Photoacoustic imaging (PAI) is a hybrid imaging modality that uses ultrasound waves generated from light absorbing tissue chromophores to provide high spatial resolution and depth-resolved molecular information. However, conventional PAI setups involve complicated arrangement of optical components surrounding opaque ultrasound transducers to achieve a co-aligned optical illumination and ultrasound receiving field. This opacity of traditional ultrasound transducers impedes the miniaturization of the imaging head, besides precluding integration with other imaging modalities. To overcome these limitations, we recently fabricated a single element transparent ultrasound transducer (TUT) window using indium tin oxide (ITO) coated lithium niobate (LiNbO3) piezoelectric material and demonstrated its application for endoscopy and microscopy PAI applications. Extending on this work, we report new developments of TUTs to improve their detection bandwidth, sensitivity, and signal to noise ratio (SNR) while maintaining sufficient transparency. This includes investigating LiNbO3 and PMN-PT as transparent piezoelectric materials with different matching layer designs. Fabricated TUTs were characterized using pulse echo and electrical impedance analysis. The PAI performance of the fabricated TUTs were characterized using photoacoustic A-line signals from light absorbing targets. The proposed TUTs are low cost, easy to fabricate, and can be scaled and easily integrated into different PAI geometries such as: endoscopy, microscopy, and computed tomography systems for high-throughput imaging applications.
Infant brain imaging is highly challenging but necessary for diagnosing various prevalent disorders including vascular malformations, encephalitis, and abusive head trauma. Conventional brain imaging technologies such as MRI, CT, and PET are not suitable for repeated use on neonates due to the use of ionizing radiation (CT and PET), need for patient transport, uncomfortable environment, high cost, and bulky equipment. A wearable photoacoustic imaging (PAI) hat can be an ideal candidate for this application. However, its practical realization suffers from many system design problems such as complex assembly, unviability of full-hat rotation around the neonatal head, ultrasound coupling, and requirements of <3,000 ultrasound data acquisition channels to cover the whole brain. Here, we present a modular photoacoustic imaging (PAI) hat solution that uses an innovative modular design approach, making it realizable by assembling individual working units while minimizing the challenges of back-end electronics. The modular photoacoustic hat consists of multiple PAI disc modules of 2 inches in diameter that conform to the shape of the local head surface and assembled on a hat to cover the whole neonatal brain. Each PAI disc is integrated with optical fibers for light excitation of brain tissue. For photoacoustic detection, the discs are either densely packed with ultrasound elements to eliminate the need for rotation or can have fewer ultrasound elements (usually in trapezoidal shape) on the rotating disc to overcome large number of data acquisition channels. In this article, we have demonstrated the design, integration and initial results of the proposed wearable PAI-hat.