Photoacoustic Imaging Modalities Research Articles

Engineering Cyanine- and Hemicyanine-Based Probes for Optical Imaging of Kidney Diseases.

Molecular optical probes play pivotal roles in in vivo imaging of biomarkers associated to kidney diseases. Relying on structural tunability and high fluorescence quantum yields, versatile optical probes have been constructed on cyanine or hemicyanine-based scaffold in recent years. This review summaries the recent progress on the development of optical probes for imaging of kidney diseases, particularly through near-infrared fluorescence, chemiluminescence and photoacoustic imaging modalities. The chemical design and sensing mechanisms are discussed along with applications in the detection of renal cell carcinoma and acute kidney injury. This progress provides insights and directions for the development of next generation kidney-targeted probes and for pushing their further applications in preclinical and clinical research.

Testbed mimicking intracellular environment for optical-resolution photoacoustic microscopy

Photoacoustic imaging (PAI) represents an innovative method that utilizes optics for transmission and acoustic for sensing. Within the realm of PAI modalities, optical-resolution photoacoustic microscopy (OR-PAM) stands out for its ability to achieve high-resolution cellular and intracellular imaging. However, an optical testbed setup emulating the intracellular environment and accelerating the development of cellular-level OR-PAM systems has not been established. In this study, we present a testbed setup designed to mimic intracellular conditions. Assessment of this testbed setup efficacy involved embedding photoacoustic contrasts and imaging them using an OR-PAM system. The imaging results show that our testbed setup can provide instrumental in accurately measuring photoacoustic signals within an intracellular aqueous environment, avoiding risks of the contamination and degradation of the acoustic transducer.

Photoacoustic imaging of squirrel monkey cortical responses induced by peripheral mechanical stimulation.

Non-human primates (NHPs) are crucial models for studies of neuronal activity. Emerging photoacoustic imaging modalities offer excellent tools for studying NHP brains with high sensitivity and high spatial resolution. In this research, a photoacoustic microscopy (PAM) device was used to provide a label-free quantitative characterization of cerebral hemodynamic changes due to peripheral mechanical stimulation. A 5 × 5 mm area within the somatosensory cortex region of an adult squirrel monkey was imaged. A deep, fully connected neural network was characterized and applied to the PAM images of the cortex to enhance the vessel structures after mechanical stimulation on the forelimb digits. The quality of the PAM images was improved significantly with a neural network while preserving the hemodynamic responses. The functional responses to the mechanical stimulation were characterized based on the improved PAM images. This study demonstrates capability of PAM combined with machine learning for functional imaging of the NHP brain.

Texaphyrin-Based Calcium Sensor for Multimodal Imaging.

The ability to monitor intracellular calcium concentrations using fluorescent probes has led to important insights into biological signaling processes at the cellular level. An important challenge is to relate such measurements to broader patterns of signaling across fields of view that are inaccessible to optical techniques. To meet this need, we synthesized molecular probes that couple calcium-binding moieties to lanthanide texaphyrins, resulting in complexes endowed with a diverse complement of magnetic and photophysical properties. We show that the probes permit intracellular calcium levels to be assessed by fluorescence, photoacoustic, and magnetic resonance imaging modalities and that they are detectable by multimodal imaging in brain tissue. This work thus establishes a route for monitoring signaling processes over a range of spatial and temporal scales.

An ultrasound-activatable platinum prodrug for sono-sensitized chemotherapy

Despite the great success achieved by photoactivated chemotherapy, eradicating deep tumors using external sources with high tissue penetration depth remains a challenge. Here, we present cyaninplatin, a paradigm of Pt(IV) anticancer prodrug that can be activated by ultrasound in a precise and spatiotemporally controllable manner. Upon sono-activation, mitochondria-accumulated cyaninplatin exhibits strengthened mitochondrial DNA damage and cell killing efficiency, and the prodrug overcomes drug resistance as a consequence of combined effects from released Pt(II) chemotherapeutics, the depletion of intracellular reductants, and the burst of reactive oxygen species, which gives rise to a therapeutic approach, namely sono-sensitized chemotherapy (SSCT). Guided by high-resolution ultrasound, optical, and photoacoustic imaging modalities, cyaninplatin realizes the overall theranostics of tumors in vivo with superior efficacy and biosafety. This work highlights the practical utility of ultrasound to precisely activate Pt(IV) anticancer prodrugs for the eradication of deep tumor lesions and broadens the biomedical uses of Pt coordination complexes.

