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Shuo Qi,1– 3,* Gongyuan Liu,4 Jiangbo Chen,2,3 Peng Cao,1 Xiaohua Lei,1 Chengming Ding,1 Guodong Chen,1,* Yachao Zhang,2,3 Lidai Wang2,3 1Department of Hepatopancreatobiliary Surgery, The First Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, People’s Republic of China; 2Department of Biomedical Engineering, City University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China; 3Department of Biomedical Engineering, City University of Hong Kong Shenzhen Research Institute, Shenzhen, People’s Republic of China; 4Department of Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region, Peoples’s Republic of China*These authors contributed equally to this workCorrespondence: Yachao Zhang; Lidai Wang, Email yaczhang3-c@my.cityu.edu.hk; lidawang@cityu.edu.hkBackground: Effective theranostic of hepatocellular carcinoma (HCC) in an early-stage is imminently demanded to improve its poor prognosis. Combination of the near-infrared (NIR) photoacoustic imaging (PAI) and fluorescence imaging (FLI) can provide high temporospatial resolution, outstanding optical contrast, and deep penetration and thus is promising for accurate and sensitive HCC diagnosis.Methods: A versatile CXCR4-targeted Indocyanine green (ICG)/Platinum (Pt)-doped polydopamine melanin-mimic nanoparticle (designated ICG/Pt@PDA-CXCR4, referred to as IPP-c) is synthesized as an HCC-specific contrast agent for high-resolution precise diagnostic PAI/FLI and optical imaging-guided targeted photothermal therapy (PTT)/photodynamic therapy (PDT) of orthotopic small hepatocellular carcinoma (SHCC).Results: The multifunctional targeted nanoparticle yields superior HCC specificity, high imaging contrast in both PAI and FLI, good stability, reliable biocompatibility, effective singlet oxygen generation and superior photothermal conversion efficiency (PCE, 58.7%) upon 808-nm laser irradiation. The targeting ability of IPP-c was validated in in vitro experiments on selectively killing the CXCR4-overexpressing HCC cells. Moreover, we test the efficient dual-modal optical precision diagnosis properties of IPP-c via in vivo experiments on targeted particle accumulation in an early-stage SHCC mouse model (tumor diameter about 1.2 mm). Then, under the guidance of real-time optical imaging, effective and mini-invasive PTT/PDT of orthotopic SHCCs were demonstrated without damaging adjacent liver tissues or other major organs.Conclusion: This study presented a multifunctional CXCR4-targeted nanoparticle to conduct effective and mini-invasive phototherapeutics of orthotopic SHCCs via the real-time quantitative guidance by optical imaging, which provided a new perception for building a versatile targeted nanoplatform for phototheranostics of early-stage HCC.Keywords: hepatocellular carcinoma, CXCR4-targeted, photoacoustic imaging, photothermal therapy, photodynamic therapy

Developing probes to simultaneously detect and discriminate biothiols is important, yet challenging. Activatable photoacoustic (PA) probes for discriminating biothiols

Optical-resolution photoacoustic microscopy (OR-PAM) can image blood oxygen saturation (sO2) in vivo with high resolution and excellent sensitivity and offers a great tool for neurovascular study and early cancer diagnosis. OR-PAM ignores the wavelength-dependent optical attenuation in superficial tissue, which cause errors in sO2 imaging. Monte Carlo simulation shows that variations in imaging depth, vessel diameter, and focal position can cause up to ~60% decrease in sO2 imaging. Here, we develop a self-fluence-compensated OR-PAM to compensate for the wavelength-dependent fluence attenuation. We propose a linearized model to estimate the fluence attenuations and use three optical wavelengths to compensate for them in sO2 calculation. We validate the model in both numerical and physical phantoms and show that the compensation method can effectively reduce the sO2 errors. In functional brain imaging, we demonstrate that the compensation method can effectively improve sO2 accuracy, especially in small vessels. Compared with uncompensated ones, the sO2 values are improved by 10~30% in the brain. We monitor ischemic-stroke-induced brain injury which demonstrates great potential for the preclinical study of vascular diseases.

Photoacoustic endoscopy shows promise in the detection of gastrointestinal cancer, inflammation, and other lesions. High-resolution endoscopic imaging of the hemodynamic response necessitates a small-sized, high-sensitivity ultrasound sensor. Here, we utilize a laser ultrasound sensor to develop a miniaturized, optical-resolution photoacoustic endoscope. The sensor can boost the acoustic response by a gain factor of ωo/Ω (the frequency ratio of the signal light and measured ultrasound) by measuring the acoustically induced optical phase change. As a result, we achieve a noise-equivalent pressure density (NEPD) below 1.5 mPa·Hz−1/2 over the measured range of 5 to 25 MHz. The heterodyne phase detection using dual-frequency laser beams of the sensor can offer resistance to thermal drift and vibrational perturbations. The endoscope is used to in vivo image a rat rectum and visualize the oxygen saturation changes during acute inflammation, which can hardly be observed with other imaging modalities.

