Dynamic acoustic focusing in photoacoustic transmitter

Photoacoustic imaging plus X: a review

Significance

Photoacoustic (PA) imaging (PAI) represents an emerging modality within the realm of biomedical imaging technology. It seamlessly blends the wealth of optical contrast with the remarkable depth of penetration offered by ultrasound. These distinctive features of PAI hold tremendous potential for various applications, including early cancer detection, functional imaging, hybrid imaging, monitoring ablation therapy, and providing guidance during surgical procedures. The synergy between PAI and other cutting-edge technologies not only enhances its capabilities but also propels it toward broader clinical applicability.

Aim

The integration of PAI with advanced technology for PA signal detection, signal processing, image reconstruction, hybrid imaging, and clinical applications has significantly bolstered the capabilities of PAI. This review endeavor contributes to a deeper comprehension of how the synergy between PAI and other advanced technologies can lead to improved applications.

Approach

An examination of the evolving research frontiers in PAI, integrated with other advanced technologies, reveals six key categories named "PAI plus X." These categories encompass a range of topics, including but not limited to PAI plus treatment, PAI plus circuits design, PAI plus accurate positioning system, PAI plus fast scanning systems, PAI plus ultrasound sensors, PAI plus advanced laser sources, PAI plus deep learning, and PAI plus other imaging modalities.

Results

After conducting a comprehensive review of the existing literature and research on PAI integrated with other technologies, various proposals have emerged to advance the development of PAI plus X. These proposals aim to enhance system hardware, improve imaging quality, and address clinical challenges effectively.

Conclusions

The progression of innovative and sophisticated approaches within each category of PAI plus X is positioned to drive significant advancements in both the development of PAI technology and its clinical applications. Furthermore, PAI not only has the potential to integrate with the above-mentioned technologies but also to broaden its applications even further.

Dual-modality fibre optic probe for simultaneous ablation and ultrasound imaging

All-optical ultrasound (OpUS) is an emerging high resolution imaging paradigm utilising optical fibres. This allows both therapeutic and imaging modalities to be integrated into devices with dimensions small enough for minimally invasive surgical applications. Here we report a dual-modality fibre optic probe that synchronously performs laser ablation and real-time all-optical ultrasound imaging for ablation monitoring. The device comprises three optical fibres: one each for transmission and reception of ultrasound, and one for the delivery of laser light for ablation. The total device diameter is < 1 mm. Ablation monitoring was carried out on porcine liver and heart tissue ex vivo with ablation depth tracked using all-optical M-mode ultrasound imaging and lesion boundary identification using a segmentation algorithm. Ablation depths up to 2.1 mm were visualised with a good correspondence between the ultrasound depth measurements and visual inspection of the lesions using stereomicroscopy. This work demonstrates the potential for OpUS probes to guide minimally invasive ablation procedures in real time.

Laser-induced ultrasound transmitters for large-volume ultrasound tomography

We present a protocol for the design, fabrication and characterisation of laser-induced ultrasound transmitters with a specific, user-defined frequency response for the purpose of ultrasound tomography of large-volume biomedical samples. Using an analytic solution to the photoacoustic equation and measurements of the optical and acoustic properties of the materials used in the transmitters, we arrive at a required mixture of carbon black and polydimethylsiloxane to achieve the desired frequency response. After an in-depth explanation of the fabrication and characterisation approaches we show the performance of the fabricated transmitter, which has a centre frequency of 0.9 MHz, 200% bandwidth and 45.8 ∘ opening angle, multi-kPa pressures over a large depth range in water.