Implementation and Comparison of Three Image Reconstruction Algorithms in FPGA Toward Palm-Size Photoacoustic Tomography

Photoacoustic (PA) imaging has been widely applied in both preclinical and clinical applications. With a significantly increasing number of data acquisition channels, fast high-quality image reconstruction with low-cost for PA imaging is an open challenge. In this paper, we propose a palm-size PAT system, named palmPAT, to achieve miniaturized low-cost PA imaging modality with high performance. To prove the feasibility, Field Programmable Gate Array (FPGA) implementation of PA image reconstruction is performed to achieve high-quality imaging performance with miniaturized size and cost. This FPGA implementation can be easily adapted to widely used algorithms, such as delay-and-sum (DAS) and its variants (e.g. DMAS, DAS-CF). We have performed in-vivo human finger experiments to demonstrate the feasibility and potential. To our best knowledge, this is the first study concentrated on the implementation and comparison of three frequently-used PA image reconstruction algorithms based on FPGA platform.

Single-shot photoacoustic imaging with single-element transducer through a spatiotemporal encoder.

Current photoacoustic (PA) imaging modalities typically require either serial detection with a single-element transducer or parallel detections with an ultrasonic array, indicating a dilemma between system cost and imaging throughput. PA topography through ergodic relay (PATER) was recently developed to address this bottleneck. However, PATER requires object-specific calibration due to varied boundary condition and must be recalibrated through pointwise scanning for each object before measurements, which is time-consuming and severely limits practical application. We aim to develop a new single-shot PA imaging technique that only requires a one-time calibration for imaging different objects using a single-element transducer. We develop an imaging method, PA imaging through a spatiotemporal encoder (PAISE), to address the above issue. The spatial information is effectively coded into unique temporal features by the spatiotemporal encoder, which allows for compressive image reconstruction. An ultrasonic waveguide is proposed as a critical element to guide the PA waves from the object into the prism, which effectively accounts for the varied boundary condition of different objects. We further add irregular-shaped edges on the prism to introduce randomized internal reflections and further facilitate the scrambling of acoustic waves. The proposed technique is validated through comprehensive numerical simulations and experiments, and it is demonstrated that PAISE can successfully overcome the changed boundary condition and can image different samples given a single calibration. The proposed PAISE technique is capable of single-shot widefield PA imaging with a single-element transducer and does not require sample-specific calibration, which successfully overcomes the major limitation of previous PATER technology.

Vision for Ratiometric Nanoprobes: In Vivo Noninvasive Visualization and Readout of Physiological Hallmarks.

Lesion areas are distinguished from normal tissues surrounding them by distinct physiological characteristics. These features serve as biological hallmarks with which targeted biomedical imaging of the lesion sites can be achieved. Although tremendous efforts have been devoted to providing smart imaging probes with the capability of visualizing the physiological hallmarks at the molecular level, the majority of them are merely able to derive anatomical information from the tissues of interest, and thus are not suitable for taking part in in vivo quantification of the biomarkers. Recent advances in chemical construction of advanced ratiometric nanoprobes (RNPs) have enabled a horizon for quantitatively monitoring the biological abnormalities in vivo. In contrast to the conventional probes whose dependency of output on single-signal profiles restricts them from taking part in quantitative practices, RNPs are designed to provide information in two channels, affording a self-calibration opportunity to exclude the analyte-independent factors from the outputs and address the issue. Most of the conventional RNPs have encountered several challenges regarding the reliability and sufficiency of the obtained data for high-performance imaging. In this Review, we have summarized the recent progresses in developing highly advanced RNPs with the capabilities of deriving maximized information from the lesion areas of interest as well as adapting themselves to the complex biological systems in order to minimize microenvironmental-induced falsified signals. To provide a better outlook on the current advanced RNPs, nanoprobes based on optical, photoacoustic, and magnetic resonance imaging modalities for visualizing a wide range of analytes such as pH, reactive species, and different derivations of amino acids have been included. Furthermore, the physicochemical properties of the RNPs, the major constituents of the nanosystems and the analyte recognition mechanisms have been introduced. Moreover, the alterations in the values of the ratiometric signal in response to the analyte of interest as well as the time at which the highest value is achieved, have been included for most of RNPs discussed in this Review. Finally, the challenges as well as future perspectives in the field are discussed.