Optical-resolution photoacoustic microscopy offers high-resolution, label-free hemodynamic and functional imaging to many biomedical applications. However, long-standing technical barriers, such as limited field of view, bulky scanning probes, and slow imaging speed, have limited the application of optical-resolution photoacoustic microscopy. Here, we present freehand scanning photoacoustic microscopy (FS-PAM) that can flexibly image various anatomical sites. We develop a compact handheld photoacoustic probe to acquire 3D images with high speed, and great flexibility. The high scanning speed not only enables video camera mode imaging but also allows for the first implementation of simultaneous localization and mapping (SLAM) in photoacoustic microscopy. We demonstrate fast in vivo imaging of some mouse organs, and human oral mucosa. The high imaging speed greatly reduces motion artifacts and distortions from tissue moving, breathing, and unintended handshaking. We demonstrate small-lesion localization in a large region of the brain. FS-PAM offers a flexible high-speed imaging tool with an extendable field of view, enabling more biomedical imaging applications.

A combined treatment using medication and electrostimulation increases its effectiveness in comparison with one treatment alone. However, the organic integration of two strategies in one miniaturized system for practical usage has seldom been reported. This article reports an implantable electronic medicine based on bioresorbable microneedle devices that is activated wirelessly for electrostimulation and sustainable delivery of anti-inflammatory drugs. The electronic medicine is composed of a radio frequency wireless power transmission system and a drug-loaded microneedle structure, all fabricated with bioresorbable materials. In a rat skeletal muscle injury model, periodic electrostimulation regulates cell behaviors and tissue regeneration while the anti-inflammatory drugs prevent inflammation, which ultimately enhance the skeletal muscle regeneration. Finally, the electronic medicine is fully bioresorbable, excluding the second surgery for device removal.

Acoustic-resolution photoacoustic micro- scopy (AR-PAM) system can provide 3-D images of facial tissues. The lateral resolution of AR-PAM depends on the numerical aperture (NA) of the acoustic lens and the central frequency of the ultrasonic transducer. There is a trade-off between resolution enhancement and imaging depth. The acoustic beam is tight in the acoustic focal plane but expands in the out-of-focus regions, deteriorating the resolution. High-NA AR-PAM has depth-variant resolution. Synthetic aperture focusing technique (SAFT) based on a virtual detector (VD) concept can compensate for the beam shape and improve the lateral resolution via beamforming. Although, beamforming can enhance the resolution but the lateral resolution in the focal plane is still limited by acoustic diffraction. Structured-illumination can shift the spatial spectrum of an image to low frequencies hence high-frequency contents can be reserved to overcome the diffraction limit. Conventional structured-illumination via using a three-phase-shifting method can improve the resolution by two folds. Here, a modified phase-shifting method is used to generate the second harmonic of the fringes and double the spectral shift. In this idea, higher frequency information compared to the three-phase shifting method can fall into the band-limited system response. The modified phase-shifting method expands the spatial bandwidth and increases the lateral resolution by five folds. The mathematical relations and the theory are discussed in the context. Tungsten filament result shows resolution improvement from 44.6 [Formula: see text] to 11.3 [Formula: see text] by the modified structured illumination. In vivo and ex vivo experimental results validate the system performance.

Full-ring dual-modal ultrasound and photoacoustic computed tomography has unique advantages of nearly isotropic spatial resolution, complementary contrast, deep penetration, and full-view detection. However, the imaging quality may be deteriorated by the inaccurate sound speed estimation. Automatic determining and compensation for sound speed has been a long-standing problem in image reconstruction. Here, we present new adaptive dual-speed ultrasound and photoacoustic computed tomography (ADS-USPACT) to address this challenge. The system features full-view coverage (360°), high-speed dual-modal imaging (10-Hz), automated dual sound speed correction, and synergistic high imaging quality. To correct the sound speed, we develop a two-compartment method that can automatically segment the sample boundary and search for the optimal sound speed based on the rich ultrasonic pulse-echo signals. The method does not require the operator's intervention. We validate this technique in numerical simulation, phantom study, and in vivo experiments. The ADS-USPACT represents significant progress in dual-modal imaging.

Simultaneous photoacoustic (PA) and ultrasound (US) imaging provides rich optical and acoustic contrasts with high sensitivity, specificity, and resolution, making it a promising tool for diagnosing and assessing various diseases. However, the resolution and penetration depth tend to be contradictory due to the increased attenuation of high-frequency ultrasound. To address this issue, we present simultaneous dual-modal PA/US microscopy with an optimized acoustic combiner that can maintain high resolution while improving the penetration of ultrasound imaging. A low-frequency ultrasound transducer is used for acoustic transmission, and a high-frequency transducer is used for PA and US detection. An acoustic beam combiner is utilized to merge the transmitting and receiving acoustic beams with a predetermined ratio. By combining the two different transducers, harmonic US imaging and high-frequency photoacoustic microscopy are implemented. In vivo experiments on the mouse brain demonstrate the simultaneous PA and US imaging ability. The harmonic US imaging of the mouse eye reveals finer iris and lens boundary structures than conventional US imaging, providing a high-resolution anatomical reference for co-registered PA imaging.

