High-resolution optoacoustic imaging of tissue responses to vascular-targeted therapies

Unsupervised Segmentation of 3D Microvascular Photoacoustic Images Using Deep Generative Learning

Mesoscopic photoacoustic imaging (PAI) enables label-free visualization of vascular networks in tissues with high contrast and resolution. Segmenting these networks from 3D PAI data and interpreting their physiological and pathological significance is crucial yet challenging due to the time-consuming and error-prone nature of current methods. Deep learning offers a potential solution; however, supervised analysis frameworks typically require human-annotated ground-truth labels. To address this, an unsupervised image-to-image translation deep learning model is introduced, the Vessel Segmentation Generative Adversarial Network (VAN-GAN). VAN-GAN integrates synthetic blood vessel networks that closely resemble real-life anatomy into its training process and learns to replicate the underlying physics of the PAI system in order to learn how to segment vasculature from 3D photoacoustic images. Applied to a diverse range of in silico, in vitro, and in vivo data, including patient-derived breast cancer xenograft models and 3D clinical angiograms, VAN-GAN demonstrates its capability to facilitate accurate and unbiased segmentation of 3D vascular networks. By leveraging synthetic data, VAN-GAN reduces the reliance on manual labeling, thus lowering the barrier to entry for high-quality blood vessel segmentation (F1 score: VAN-GAN vs. U-Net = 0.84 vs. 0.87) and enhancing preclinical and clinical research into vascular structure and function.

Vascular regional analysis unveils differential responses to anti-angiogenic therapy in pancreatic xenografts through macroscopic photoacoustic imaging

Pancreatic cancer (PC) is a highly lethal malignancy and the third leading cause of cancer deaths in the U.S. Despite major innovations in imaging technologies, there are limited surrogate radiographic indicators to aid in therapy planning and monitoring. Amongst the various imaging techniques Ultrasound-guided photoacoustic imaging (US-PAI) is a promising modality based on endogenous blood (hemoglobin) and blood oxygen saturation (StO 2 ) contrast to monitor response to anti-angiogenic therapies. Adaptation of US-PAI to the clinical realm requires macroscopic configurations for adequate depth visualization, illuminating the need for surrogate radiographic markers, including the tumoral microvessel density (MVD). In this work, subcutaneous xenografts with PC cell lines AsPC-1 and MIA-PaCa-2 were used to investigate the effects of receptor tyrosine kinase inhibitor (sunitinib) treatment on MVD and StO 2 . Through histological correlation, we have shown that regions of high and low vascular density (HVD and LVD) can be identified through frequency domain filtering of macroscopic PA images which could not be garnered from purely global analysis. We utilized vascular regional analysis (VRA) of treatment-induced StO 2 and total hemoglobin (HbT) changes. VRA as a tool to monitor treatment response allowed us to identify potential timepoints of vascular remodeling, highlighting its ability to provide insights into the TME not only for sunitinib treatment but also other anti-angiogenic therapies.

Near-Infrared Absorbing BODIPY-Xanthene Hybrids for Multiplexed Photoacoustic Imaging

We report a series of ethenylene-bridged D-π-A BODIPY-xanthene hybrid dyes with precisely regulated absorption bands ranging from the far-red to the near-infrared region (NIR, 700-1000 nm) through rational molecular design. These dyes have excellent photoacoustic properties, and their biocompatibility can be significantly improved by facilely introducing water-soluble groups. In vivo two-channel multiplexed photoacoustic imaging demonstrated their high-resolution imaging capabilities, making them promising candidates for future NIR bioimaging applications.

