Impact of Photoacoustic Source Location on Flexible Array Curvature Estimation with a Maximum Lag-One Spatial Coherence Metric

One key component to accurate photoacoustic image reconstruction with flexible array transducers is knowledge of element positions as the flexible array shape varies. Our previously proposed metric calculates the maximum lag-one spatial coherence (mLOC) of a photoacoustic target, with demonstrated advantages to estimate the curvature of a flexible array. However, the effectiveness of mLOC in relation to target locations remained unclear. Therefore, we investigated mLOC performance across different source locations by first designing a radial grid consisting of 20 simulated photoacoustic sources at varying azimuthal angles and depths. The accuracy of the mLOC-estimated array radius was 97.59%-100% when compared with the ground truth curvature. Signals from deeper sources produced greater coherence when beamforming images with the correctly estimated array radius. In addition, we introduced a normalized full-width at half-prominence (nFWHP) metric to assess the flatness of the mLOC measurements as a function of estimated array radius, demonstrating greater mLOC effectiveness with estimating flexible array radii with decreasing distance between the source and the transducer center. Therefore, the photoacoustic source should be placed as close to the array radius center as possible to achieve the best array shape estimation results with mLOC.