Ultrasonography and photoacoustic tomography provide complementary contrasts in preclinical studies, disease diagnoses, and imaging-guided interventional procedures. Here, we present a video-rate (20 Hz) dual-modality ultrasound and photoacoustic tomographic platform that has a high resolution, rich contrasts, deep penetration, and wide field of view. A three-quarter ring-array ultrasonic transducer is used for both ultrasound and photoacoustic imaging. Plane-wave transmission/receiving approach is used for ultrasound imaging, which improves the imaging speed by nearly two folds and reduces the RF data size compared with the sequential single-channel scanning approach. GPU-based image reconstruction is developed to advance computational speed. We demonstrate fast dual-modality imaging in phantom, mouse, and human finger joint experiments. The results show respiration motion, heart beating, and detailed features in the mouse internal organs. To our knowledge, this is the first report on fast plane-wave ultrasound imaging and single-shot photoacoustic computed tomography in a ring-array system.

Photoacoustic microscopy can image various biological molecules and nano-agents in vivo via low-scattering ultrasonic sensing. Insufficient sensitivity has been a long-standing obstacle for imaging of many low-absorbing chromophores with less photobleaching or toxicity, reduced perturbation to delicate organs, and more choices of lasers. Here, we present a multi-spectral super-low-dose photoacoustic microscopy (SLD-PAM) that is up to ~ 33-times more sensitive than the state of the art. We collaboratively innovate the photoacoustic probe design and implement a spectral-spatial filter. The new probe collects 300% more acoustic signals, and the filter further improves the signal-to-noise ratio by 200%~1100% across all optical wavelengths. SLD-PAM can visualize microvessels and quantify oxygen saturation (sO2) in vivo with ~ 1% of the maximum permissible exposure, dramatically reducing any possible phototoxicity or perturbation, especially in imaging of the eye and the brain. Capitalizing on the high sensitivity, we, for the first time, implement direct imaging of deoxyhemoglobin (Deoxy-Hb) concentration without spectral unmixing, avoiding wavelength-dependent and computational noises. We show that super-low-dose molecular imaging can reduce photobleaching by at least 85%. We also demonstrate SLD-PAM achieves similar molecular imaging quality using 80% fewer contrast agents, which greatly reduces potential biotoxicity. SLD-PAM enables the use of more low-absorbing nano-agents, small molecules, and genetically-encoded biomarkers, as well as more low-power light sources at wider spectra. We believe SLD-PAM offers a powerful tool for anatomical, functional, and molecular imaging.

Convex probes have been widely used in clinical abdominal imaging for providing deep penetration and wide field of view. Ultrafast imaging modalities have been studied extensively in the ultrasound community. Specifically, broader wavefronts, such as plane wave and spherical wave, are used for transmission. For convex array, spherical wavefront can be simply synthesized by turning all elements simultaneously. Due to the lack to transmit focus, the image quality is suboptimal. One solution is to adopt virtual sources behind the transducer and compound corresponding images. In this work, we propose two novel Fourier-domain beamformers (vs1 and vs2) for nonsteered diverging wave imaging and an explicit interpolation scheme for virtual-source-based steered diverging wave imaging using a convex probe. The received echoes are first beamformed using the proposed beamformers and then interpolated along the range axis. A total of 31 virtual sources located on a circular line are used. The lateral resolution, the contrast ( C ), and the contrast-to-noise ratio (CNR) are evaluated in simulations, phantom experiments, ex vivo imaging of the bovine heart, and in vivo imaging of the liver. The results show that the two proposed Fourier-domain beamformers give higher contrast than dynamic receive focusing (DRF) with better resolution. In vitro results demonstrate the enhancement on CNR: 6.7-dB improvement by vs1 and 5.9-dB improvement by vs2. Ex vivo imaging experiments on the bovine heart validate the CNR enhancements by 8.4 dB (vs1) and 8.3 dB (vs2). In vivo imaging on the human liver also reveals 6.7- and 5.5-dB improvements of CNR by vs1 and vs2, respectively. The computation time of vs1 and vs2, depending on the image pixel number, is shortened by 2-73 and 4-216 times than the DRF.

Complexities of the underwater environment can seriously affect many underwater detection means, especially the influence of light scattering by water. To solve this problem, a three-dimensional (3D) morphology measurement method is proposed based on the photoacoustic effect. In this method, a measurement object is irradiated with pulsed laser light to produce ultrasonic waves via the photoacoustic effect. A probe collects the ultrasonic signal and subsequent data processing can yield complete object detection. This approach can make full use of the advantages of high precision and good directivity of laser ranging and completely avoid the influence on the laser of backscattering from water. The results yield a displacement measurement accuracy of less than 0.5 mm and an average error of 3D reconstruction of 0.21 mm, demonstrating great application potential.

