative reconstruction method for photoacoustic section imaging with integrating cylindrical detectors

Photoacoustic imaging of cross-sectional slices of extended objects requires ultrasound detectors equipped with an acoustic cylindrical lens rotating around the imaged object. The finite width of the sensor and the small focal depth of lenses with large aperture lead to various imaging artifacts. In this study, these artifacts are on the one hand avoided by the special design of the sensor and on the other hand by a model based, iterative reconstruction algorithm. The integrating property of the cylindrical detector, which exceeds in direction of the cylinder axis the size of the imaged object, avoids the lateral blurring that normally would result from the finite width of a small detector. In addition, an iterative algorithm is presented based on the system matrix that models the signal generation of the device. With this algorithm the imperfect focusing properties of the lens, especially for parts of the object moving out of focus during the rotational scan, are corrected. A direct reconstruction from the measured signals, which in case of the integrating sensor uses the inverse Radon transform, is compared to the reconstruction after iterations, both in a simulation and an experiment. A significant improvement of resolution perpendicular to the section is observed.