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Acoustic resolution photoacoustic micros- copy (AR-PAM) can achieve deeper imaging depth in biological tissue, with the sacrifice of imaging resolution compared with optical resolution photoacoustic microscopy (OR-PAM). Here we aim to enhance the AR-PAM image quality towards OR-PAM image, which specifically includes the enhancement of imaging resolution, restoration of micro-vasculatures, and reduction of artifacts. To address this issue, a network (MultiResU-Net) is first trained as generative model with simulated AR-OR image pairs, which are synthesized with physical transducer model. Moderate enhancement results can already be obtained when applying this model to in vivo AR imaging data. Nevertheless, the perceptual quality is unsatisfactory due to domain shift. Further, domain transfer learning technique under generative adversarial network (GAN) framework is proposed to drive the enhanced image’s manifold towards that of real OR image. In this way, perceptually convincing AR to OR enhancement result is obtained, which can also be supported by quantitative analysis. Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index (SSIM) values are significantly increased from 14.74 dB to 19.01 dB and from 0.1974 to 0.2937, respectively, validating the improvement of reconstruction correctness and overall perceptual quality. The proposed algorithm has also been validated across different imaging depths with experiments conducted in both shallow and deep tissue. The above AR to OR domain transfer learning with GAN (AODTL-GAN) framework has enabled the enhancement target with limited amount of matched in vivo AR-OR imaging data. [ABSTRACT FROM AUTHOR]

For precise health status monitoring and accurate disease diagnostics in the current COVID-19 pandemic, it is essential to detect various kinds of target signals robustly under high noise and strong interferences. Moreover, the health monitoring system is preferred to be realized in a small form factor for convenient mass deployments. A CMOS-integrated coherent sensing platform is proposed to achieve the goal, which synergetically leverages quadrature coherent photoacoustic (PA) detection and coherent radar sensing for achieving universal healthcare. By utilizing configurable mixed-signal quadrature coherent PA detection, high sensitivity and enhanced specificity can be achieved. In-phase (I) and quadrature (Q) templates are specifically designed to accurately sense and precisely reconstruct the target PA signals in a coherent mode. By mixed-signal implementation leveraging an FPGA to generate template waveforms adaptively, accurate tracking and precise reconstruction on the target PA signal can be attained based on the early-late tracking principle. The multiplication between the received PA signal and the templates is implemented efficiently in analog-domain by the Gilbert cell on-chip. In vivo blood temperature monitoring was realized based on the integrated PA sensing platform fabricated in a 65-nm CMOS process. With an integrated radar sensor deployed in the indoor scenario, noncontact monitoring on respiration and heartbeat rates can be attained based on electromagnetic (EM) sensing. By complementary usage of PA-EM sensing mechanisms, comprehensive health status monitoring and precise remote disease diagnostics can be achieved for the currentglobal COVID-19 pandemic and the future pervasive healthcare in the Internet of Everything (IoE) era. [ABSTRACT FROM AUTHOR]

Photoacoustic (PA) imaging is becoming more attractive because it can obtain high-resolution and high-contrast images through merging the merits of optical and acoustic imaging. High sensitivity receiver is required in deep in-vivo PA imaging due to detecting weak and noisy ultrasound signal. A novel photoacoustic receiver system-on-chip (SoC) with coherent detection (CD) based on the early-and-late acquisition and tracking is developed and first fabricated. In this system, a weak PA signal with negative signal-to-noise-ratio (SNR) can be clearly extracted when the tracking loop is locked to the input. Consequently, the output SNR of the receiver is significantly improved by about 29.9 dB than input one. For the system, a high dynamic range (DR) and high sensitivity analog front-end (AFE), a multiplier, a noise shaping (NS) successive-approximation (SAR) analog-to-digital convertor (ADC), a digital-to-analog convertor (DAC) and integrated digital circuits for the proposed system are implemented on-chip. Measurement results show that the receiver achieves 0.18 µVrms sensitivity at the depth of 1 cm with 1 mJ/cm2 laser output fluence. The contrast-to-noise (CNR) of the imaging is improved by about 22.2 dB. The area of the receiver is 5.71 mm2, and the power consumption of each channel is about 28.8 mW with 1.8 V and 1 V power supply on the TSMC 65 nm CMOS process. [ABSTRACT FROM AUTHOR]