The potassium ion (K+) plays significant roles in many biological processes. To date, great efforts have been devoted to the development of K+ sensors for colorimetric, fluorescent, and photoacoustic detection of K+ separately. However, the development of molecular K+ probes for colorimetric detection of urinary K+, monitoring K+ fluxes in living cells by fluorescence imaging, and photoacoustic imaging of K+ dynamics in deep tissues still remains an open challenge. Herein, we report the first molecular K+ probe (NK2) for colorimetric, fluorescent, and photoacoustic detection of K+. NK2 is composed of 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as the chromophore and phenylazacrown-6-lariat ether (ACLE) as the K+ recognition unit. Predominate features of NK2 include a short synthetic procedure, high K+ selectivity, large detection range (5–200 mM), and triple-channel detection manner. NK2 shows good response to K+ with obvious color changes, fluorescence enhancements (about threefold), and photoacoustic intensity changes. The existence of other metal ions (including Na+, Mg2+, Ca2+, Fe2+) and pH changes (6.5–9.0) have no obvious influence on K+ sensing of NK2. Portable test strips stained by NK2 can be used to qualitatively detect urinary K+ by color changes for self-diagnosis of diseases induced by high levels of K+. NK2 can be utilized to monitor K+ fluxes in living cells by fluorescent imaging. We also find its excellent performance in photoacoustic imaging of different K+ concentrations in the mouse ear. NK2 is the first molecular K+ probe for colorimetric, fluorescent, and photoacoustic detection of K+ in urine, in living cells, and in the mouse ear. The development of NK2 will broaden K+ probes’ design and extend their applications to different fields.

Hydrogen sulfide (H2S) has been recognized to influence a wide range of physiological and pathological processes. Its underlying molecular events, however, are still poorly understood. An activatab...

Current embodiments of photoacoustic imaging require either serial detection with a single-element ultrasonic transducer or parallel detection with an ultrasonic array, necessitating a trade-off between cost and throughput. Here, we present photoacoustic topography through an ergodic relay (PATER) for low-cost high-throughput snapshot wide-field imaging. Encoding spatial information with randomized temporal signatures through ergodicity, PATER requires only a single-element ultrasonic transducer to capture a wide-field image with a single laser shot. We applied PATER to demonstrate both functional imaging of haemodynamic responses and high-speed imaging of blood pulse wave propagation in mice in vivo. Leveraging the high frame rate of 2 kHz, PATER tracked and localized moving melanoma tumour cells in the mouse brain in vivo, which enabled flow velocity quantification and super-resolution imaging. Among the potential biomedical applications of PATER, wearable devices to monitor human vital signs in particular is envisaged.

Hydrogen sulfide (H

In a photoacoustic (PA) imaging system, the detectors are bandwidth-limited. Therefore, they capture PA signals with some unwanted ripples. This limitation degrades the resolution/contrast and induces sidelobes and artifacts in the reconstructed images along the axial direction. To compensate for the limited bandwidth effect, we present a PA signal restoration algorithm, where a mask is designed to extract the signals at the absorber positions and remove the unwanted ripples. This restoration improves the axial resolution and contrast in the reconstructed image. The restored PA signals can be considered as the input of the conventional reconstruction algorithms (e.g., Delay-and-sum (DAS) and Delay-multiply-and-sum (DMAS)). To compare the performance of the proposed method, DAS and DMAS reconstruction algorithms were performed with both the initial and restored PA signals on numerical and experimental studies (numerical targets, tungsten wires, and human forearm). The results show that, compared with the initial PA signals, the restored PA signals can improve the axial resolution and contrast by 45% and 16.1 dB, respectively, and suppress background artifacts by 80%.

Optical-resolution photoacoustic microscopy (OR-PAM) is used for in vivo imaging of a variety of albino and pigmented eyes taking advantages of requiring no exogenous dye, performing high-resolution imaging, and achieving morphologic and functional imaging at the same time. However, to accurately diagnose the ophthalmic disease in the OR-PAM images, vascular enhancement algorithms are necessary for extracting vessels and quantifying them correctly. Vascular enhancement algorithms developed for other imaging technologies, are not suitable to be used for OR-PAM, because of the underlying differences in the physics of the formation of images. In this study, a new vascular enhancement algorithm called photoacoustic imaging vasculature enhancement filter (PAIVEF) is proposed, which not only enhances vasculature including micro-vessels signals, suppresses noise signals effectively, but also achieves highly sensitive and accurate enhancement of the vasculature within a large depth range in and out of the system's depth of focus (DOF). Using the PAIVEF, the morphologic and functional 3D images of the whole rat's ocular anterior vasculature segment was displayed simultaneously for a depth range of ~0.6 mm, which was ~7 times of the system's DOF. This study paves the way for the application of OR-PAM technology in ophthalmic disease research.

Early diagnosis and effective treatment of hepatocellular carcinoma (HCC) is quite critical for improving patients’ prognosis. The combination of second near-infrared window photoacoustic imaging (NIR-II PAI) and T2-magnetic resonance imaging (T2-MRI) is promising for achieving omnibearing information on HCC diagnosis due to the complementary advantages of outstanding optical contrast, high temporospatial resolution and soft-tissue resolution. Thus, the rational design of a multifunctional targeted nanoplatform with outstanding performance in dual-modal NIR-II PAI/T2-MRI is particularly valuable for precise diagnosis and imaging-guided non-invasive photothermal therapy (PTT) of early-stage HCC. Herein, a versatile targeted organic–inorganic hybrid nanoprobe was synthesized as a HCC-specific contrast agent for sensitive and efficient theranostics. The developed multifunctional targeted nanoprobe yielded superior HCC specificity, reliable stability and biocompatibility, high imaging contrast in both NIR-II PAI and T2-MRI, and an excellent photothermal conversion efficiency (74.6%). Furthermore, the theranostic efficiency of the targeted nanoprobe was systematically investigated using the orthotopic early HCC-bearing mice model. The NIR-II PAI exhibited sensitive detection of ultra-small HCCs (diameter less than 1.8 mm) and long-term real-time monitoring of the tumor and nanoprobe targeting process in deep tissues. The T2-MRI demonstrated clear imaging contrast and a spatial relationship between micro-HCC and adjacent structures for a comprehensive description of the tumor. Moreover, when using the targeted nanoprobe, the non-invasively targeted PTT of orthotopic early HCC was carried out under reliable dual-modal imaging guidance with remarkable anti-tumor efficiency and biosafety. This study provides an insight for constructing a multifunctional targeted nanoplatform for precise and comprehensive theranostics of early-stage HCC, which would greatly benefit the patients in the era of precision medicine.