Binary amplitude switch for photoacoustic transducer toward dynamic spatial acoustic field modulation

Photoacoustic (PA) transducers are an attractive method of producing high-amplitude, high-frequency, broad-bandwidth ultrasound signals with excellent immunity to electromagnetic interference, when compared with their traditional electroacoustic counterparts. However, the lack of effective control over the spatial sound field prohibits PA transducer technology from further widespread application. This paper presents the first, to the best of our knowledge, experimental study on the dynamic spatial ultrasound modulation strategy for the use of PA transducers, in which a novel PA transducer element is designed. This consists of a suspended compound PA conversion film, whose backing condition can be switched between air and glass through pneumatic actuation to create destructive and constructive acoustic wave interference, respectively. As a result, nearly an order of magnitude contrast in the output acoustic amplitude can be obtained by switching the device's backing condition given the same laser excitation, thus achieving a binary amplitude tuning. Furthermore, a linear PA transducer array consisting of three independently controllable elements is used for a proof-of-concept demonstration of the dynamic spatial sound field manipulation. To the best of the authors' knowledge, this is the first time that such a unique capability has been successfully applied to PA transducer technology.

High-Frequency 0.36BiScO3-0.64PbTiO3 Ultrasonic Transducer for High-Temperature Imaging Application

( 1- x )BiScO₃- x PbTiO₃ (BS-PT) ceramics have excellent piezoelectricity and high Curie temperature at its morphotropic phase boundary (MPB) ( x = 0.64 ), so it is a promising piezoelectric material for fabricating high-temperature ultrasonic transducer (HTUT). Electric properties of 0.36BS-0.64PT ceramics were characterized at different temperatures, and an HTUT with the center frequency of about 15 MHz was designed by PiezoCAD based on the measuring results. The prepared HTUT was tested in a silicone oil bath at different temperatures systematically. The test results show that the HTUT can maintain a stable electrical resonance until 290 °C and get a clear echo response until 250 °C with slight changes of the center frequency. Then, a stepped metal block submerged in silicone oil was imaged by the HTUT until 250 °C. Velocity of silicone oil and axial resolution of the HTUT at different temperatures was calculated. The results verify the capability of 0.36BS-0.64PT-based HTUT for high-temperature ultrasonic imaging applications.

Lead halide perovskite for efficient optoacoustic conversion and application toward high-resolution ultrasound imaging

Lead halide perovskites have exhibited excellent performance in solar cells, LEDs and detectors. Thermal properties of perovskites, such as heat capacity and thermal conductivity, have rarely been studied and corresponding devices have barely been explored. Considering the high absorption coefficient (104~105 cm-1), low specific heat capacity (296-326 J kg-1 K-1) and small thermal diffusion coefficient (0.145 mm2 s-1), herein we showcase the successful use of perovskite in optoacoustic transducers. The theoretically calculated phonon spectrum shows that the overlap of optical phonons and acoustic phonons leads to the up-conversion of acoustic phonons, and thus results in experimentally measured low thermal diffusion coefficient. The assembled device of PDMS/MAPbI3/PDMS simultaneously achieves broad bandwidths (-6 dB bandwidth: 40.8 MHz; central frequency: 29.2 MHz), and high conversion efficiency (2.97 × 10-2), while all these parameters are the record values for optoacoustic transducers. We also fabricate miniatured devices by assembling perovskite film onto fibers, and clearly resolve the fine structure of fisheyes, which demonstrates the strong competitiveness of perovskite based optoacoustic transducers for ultrasound imaging.

Air-backed photoacoustic transmitter for significantly improving negative acoustic pressure output

Aiming to pursue an ultrasound signal with a significantly improved negative acoustic pressure level, which is one of the critical characteristics for exciting the ultrasound cavitation effect, a real applicable air-backed photoacoustic transmitter is presented. Different from the conventional solution of relying on a complicated focusing structure design, it works based on an acoustic signal phase reversal and amplitude superposition strategy. By using an innovative sandwich-like suspending photoacoustic layer with optimized structure design, the initial backward-propagating positive sound pressure can be converted into the forward-propagating negative one efficiently. For proof-of-concept demonstration, photoacoustic transmitter prototypes adopting a polydimethylsiloxane (PDMS)/candle soot nanoparticle/PDMS-PDMS composite as a photoacoustic conversion layer were fabricated and characterized. From experiment results, an acoustic signal with a remarkable ratio of negative pressure level to a positive one of 1.3 was successfully realized, which is the largest value ever reported, to the best of our knowledge. Moreover, when compared to the commonly used glass and PDMS-backing conditions in the photoacoustic area, nearly 200% and 400% enhancements in negative pressure output were achieved, respectively.