Improving axial resolution uniformity in deep-tissue optoacoustic imaging via entropy-driven design of dual-frequency...

Dual-frequency or multi-frequency transducers have been proposed to balance deep penetration and high resolution in optoacoustic (OA) imaging, based on the well-established tradeoff that low frequencies provide deeper penetration, while high frequencies offer higher resolution. In practice, conventional transducer designs are primarily guided by the signal's center frequency and bandwidth, as these parameters fundamentally constrain spatial resolution. However, such criteria alone are insufficient, as they overlook the influence of transducer geometry within the array. To address this limitation, we introduce k-space analysis and a weighted entropy (WE) metric that links transducer design parameters to directional resolution performance. Simulations and phantom experiments validated that the dual-frequency multi-segment transducer array (DF-MSTA), combining 3 and 7.5 MHz, achieved more uniform and enhanced axial resolution (by up to 23.8 %), compared to a single-frequency MSTA operating at 7.5 MHz. The results align with predictions from the k-space analysis and WE quantification. This work provides a transducer design strategy that jointly considers frequency selection and array geometry, along with a quantitative framework to optimize axial resolution in deep-tissue OA imaging, offering insights beyond conventional approaches.