Optical-resolution photoacoustic microscopy (OR-PAM) enjoys superior spatial resolution and has received intense attention in recent years. The application, however, has been limited to shallow depths because of strong scattering of light in biological tissues. In this work, we propose to achieve deep-penetrating OR-PAM performance by using deep learning enabled image transformation on blurry living mouse vascular images that were acquired with an acoustic-resolution photoacoustic microscopy (AR-PAM) setup. A generative adversarial network (GAN) was trained in this study and improved the imaging lateral resolution of AR-PAM from 54.0 µm to 5.1 µm, comparable to that of a typical OR-PAM (4.7 µm). The feasibility of the network was evaluated with living mouse ear data, producing superior microvasculature images that outperforms blind deconvolution. The generalization of the network was validated with in vivo mouse brain data. Moreover, it was shown experimentally that the deep-learning method can retain high resolution at tissue depths beyond one optical transport mean free path. Whilst it can be further improved, the proposed method provides new horizons to expand the scope of OR-PAM towards deep-tissue imaging and wide applications in biomedicine.

Photoacoustic microscopy uses multiple wavelengths to measure concentrations of different absorbers. The speed of sound limits the shortest wavelength switching time to sub-microseconds, which is a bottleneck for high-speed broad-spectrum imaging. Via computational separation of overlapped signals, we can break the sound-speed limit on the wavelength switching time. This paper presents a new signal unmixing algorithm named two-step proximal gradient descent. It is advantageous in separating multiple wavelengths with long overlapping and high noise. In the simulation, we can unmix up to nine overlapped signals and successfully separate three overlapped signals with 12-ns delay and 15.9-dB signal-to-noise ratio. We apply this technique to separate three-wavelength photoacoustic images in microvessels. In vivo results show that the algorithm can successfully unmix overlapped multi-wavelength photoacoustic signals, and the unmixed data can improve accuracy in oxygen saturation imaging.

We present the development of a new low-cost and portable nanophotonic sensor to measure mechanical or environmental quantities, such as acoustic, bending, stretching, or temperature changes (see Figure 1). The sensor consists of a compact diode laser, a multimode fiber, and a smartphone, and thus, it is quite portable. The laser light emitted from the multimode fiber forms optical speckle patterns on a screen. We experimentally implement the bending sensing on a smartphone. The relationship between the bending curvature and the optical speckle pattern is quantitatively studied, demonstrating its feasibility of bending sensing.

Full-ring dual-modal ultrasound and photoacoustic imaging provide complementary contrasts, high spatial resolution, full view angle and are more desirable in pre-clinical and clinical applications. However, two long-standing challenges exist in achieving high-quality video-rate dual-modal imaging. One is the increased data processing burden from the dense acquisition. Another one is the object-dependent speed of sound variation, which may cause blurry, splitting artifacts, and low imaging contrast. Here, we develop a video-rate full-ring ultrasound and photoacoustic computed tomography (VF-USPACT) with real-time optimization of the speed of sound. We improve the imaging speed by selective and parallel image reconstruction. We determine the optimal sound speed via co-registered ultrasound imaging. Equipped with a 256-channel ultrasound array, the dual-modal system can optimize the sound speed and reconstruct dual-modal images at 10 Hz in real-time. The optimized sound speed can effectively enhance the imaging quality under various sample sizes, types, or physiological states. In animal and human imaging, the system shows co-registered dual contrasts, high spatial resolution (140 µm), single-pulse photoacoustic imaging (< 50 µs), deep penetration (> 20 mm), full view, and adaptive sound speed correction. We believe VF-USPACT can advance many real-time biomedical imaging applications, such as vascular disease diagnosing, cancer screening, or neuroimaging.

Accurate identification and quantification of microvascular patterns are important for clinical diagnosis and therapeutic monitoring using optical-resolution photoacoustic microscopy (OR-PAM). Due to its limited depth of field, conventional OR-PAM may not fully reveal microvascular patterns with enough details in depth range, which affects the segmentation and quantification. Here, we propose a robust vascular quantification approach via combining multi-focus image fusion with enhancement filtering (MIFEF). The multi-focus image fusion is constructed based on multi-scale gradients and image matting to improve image fusion quality by considerably achieving accurate focus measurement for initial segmentation as well as decision map refinement. The enhancement filtering identifies the vessels and handles noise without deforming microvasculature. The performance of the MIFEF were evaluated employing a leaf phantom, mouse livers and brains. The proposed method for OR-PAM can significantly facilitate the clinical provision of optical biopsy of vascular-related diseases.