Barium sulfate and pigment admixture for photoacoustic and x-ray contrast imaging of the gut.

X-ray imaging is frequently used for gastrointestinal imaging. Photoacoustic imaging (PAI) of the gastrointestinal tract is an emerging approach that has been demonstrated for preclinical imaging of small animals. A contrast agent active in both modalities could be useful for imaging applications. We aimed to develop a dual-modality contrast agent comprising an admixture of barium sulfate with pigments that absorb light in the second near-infrared region (NIR-II), for preclinical imaging with both x-ray and PAI modalities. Eleven different NIR-II dyes were evaluated after admixture with a 40% w/v barium sulfate mixture. The resulting NIR-II absorption in the soluble fraction and in the total mixture was characterized. Proof-of-principle imaging studies in mice were carried out. Pigments that produced more uniform suspensions were assessed further for photoacoustic contrast signal at a wavelength of 1064nm that corresponds to the output of the Nd:YAG laser used. Phantom imaging studies demonstrated that the pigment-barium sulfate mixture generated imaging contrast in both x-ray and PAI modalities. The optimal pigment selected for further study was a cyanine tetrafluoroborate salt. Ex-vivo and whole-body mouse imaging demonstrated that photoacoustic and x-ray contrast signals co-localized in the intestines for both imaging modalities. These data demonstrate that commercially-available NIR-II pigments can simply be admixed with barium sulfate to generate a dual-modality contrast agent appropriate for small animal gastrointestinal imaging.

Hybrid Nanoparticles of Citrate-Coated Manganese Ferrite and Gold Nanorods in Magneto-Optical Imaging and Thermal Therapy.

The development of nanomaterials has drawn considerable attention in nanomedicine to advance cancer diagnosis and treatment over the last decades. Gold nanorods (GNRs) and magnetic nanoparticles (MNPs) have been known as commonly used nanostructures in biomedical applications due to their attractive optical properties and superparamagnetic (SP) behaviors, respectively. In this study, we proposed a simple combination of plasmonic and SP properties into hybrid NPs of citrate-coated manganese ferrite (Ci-MnFe2O4) and cetyltrimethylammonium bromide-coated GNRs (CTAB-GNRs). In this regard, two different samples were prepared: the first was composed of Ci-MnFe2O4 (0.4 wt%), and the second contained hybrid NPs of Ci-MnFe2O4 (0.4 wt%) and CTAB-GNRs (0.04 wt%). Characterization measurements such as UV-Visible spectroscopy and transmission electron microscopy (TEM) revealed electrostatic interactions caused by the opposing surface charges of hybrid NPs, which resulted in the formation of small nanoclusters. The performance of the two samples was investigated using magneto-motive ultrasound imaging (MMUS). The sample containing Ci-MnFe2O4_CTAB-GNRs demonstrated a displacement nearly two-fold greater than just using Ci-MnFe2O4; therefore, enhancing MMUS image contrast. Furthermore, the preliminary potential of these hybrid NPs was also examined in magnetic hyperthermia (MH) and photoacoustic imaging (PAI) modalities. Lastly, these hybrid NPs demonstrated high stability and an absence of aggregation in water and phosphate buffer solution (PBS) medium. Thus, Ci-MnFe2O4_CTAB-GNRs hybrid NPs can be considered as a potential contrast agent in MMUS and PAI and a heat generator in MH.

