Volumetric pulse echo and optoacoustic imaging by elaborating a weighted synthetic aperture technique

Integrating the ultrasonic pulse-echo (PE) and optoacousic (OA) imaging is a potent approach in rendering the volumetric images of biological tissues. The deliverable information are essentially uncorrelated but highly complementary in learning about the optical and mechanical properties of the medium. Yet, owing to the inhomogeneities in acoustic velocity and the optical scattering, this synergistic approach suffers from the low depth resolution, low contrast and artifacts like off-axis contributions and phase distortion. In this work, an adaptive weighted dynamic focusing based reconstruction technique namely, weighted synthetic aperture (WSA), has been developed to address the aforementioned defects, in particular for annular array. Our findings show the efficiency of WSA method in 3D reconstruction of simulated phantom. We elaborate WSA to estimate the spatial location, size, reflectivity function and absorption coefficient of the insonified/illuminated targets for both imaging modalities. The phase distortion introduced by the separable delay approximation is addressed with an adaptive weighting factor that combines coherence factor (CF) and phase coherence factor (PCF). In addition, the weighting factor incorporates the spatial impulse response (SIR), which is associated with the properties of the transducer in order to inverse the effect of the transducer on imaging quality. Using numerical phantom, the simulation results demonstrate that incorporating SIR into the weighting factor ensures the isotropic sensitivity while CF and PCF are suppressing the artifacts, grating lobe and phase aberration for both OA and PE images.