Glutathione is overexpressed in tumor cells and regulates cancer growth, metastasis, and drug resistance. Therefore, detecting glutathione levels may greatly facilitate cancer diagnosis and treatment response monitoring. Photoacoustic (PA) imaging is a noninvasive modality for high-sensitivity, high-resolution, deep-tissue optical imaging. Switchable PA probes that offer signal on/off responses to tumor targets would further improve the detection sensitivity and signal-to-noise ratio of PA imaging. Here, we explore the use of MnO2 nanotubes as a switchable and biodegradable PA probe for dynamic imaging of glutathione in cancer. Glutathione reduces black MnO2 nanotubes into colorless Mn2+ ions, leading to decreased and signal off PA amplitude. In phantoms, we observed a linear response of reduced PA signals of MnO2 nanotubes to increased glutathione concentrations. Using melanoma as the disease model, we demonstrated that MnO2 nanotube-based PA imaging of glutathione successfully distinguished B16F10 melan...

Here we report a high performance fiber-based photoacoustic microscope for brain sO2 imaging. The critical element is a fiber-optic ultrasound sensor, which translates the megahertz acoustic waves into detectable lasing frequency variations. Its working bandwidth has been extended to 40 MHz, by reducing the fiber diameter to 58 μm via chemical etching, this sensor should good result in brain sO2 imaging. The fiber-based PAM offers a new strategy to implement a head-mounted microscope to continuously monitor the brain activities of an awake, free-moving small animal.

Optical-resolution photoacoustic microscopy (OR-PAM) can image the blood oxygen saturation (sO2) in vivo without labeling. OR-PAM assumes a linear relationship between the photoacoustic amplitude and the optical absorption coefficient and ignores the wavelength-dependent optical fluence attenuation in tissue. However, strong scattering in biological tissues may significantly change the optical energy deposition, leading to inaccurate sO2 measurement. Here, we report fluence-compensated OR-PAM to correct the sO2 imaging. In a narrow optical spectrum, we assume the scattered fluence is linearly related to the optical wavelength. Using three optical wavelengths, we can compensate for the scattering-induced photoacoustic signal change and thus improve the accuracy of sO2 measurement. We use a Monta Carlo model to validate the linear assumption of the scattered fluence. In in vivo experiments, we demonstrate that the optical fluence compensation can effectively improve the sO2 accuracy. The compensated arterial sO2 values are in the range of 0.95 ~ 0.99, which is consistent with normal physiological values. Compared with the uncompensated ones, the accuracy has been improved greatly. Enabled by the accurate sO2 imaging tool, we can reliably observe the sO2 gradient in the vascular network. We expect this new technique will further broaden the preclinical and clinical applications of functional OR-PAM.

Optical-resolution photoacoustic microscopy (OR-PAM) has been developed for anatomical, functional, and molecular imaging but usually requires multiple scanning for different contrasts. We present five-wavelength OR-PAM for simultaneous imaging of hemoglobin concentration, oxygen saturation, blood flow speed, and lymphatic vessels in single raster scanning. We develop a five-wavelength pulsed laser via stimulated Raman scattering. The five pulsed wavelengths, i.e., 532, 545, 558, 570, and 620 / 640 nm, are temporally separated by several hundreds of nanoseconds via different optical delays in fiber. Five photoacoustic images at these wavelengths are simultaneously acquired in a single scanning. The 532- and 620 / 640-nm wavelengths are used to image the blood vessels and dye-labeled lymphatic vessels. The blood flow speed is measured by a dual-pulse method. The oxygen saturation is calculated and compensated for by the Gruneisen-relaxation effect. In vivo imaging of hemoglobin concentration, oxygen saturation, blood flow speed, and lymphatic vessels is demonstrated in preclinical applications of cancer detection, lymphatic clearance monitoring, and functional brain imaging.

We report fiber-based confocal visible/near-infrared optical-resolution photoacoustic microscopy that can image tumor microvasculature, oxygen saturation, and nanoprobes in a single scanning. It offers a new tool for early detection of tumors with multiple contrast modes.

Oxygen saturation (sO2) imaging can offer useful information for pathological studies and clinical diagnostics. Here we report on a fiber-based photoacoustic microscope for functional brain imaging. The critical element is a fiber-optic ultrasound sensor, which translates the megahertz acoustic waves into detectable lasing frequency variations. Its working bandwidth has been extended to 40 MHz, by reducing the fiber diameter to 58 μm via chemical etching. As a result, in vivo sO2 imaging of a mouse brain can be performed by using a dual-wavelength excitation scheme, taking advantage of the difference in the absorption spectrum between the oxygenated (HbO2) and deoxygenated hemoglobin (HbR). The broadband ultrasound detection can effectively overcome the saturation effect originated from the strong optical absorption. The fiber optic photoacoustic probe paves the way for the implementation of a light-weight, wearable brain imager for awake, freely-moving animals.