Near-Infrared-Light-Mediated DNA-Logic Nanomachine for Bioorthogonal Cascade Imaging of Endogenous Interconnected MicroRNAs and Metal Ions.

The interconnection of microRNAs (miRNAs) and metal ions governs multiple biological processes in disease development and progression. However, developing multiplexed tools for dynamic imaging of these regulators remains a significant challenge. Herein, we report a conceptual approach for the design of an optically controlled DNA nanomachine by introducing a ternary DNAzyme-based, UV light-cleavable DNA scaffold and upconversion nanoparticle to the activatable hybrid chain reaction. We demonstrate that this nanomachine is capable of being effectively operated either in the presence of an endogenous miRNA target or the coexistence of intracellular Zn2+ and external near-infrared light, resulting in enhanced fluorescence resonance energy transfer signals. With this design, the logic-gated imaging of endogenous miR-21 and Zn2+ is demonstrated in living cells. More importantly, taking advantages of photoacoustic imaging modality, a combinational logic circuit (AND/OR) is constructed for the bioorthogonal cascade imaging of miR-21 and Zn2+ in vivo, realizing dynamic monitoring of the correlation of miRNA and metal ions levels. Collectively, our results suggest that this conceptual design possesses the ability to expand the DNA nanomachine toolbox for visualizing a broad spectrum of interconnected molecules and thus provides new perspectives to improve the diagnostic and therapeutic outcomes.

Emerging photonic technologies for cultural heritage studies: the examples of non-linear optical microscopy and photoacoustic imaging

The availability of non-invasive technologies, which can be used separately or in combination for obtaining chemical composition data and structural information of Cultural Heritage (CH) materials, is of prime importance for improving the understanding the environmental or ageing impact on monuments and artefacts and defining optimal strategies for their conservation. This paper overviews and assesses the potential of two emerging photonic technologies, the Non-linear Optical Microscopy (NLOM) and Photoacoustic (PA) imaging modalities, for a variety of diagnostic applications in preservation science. These techniques, which are well-established in biomedical research, during the last few years have been also investigated as non-invasive tools for the in-depth, high-resolution analysis of various CH objects, including paintings, documents and murals. We discuss on the applicability of these diagnostic optical methods to obtain precise stratigraphic information in artefacts, evaluating additionally the presence and the extent of potential morphological or chemical changes in several CH materials due to ageing. Furthermore, we demonstrate that the contrast complementarity of NLOM and PA imaging provides invaluable insights into the structural integrity of an artwork, which can be subsequently utilized for the early and accurate detection of depth degradation effects.

Photo-acoustic inversion using plasmonic contrast agents: The full Maxwell model

We analyze the inversion of the photo-acoustic imaging modality using electromagnetic plasmonic nano-particles as contrast agents. We prove that the generated pressure, before and after injecting the plasmonic nano-particles, measured at a single point, located away from the targeted inhomogeneity to image, and at a given band of incident frequencies is enough to reconstruct the (eventually complex valued) permittivity. Indeed, from these measurements, we define an indicator function which depends on the used incident frequency and the time of measurement. This indicator function has differentiating behaviors in terms of both time and frequency. First, from the behavior in terms of time, we can estimate the arrival time of the pressure from which we can localize the injected nano-particle. Second, we show that this indicator function has maximum picks at incident frequencies close to the plasmonic resonances. This allows us to estimate these resonances from which we construct the permittivity.To justify these properties, we derive the dominant electric field created by the injected nano-particle when the incident frequency is close to plasmonic resonances. This is done for the full Maxwell system. To this end, we use a natural spectral decomposition of the vector space (L2(D))3 based on the spectra of the Newtonian and the Magnetization operators. As another key argument, we provide the singularity analysis of the Green's tensor of the Maxwell problem with varying permittivity. Such singularity is unusual if compared to the ones of the elliptic case (as the acoustic or elastic models). In addition, we show how the derived approximation of the electric fields propagates, as a source, in the induced pressure with the time.