Photoacoustic endoscopy (PAE), combining both advantages of optical contrast and acoustic resolution, can visualize the chemical-specific optical information of tissues inside human-body. Recently, its corresponding reconstruction methods have been extensively researched. However, most of them are limited on cylindrical scan trajectories, rather than a helical scan which is more clinically practical. On this note, this article proposes a methodology of imaging reconstruction and evaluation for helical scan guided PAE. Different from traditional reconstruction method, synthetic aperture focusing technique (SAFT), our method reconstructs image using wavefield extrapolation which significantly improves computational efficiency and even takes only 0.25 seconds for 3-D reconstructions. In addition, the proposed evaluation methodology can estimate the resolutions and deviations of reconstructed images in advance, and then can be used to optimize the PAE scan parameters. Groups of simulations as well as ex-vivo experiments with different scan parameters are provided to fully demonstrate the performance of the proposed techniques. The quantitatively measured angular resolutions and deviations agree well with our theoretical derivation results ${D}{\sqrt {r_{s}^{2} + \overline {h}^{{2}}} } / {[{1.25}({r}_{s} {r}_{d} + \overline {h}^{{2}})] }$ (rad) and $- \overline {h} {l} / ({r}_{s} {r}_{d} + \overline {h}^{{2}})$ (rad), respectively ${D},{r}_{d},\;{r}_{s},\overline {h} $ and ${l}$ represent transducer diameter, radius of scan trajectory, radius of source position, unit helical pitch and the distance from targets to helical scan plane, respectively). This theoretical result also suits for circular and cylindrical scan in case of $\overline {h} = {0}$. [ABSTRACT FROM AUTHOR]

A handheld approach to 3D photoacoustic imaging is essential in clinical applications. To this end, we develop a 3D handheld photoacoustic imager for dynamic (temporally and spatially) volumetric visualization. In this 3D imager, the optically transmitting part and the acoustically receiving part are integrated into a single handheld probe with a compact size about 160 mm $\times64$ mm $\times40$ mm. Besides, a dedicated imaging reconstruction algorithm for the heterogeneous medium is developed based on the phase-shift migration method in the frequency domain, which deals well with the stratified condition in the designed system. Dynamic 3D imaging supporting flexible handheld operation is demonstrated with needle biopsy and in vitro temperature measurement for photothermal therapy. The development of such a 3D handheld photoacoustic system paves the way for compact and handheld-operating implementations, and its further clinical exploration is promising. [ABSTRACT FROM AUTHOR]

Objective: A photoacoustic signal is proportional to the product of the optical absorption coefficient and the local light fluence; quantitative photoacoustic measurements of the optical absorption coefficients, therefore, require an accurate compensation of optical fluence variation. Usually, an additional diffuse optical tomography is incorporated to estimate the light fluence variation, but it is often troubled with the bulky measurement system. On this note, we present a dual-modality photoacoustic fusion imaging method that is implemented with a normal photoacoustic imaging (PAI) device. Methods: A single piezoelectric transducer is employed to receive the photoacoustic waves and passive ultrasound (PU) waves simultaneously. Since the PU wave is generated by the backscattering and diffuse reflection photons, it has the capacity to facilitate diffuse reflectance (DR) imaging. We merged photoacoustic and DR imaging based on their dual-modality with a compensation of the optical fluence variation. Results: The absorption coefficient differences caused by the light fluence variation are reduced more than half with the proposed method, when comparing to the pure photoacoustic imaging. Conclusion: The dual-modality photoacoustic fusion imaging is able to correct the PAI errors caused by the optical fluence variation. Significance: The proposed method can be widely accepted by different PAI applications to compensate the light fluence variations without any additional required element. [ABSTRACT FROM AUTHOR]

Diabetic patients need long-term and frequent glucose monitoring to assist in insulin intake. The current finger-prick devices are painful and costly, which places noninvasive glucose sensors in high demand. In this review paper, we list several advanced electromagnetic (EM)-wave-based technologies for noninvasive glucose measurement, including infrared (IR) spectroscopy, photoacoustic (PA) spectroscopy, Raman spectroscopy, fluorescence, optical coherence tomography (OCT), Terahertz (THz) spectroscopy, and microwave sensing. The development of each method is discussed regarding the fundamental principle, system setup, and experimental results. Despite the promising achievements that have been previously reported, no established product has obtained FDA approval or survived a marketing test. The limitations of, and prospects for, these techniques are presented at the end of this review. [ABSTRACT FROM AUTHOR]

This paper reviews the theories and applications of electromagnetic–acoustic (EMA) techniques (covering light-induced photoacoustic, microwave-induced thermoacoustic, magnetic-modulated thermoacoustic, and X-ray-induced thermoacoustic) belonging to the more general area of electromagnetic (EM) hybrid techniques. The theories cover excitation of high-power EM field (laser, microwave, magnetic field, and X-ray) and subsequent acoustic wave generation. The applications of EMA methods include structural imaging, blood flowmetry, thermometry, dosimetry for radiation therapy, hemoglobin oxygen saturation (SO2) sensing, fingerprint imaging and sensing, glucose sensing, pH sensing, etc. Several other EM-related acoustic methods, including magnetoacoustic, magnetomotive ultrasound, and magnetomotive photoacoustic are also described. It is believed that EMA has great potential in both pre-clinical research and medical practice. [ABSTRACT FROM AUTHOR]