As a traditional Chinese medicine practice, cupping therapy has been widely used for thousands of years to promote blood circulation and release symptoms of some diseases. The actual effect, however, has been debatable due to the lack of scientific evidence. Aiming to objectively assess the treatment effect, in this study we introduce optical-resolution photoacoutic microscopy to monitor the structural and functional changes of microenvironment parameters pre- and post-cupping through facial cups. Whilst further investigation is in demand, this pilot study provides a new imaging perspective to understand the mechanism and evaluate the effect of cupping therapy.

Label-free chemical bond imaging is of great importance in biology and medicine. Photoacoustic imaging at the third near-infrared windows (1600-1870 nm, nearinfrared-III) provides a stable molecular vibrational imaging tool for lipid-rich tissue owing to the first overtone transition of the C-H bond at 1.7 _m. However, lacking high-energy pulsed laser sources at 1.7 _m and the strong water absorption significantly limit the signal-to-noise ratio of the lipid imaging, especially for thin lipid tissues. To circumvent this barrier, we develop near-infrared-III double-illumination optical-resolution photoacoustic microscopy (DIOR-PAM) for improving the sensitivity of label-free lipid imaging. Using the same laser, DIOR-PAM can enhance the sensitivity by nearly 100%, which we prove in the Monte Carlo simulation.We experimentally demonstrated 50%i100% sensitivity enhancement on non-biological and biological lipid-rich samples. This article is protected by copyright. All rights reserved.

Photoacoustic agents have been of vital importance for improving the imaging contrast and reliability against self-interference from endogenous substances. Herein, we synthesized a series of thiadiazoloquinoxaline (TQ)-based semiconducting polymers (SPs) with a broad absorption covering from NIR-I to NIR-II regions. Among them, the excited s-BDT-TQE, a repeating unit of SPs, shows a large dihedral angle and narrow adiabatic energy as well as low radiative decay, attributing to its strongly electron-deficient ester-substituted TQ-segment. In addition, its more vigorous molecular motions trigger a higher reorganization energy that further yields an efficient photoinduced nonradiative decay, which has been carefully examined and understood by theoretical calculation. Thus, BDT-TQE SP-cored nanoparticles with twisted intramolecular charge transfer (TICT) feature exhibit a high NIR-II photothermal conversion efficiency (61.6 %) and preferable PA tracking of in situ hepatic tumor growth for more than 20 days. This study highlights a unique strategy for constructing efficient NIR-II photoacoustic agents via TICT-enhanced PNRD effect, advancing their applications for in vivo bioimaging.

Precise diagnosis and effective treatment of gliomas still remain a huge challenge. Photoacoustic-guided photothermal therapy (PTT) has unique advantages over conventional techniques for brain tumor theranostics, but existing nanoagents for photoacoustic imaging (PAI)-guided PTT are mainly organic small molecules or inorganic nanoparticles, which have the limitations of poor photostability and biocompatibility. Besides, the restricted absorption in the first near-infrared window (NIR-I) of the most existing nanoagents compromises their effectiveness for deep tissue PAI and PTT. We herein develop novel semiconducting polymer nanoparticles (SPNs) that are strongly absorptive in the second NIR window (NIR-II) to alleviate these problems. With the merits of excellent photoacoustic and photothermal performance, high photostability, proper size, and low toxicity, SPNs not only show efficient cellular uptake for PAI and PTT toward U87 glioma cells but also demonstrate effective accumulation in both subcutaneous tumors and brain tumors upon intravenous injection, thereby realizing efficient PAI-guided PTT toward gliomas under NIR-II light irradiation.

The potassium ion (K

This Conference Presentation, “Compressed Ultrafast Spectral Temporal (CUST) photography” was recorded at Photonics West LASE 2020, held in San Francisco, California, United States of America.

Due to limited ultrasound detection angle, photoacoustic microscopy may own a relatively low sensitivity. To break this limit, we develop an ultra-sensitive optical resolution photoacoustic microscopy based on a customized acoustic lens with high numerical aperture (0.74) (HNA-OR-PAM). The sensitivity of HNA-OR-PAM is improved to around 160% as the state-of-the-art OR-PAM. It has the capability to measure oxygen saturation of mice’s ear in vivo with ~10nJ pulse energy, reducing the nonlinear effect induced by high pulse energy. In addition, photoacoustic signal of tilted objects could be enhanced due to augmented ultrasound detection angle, which has been validated in our phantom study and the brain imaging experiment in vivo.

Fast switch between pulses of sufficient energy but different wavelengths plays an important role in fast functional photoacoustic imaging. Commonly used Stimulated Raman scattering through a long optical fiber can produce multiple wavelengths, but longer fiber means lower energy, which would decrease image quality. Shorter optical fiber is thus more desired for fast imaging. However, it should be noted that too short pulse separation may generate photoacoustic signals that are temporally overlapped. Here, we propose an approach to solve this overlapping problem in ultrafast PA imaging using a Fourier-domain based method. The validity of this method is confirmed through simulation firstly, and then it is applied to separate overlapped PA signals. Lastly, in vivo OR-PAM mapping of mouse ear’s sO2 photoacoustic imaging is achieved.