Fast Fourier Transform-weighted Photoacoustic Imaging by In Vivo Magnetic Alignment of Hybrid Nanorods.

Photoacoustic (PA) imaging uses photon-phonon conversion for high-resolution tomography of biological tissues and functions. Exogenous contrast agents are often added to improve the image quality, but the interference from endogenous molecules diminishes the imaging sensitivity and specificity. We report a background-free PA imaging technique based on the active modulation of PA signals via magnetic alignment of Fe3O4@Au hybrid nanorods. Switching the field direction creates enhanced and deactivated PA imaging modalities, enabling a simple pixel subtraction to effectively minimize background noises. Under an alternating magnetic field, the nanorods exhibit PA signals of coherently periodic changes that can be converted into a sharp peak in a frequency domain via the fast Fourier transform. Automatic pixel-wise screening of nanorod signals performed using a computational algorithm across a time-sequence set of PA images regenerates a background-free PA image with significantly improved contrast, specificity, and fidelity.

Design Principles Governing the Development of Theranostic Anticancer Agents and Their Nanoformulations with Photoacoustic Properties.

The unmet need to develop novel approaches for cancer diagnosis and treatment has led to the evolution of theranostic agents, which usually include, in addition to the anticancer drug, an imaging agent based mostly on fluorescent agents. Over the past few years, a non-invasive photoacoustic imaging modality has been effectively integrated into theranostic agents. Herein, we shed light on the design principles governing the development of theranostic agents with photoacoustic properties, which can be formulated into nanocarriers to enhance their potency. Specifically, we provide an extensive analysis of their individual constituents including the imaging dyes, drugs, linkers, targeting moieties, and their formulation into nanocarriers. Along these lines, we present numerous relevant paradigms. Finally, we discuss the clinical relevance of the specific strategy, as also the limitations and future perspectives, and through this review, we envisage paving the way for the development of theranostic agents endowed with photoacoustic properties as effective anticancer medicines.

Cathespin B‐Initiated Cypate Nanoparticle Formation for Tumor Photoacoustic Imaging

AbstractCathepsin B (CTSB) is a lysosomal protease that is overexpressed in the early stage of many cancer types. Precise evaluation of CTSB expression in vivo may provide a promising method for the early diagnosis of cancers. By virtue of the high‐resolution PA imaging modality, a “smart” photoacoustic (PA) probe Cypate‐CBT, which can self‐assemble to cypate‐containing nanoparticles in response to abundant GSH and CTSB inside tumor cells, was developed for the sensitive and specific detection of CTSB activity. Compared with unmodified Cypate, our probe Cypate‐CBT exhibited a 4.9‐fold or 4.7‐fold PA signal enhancement in CTSB‐overexpressing MDA‐MB‐231 cancer cells or tumors, respectively, revealing intracellular accumulation of the probe after CTSB‐initiated self‐assembly. We expect Cypate‐CBT to be employed as an effective PA imaging agent for clinical diagnosis of cancer at early stages.

Cathespin B-Initiated Cypate Nanoparticle Formation for Tumor Photoacoustic Imaging.

Cathepsin B (CTSB) is a lysosomal protease that is overexpressed in the early stage of many cancer types. Precise evaluation of CTSB expression in vivo may provide a promising method for the early diagnosis of cancers. By virtue of the high-resolution PA imaging modality, a "smart" photoacoustic (PA) probe Cypate-CBT, which can self-assemble to cypate-containing nanoparticles in response to abundant GSH and CTSB inside tumor cells, was developed for the sensitive and specific detection of CTSB activity. Compared with unmodified Cypate, our probe Cypate-CBT exhibited a 4.9-fold or 4.7-fold PA signal enhancement in CTSB-overexpressing MDA-MB-231 cancer cells or tumors, respectively, revealing intracellular accumulation of the probe after CTSB-initiated self-assembly. We expect Cypate-CBT to be employed as an effective PA imaging agent for clinical diagnosis of cancer at early stages.

