2-D Ultrasound (US) Transducer (2D-UST) arrays facilitate scan-less volumetric photoacoustic imaging (3D-PAI), but are typically high-cost, involve laborious fabrication process, and permit limited scalability in design with respect to array parameters like element count, aperture size, center frequency ( 𝑓c) and array pitch. In this work, we report a novel, 2-D matrix UST array fabricated on a printed circuit board (PCB) substrate (2D-PCB-UST array) at low-cost and without the need of advanced cleanroom fabrication technologies. Further, the 2D-PCB-UST array parameters can be easily modified with PCB design software. We demonstrate the scalability by fabricating two arrays, (i) an 8×8 array with 1.5 mm pitch and 𝑓c 40 MHz, and (ii) an 4×4 array with 1.2 mm pitch and 𝑓c 11 MHz. Initial characterization results demonstrate wideband PA receive sensitivity, characterized by the 6-dB fractional bandwidth for both low and high frequency UST arrays. Phantom imaging results demonstrate 3D-PAI capabilities despite low element count and sparse array geometry.
Photoacoustic imaging (PAI) is now a very promising imaging technique that provides image with sufficient depth, good resolution, and optical contrast. A conventional PAI system is relatively expensive and mechanically bulky. The study demonstrated that MEMS PMUT achieves miniaturized ultrasound (US) sensor element (either single element or an array of elements) with superior performance in terms of power consumption, flexibility, broader bandwidth, and sensitivity. This implies that these technologically novel qualities hold promise for the use of PMUT as an acoustic sensor in PAI systems in place of the conventional piezoelectric bulk element-based spherical ultrasound (US) transducer. We report our study on the design and development of MEMS PMUT−(central frequency ~ 1MHz) based PAM−that integrates MEMS technology and imaging technology (specifically, photoacoustic imaging (PAI)). In this work, we present a temporal integration of the signals over a certain number (~20) of pulsed light-induced PA waves against the conventional technique to acquire a single 1D PA signals/data corresponding to one individual optical pulse−induced PA waves. This means to say that the enhancement of imaging performance with the use of PMUT acoustic sensor is associated with a reduction of obtainable temporal resolution, i.e., a trade-off exists. With the applied temporal integration method SNR has been improved ~ 20dB. The preliminary study demonstrates that the integration of PMUT in PA imaging modality holds promise as a future (imaging) technology both for biological studies and their applications.
We report on the development of a novel piezo-MEMS-based optofluidic platform to detect the concentration of various species dissolved in a fluid. This platform employs piezoelectric micromachined ultrasound transducers (PMUTs) to work as a photoacoustic receiver, receiving ultrasound from fluid targets present in microfluidic channels while illuminated with a nanosecond pulsed laser. We fabricate both the PMUTs and the microfluidic channels and subsequently use them for the experiment. We also show the capability of PMUTs as a general photoacoustic receiver and demonstrate its signal-to-noise characteristics (~31) and its wide fractional bandwidth (~73%).
We report the development of an opto-acousto-fluidic platform by combining an illumination source in the form of a pulsed laser, a microfluidic channel, and an ultrasound transducer to detect photoacoustic signals generated from the fluid sample inside the channel. We study the effect of the channel dimensions on the emitted acoustic signals using methylene blue solution, a dye of immense interest in processing industry, as a target fluid and select an appropriate channel for further studies. We vary the concentration of the methylene blue dye and collect the corresponding photoacoustic signals. We find that the measured acoustic signal strength varies linearly with the increasing dye concentration, thus making this measurement scheme a potential dye concentration detector. This is a significant finding as it paves the way for developing a miniaturized photoacoustic detector for onsite sensing of dye concentration and perhaps even an online monitoring system which will be radical departure for current analysis methods using bench top bulky and expensive analytical tools.
In this work, we demonstrate the use of parylene C to reduce the ring down time and enhance the fractional bandwidth of a piezoelectric micromachined ultrasound transducer (PMUT). We further study the effect of increase in thickness of parylene C on the vibration response of a PMUT such as the fundamental resonant frequency and the maximum static deflection. It is found that the increase in the thickness of the deposited parylene C film, decreases the quality factor of a PMUT, following a linear trend, with negligible effect on its fundamental resonant frequency. This can be considered to be an important finding as far as the field of ultrasound imaging is concerned, since this technique paves the way to control the axial resolution of the B-mode ultrasound scan by simply tuning a PMUT’s quality factor.
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.
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