Fast functional and molecular photoacoustic microscopy requires pulsed laser excitations at multiple wavelengths with enough pulse energy and short wavelength-switching time. Recent development of stimulated Raman scattering in optical fiber offers a low-cost laser source for multiwavelength photoacoustic imaging. In this approach, long fibers temporally separate different wavelengths via optical delay. The time delay between adjacent wavelengths may eventually limits the highest A-line rate. In addition, a long-time delay in fiber may limit the highest pulse energy, leading to poor image quality. In order to achieve high pulse energy and ultrafast dual-wavelength excitation, we present optical-resolution photoacoustic microscopy with ultrafast dual-wavelength excitation and a signal separation method. The signal separation method is validated in numerical simulation and phantom experiments. We show that when two photoacoustic signals are partially overlapped with a 50-ns delay, they can be recovered with 98% accuracy. We apply this ultrafast dual-wavelength excitation technique to in vivo OR-PAM. Results demonstrate that A-lines at two wavelengths can be successfully separated, and sO2 values can be reliably computed from the separated data. The ultrafast dual-wavelength excitation enables fast functional photoacoustic microscopy with negligible misalignment among different wavelengths and high pulse energy, which is important for in vivo imaging of microvascular dynamics.

It remains highly challenging to identify small molecule-based photothermal agents with a high photothermal conversion efficiency (PTCE). Herein, we adopt a double bond-based molecular motor concept to develop a new class of small photothermal agents to break the current design bottleneck. As the double-bond is twisted by strong twisted intramolecular charge transfer (TICT) upon irradiation, the excited agents can deactivate non-radiatively through the conical intersection (CI) of internal conversion, which is called photoinduced nonadiabatic decay. Such agents possess a high PTCE of 90.0 %, facilitating low-temperature photothermal therapy in the presence of a heat shock protein 70 inhibitor. In addition, the behavior and mechanism of NIR laser-triggered molecular motions for generating heat through the CI pathway have been further understood through theoretical and experimental evidence, providing a design principle for highly efficient photothermal and photoacoustic agents.

Optical detection of ultrasound for photoacoustic imaging has received great interest. Recently, we have developed a new fiber-optic ultrasound sensor by exploiting dual-polarization fiber laser. It offers high sensitivity (40 Pa over 50 MHz) as well as good stability as a result of the self-heterodyning detection. In this work, the signal-to-noise ratio has been enhanced by suppressing the noise of the ultrasound sensing system via signal averaging. As a result of multiple measurements of a single photoacoustic signal, the total noise was reduced by 40%. With the enhanced detection capability, the sensors have been deployed as photoacoustic probes in different imaging modalities. We demonstrate fastscanning photoacoustic microscopy with a field-of-view 2×2 mm2, a frame rate of 2 Hz to visualize the blood flow dynamics. By bending the flexible fiber optic sensor for geometrical focusing, PACT was realized to image a mouse brain with a spatial resolution of 70 μm. An all-fiber photoacoustic endoscope was built to in vivo image the vascular network of a rat rectum, with a lateral resolution of 10 μm, with a 2.3-mm probe diameter.

Limited by the numerical aperture of ultrasonic detection, optical resolution photoacoustic microscopy (OR-PAM) has not achieved optimal sensitivity. To address this problem, we have developed a high acoustic numerical aperture ( ∼ 0.74 ) OR-PAM (HNA-OR-PAM). Via engineering the acoustic lens, we implement the highest acoustic numerical aperture that a spherical concave lens can achieve. The sensitivity of HNA-OR-PAM is improved to around 160%—the state-of-the-art OR-PAM. Without averaging, the new system can image oxygen saturation in vivo with only 10-nJ pulse energy. The improved sensitivity allows us to image weaker absorbers, penetrate deeper, and reduce nonlinear effects induced by high pulse energy. Moreover, the photoacoustic view angle is augmented to 51.8 deg and makes tilted features more visible. We validate the improved view angle in both a phantom study and brain imaging.

Functional intestinal imaging holds importance for the diagnosis and evaluation of treatment of gastrointestinal diseases. Currently, preclinical imaging of intestinal motility in animal models is performed either invasively with excised intestines or noninvasively under anesthesia, and cannot reveal intestinal dynamics in the awake condition. Capitalizing on near-infrared optics and a high-absorbing contrast agent, we report the Trans-illumination Intestine Projection (TIP) imaging system for free-moving mice. After a complete system evaluation, we performed in vivo studies, and obtained peristalsis and segmentation motor patterns of free-moving mice. We show the in vivo typical segmentation motor pattern, that was previously shown in ex vivo studies to be controlled by intestinal pacemaker cells. We also show the effects of anesthesia on motor patterns, highlighting the possibility to study the role of the extrinsic nervous system in controlling motor patterns, which requires unanesthetized live animals. Combining with light-field technologies, we further demonstrated 3D imaging of intestine in vivo (3D-TIP). Importantly, the added depth information allows us to extract intestines located away from the abdominal wall, and to quantify intestinal motor patterns along different directions. The TIP system should open up avenues for functional imaging of the GI tract in conscious animals in natural physiological states., Current preclinical imaging of intestine in animal models cannot reveal intestinal dynamics in awake condition. Here the authors report a Transillumination Intestine Projection (TIP) imaging system for free-moving mice, and showed the intestine dynamics in conscious animal in natural physiological states.