Recent Progress on Molecular Photoacoustic Imaging with Carbon-Based Nanocomposites.

For biomedical imaging, the interest in noninvasive imaging methods is ever increasing. Among many modalities, photoacoustic imaging (PAI), which is a combination of optical and ultrasound imaging techniques, has received attention because of its unique advantages such as high spatial resolution, deep penetration, and safety. Incorporation of exogenous imaging agents further amplifies the effective value of PAI, since they can deliver other specified functions in addition to imaging. For these agents, carbon-based materials can show a large specific surface area and interesting optoelectronic properties, which increase their effectiveness and have proved their potential in providing a theragnostic platform (diagnosis + therapy) that is essential for clinical use. In this review, we introduce the current state of the PAI modality, address recent progress on PAI imaging that takes advantage of carbon-based agents, and offer a future perspective on advanced PAI systems using carbon-based agents.

Mathematical analysis of the photo-acoustic imaging modality using resonating dielectric nano-particles: The 2D TM-model

We deal with the photoacoustic imaging modality using dielectric nano-particles as contrast agents. Exciting the heterogeneous tissue, localized in a bounded domain Ω, with an electromagnetic wave, at a given incident frequency, creates heat in its surrounding which in turn generates an acoustic pressure wave (or fluctuations). The acoustic pressure can be measured in the accessible region ∂Ω surrounding the tissue of interest. The goal is then to extract information about the optical properties (i.e. the permittivity and conductivity) of this tissue from these measurements. We describe two scenarios. In the first one, we inject single nano-particles while in the second one we inject couples of closely spaced nano-particles (i.e. dimers). From the acoustic pressure measured, before and after injecting the nano-particles (for each scenario), at two single points x1 and x2 of ∂Ω and two single times t1≠t2 such that t1,t2>diam(Ω),(1)we localize the center point z of the single nano-particle and reconstruct the phaseless total field |u0| on that point z (where u0 is the total field in the absence of the nano-particles). Hence, we transform the photoacoustic problem into the inversion of phaseless internal electric fields.(2)we localize the centers z1 and z2 of the injected dimers and reconstruct both the permittivity and the conductivity of the tissue on those points. This is done using dielectric nano-particles enjoying high contrasts of their electric permittivity. These results are possible using frequencies of incidence close to the resonances of the used dielectric nano-particles. These particular frequencies are computable. The error of approximations are given in terms of the scales and the contrasts of the dielectric nano-particles. The results are justified in the 2D TM-model.

Flexible fiber-laser ultrasound sensor for multiscale photoacoustic imaging

Photoacoustic imaging (PAI) is a noninvasive biomedical imaging technology capable of multiscale imaging of biological samples from organs down to cells. Multiscale PAI requires different ultrasound transducers that are flat or focused because the current widely-used piezoelectric transducers are rigid and lack the flexibility to tune their spatial ultrasound responses. Inspired by the rapidly-developing flexible photonics, we exploited the inherent flexibility and low-loss features of optical fibers to develop a flexible fiber-laser ultrasound sensor (FUS) for multiscale PAI. By simply bending the fiber laser from straight to curved geometry, the spatial ultrasound response of the FUS can be tuned for both wide-view optical-resolution photoacoustic microscopy at optical diffraction-limited depth (~1 mm) and photoacoustic computed tomography at optical dissipation-limited depth of several centimeters. A radio-frequency demodulation was employed to get the readout of the beat frequency variation of two orthogonal polarization modes in the FUS output, which ensures low-noise and stable ultrasound detection. Compared to traditional piezoelectrical transducers with fixed ultrasound responses once manufactured, the flexible FUS provides the freedom to design multiscale PAI modalities including wearable microscope, intravascular endoscopy, and portable tomography system, which is attractive to fundamental biological/medical studies and clinical applications.