Low-Cost Scalable PCB-Based 2-D Transducer Arrays for Volumetric Photoacoustic Imaging

Photoacoustic (PA) imaging provides deep tissue molecular imaging of chromophores with optical absorption contrast and ultrasonic resolution. Present PA imaging techniques are predominantly limited to one 2-D plane per acquisition. The 2-D ultrasound (US) transducers, required for real-time 3-D PA imaging, are high cost, complex to fabricate, and have limited scalability in design. We present novel printed circuit board (PCB)-based 2-D matrix US transducer arrays that are capable of being bulk manufactured at low cost without using laborious US fabrication tools. The 2-D US array specifications are easily scalable with respect to widely available PCB design tools. To demonstrate scalability, we fabricated low-frequency (11 MHz) $8\times8$ matrix array and high-frequency (40 MHz) $4\times4$ matrix array by directly bonding an undiced polyvinylidene difluoride (PVDF) piezoelectric material of desired thickness to the custom designed PCB substrate. Characterization results demonstrate wideband PA receive sensitivity for both the low-frequency (6-dB bandwidth: 87%) and the high-frequency (6-dB bandwidth: 188%) arrays. Volumetric PA imaging results of light-absorbing targets inside optical scattering medium demonstrate improved spatial resolution and field of view (FOV) with an increase in aperture size.