Design of a dual frequency probe for photoacoustic imaging of the carotid artery

A dual frequency probe using a multi-layer piezoelectric material is proposed for simultaneous ultrasound and photoacoustic imaging of the carotid artery with a high resolution ultrasound and a high sensitivity photoacoustic image. The probe consists of lead zirconate titanate (PZT) for ultrasound stack and and polyvinylidene difluoride (PVDF) array for photoacoustic signal reception, which is placed on top of the PZT stack. We used 3D finite element analysis to evaluate a quarter of the full aperture of the dual frequency array, having 48 elements diced PZT-5H for ultrasound pulse-echo and 16 elements of 28µm thick, kerfless PVDF for photoacoustic receiving. We showed that considering the PVDF array as the second matching layer of the ultrasound stack minimized its loading effect at the cost of operating in a higher operation frequency of 9.9 MHz. We modeled a design with and without sub-dicing, where sub-dicing and subsequent suppression of lateral modes allows larger elements and thus larger aperture. The -3dB bandwidth of the ultrasound stack with and without sub-dicing are 87% and 75% relative to the center frequencies. We found a transmit sensitivity of 17 kPa/V and 21 kPa/V for those two realizations respectively.