A NIR-II Photoacoustic Probe for High Spatial Quantitative Imaging of Tumor Nitric Oxide in Vivo

Nitric oxide (NO) exhibits both pro- and anti-tumor effects. Therefore, real-time in vivo imaging and quantification of tumor NO dynamics are essential for understanding the conflicting roles of NO played in pathophysiology. The current molecular probes, however, cannot provide high-resolution imaging in deep tissues, making them unsuitable for these purposes. Herein, we designed a photoacoustic probe with an absorption maximum beyond 1000 nm for high spatial quantitative imaging of in vivo tumor NO dynamics. The probe exhibits remarkable sensitivity, selective ratiometric response behavior, and good tumor-targeting abilities, facilitating ratiometric imaging of tumor NO throughout tumor progression in a micron-resolution level. Using the probe as the imaging agent, we successfully quantified NO dynamics in tumor, liver and kidney. We have pinpointed an essential concentration threshold of around 80 nmol/cm3 for NO, which plays a crucial role in the "double-edged-sword" function of NO in tumors. Furthermore, we revealed a reciprocal relationship between the NO concentration in tumors and that in the liver, providing initial insights into the possible NO-mediated communication between tumor and the liver. We believe that the probe will help resolve conflicting aspects of NO biology and guide the design of imaging agents for tumor diagnosis and anti-cancer drug screening.

Microneedle System with Biomarker-Activatable Chromophore as Both Optical Imaging Probe and Anti-bacterial Agent for Combination Therapy of Bacterial-Infected Wounds and Outcome Monitoring

Wounds infected with bacteria, if left untreated, have the potential to escalate into life-threatening conditions, such as sepsis, which is characterized by widespread inflammation and organ damage. A comprehensive approach to treating bacterial-infected wounds, encompassing the control of bacterial infection, biofilm eradication, and inflammation regulation, holds significant importance. Herein, a microneedle (MN) patch (FM@ST MN) has been developed, with silk fibroin (SF) and tannic acid-based hydrogel serving as the matrix. Encapsulated within the MNs are the AIEgen-based activatable probe (FQ-H2O2) and the NLRP3 inhibitor MCC950, serving as the optical reporter/antibacterial agent and the inflammation regulator, respectively. When applied onto bacterial-infected wounds, the MNs in FM@ST MN penetrate bacterial biofilms and gradually degrade, releasing FQ-H2O2 and MCC950. The released FQ-H2O2 responds to endogenously overexpressed reactive oxygen species (H2O2) at the wound site, generating a chromophore FQ-OH which emits noticeable NIR-II fluorescence and optoacoustic signals, enabling real-time imaging for outcome monitoring; and this chromophore also exhibits potent antibacterial capability due to its dual positive charges and shows negligible antibacterial resistance. However, the NLRP3 inhibitor MCC950, upon release, suppresses the activation of NLRP3 inflammasomes, thereby mitigating the inflammation triggered by bacterial infections and facilitating wound healing. Furthermore, SF in FM@ST MN aids in tissue repair and regeneration by promoting the proliferation of epidermal cells and fibroblasts and collagen synthesis. This MN system, free from antibiotics, holds promise as a solution for treating and monitoring bacterially infected wounds without the associated risk of antimicrobial resistance.

Multi-Scale Volumetric Dynamic Optoacoustic and Laser Ultrasound (OPLUS) Imaging Enabled by Semi-Transparent Optical Guidance

Major biological discoveries are made by interrogating living organisms with light. However, the limited penetration of un-scattered photons within biological tissues limits the depth range covered by optical methods. Deep-tissue imaging is achieved by combining light and ultrasound. Optoacoustic imaging exploits the optical generation of ultrasound to render high-resolution images at depths unattainable with optical microscopy. Recently, laser ultrasound has been suggested as a means of generating broadband acoustic waves for high-resolution pulse-echo ultrasound imaging. Herein, an approach is proposed to simultaneously interrogate biological tissues with light and ultrasound based on layer-by-layer coating of silica optical fibers with a controlled degree of transparency. The time separation between optoacoustic and ultrasound signals collected with a custom-made spherical array transducer is exploited for simultaneous 3D optoacoustic and laser ultrasound (OPLUS) imaging with a single laser pulse. OPLUS is shown to enable large-scale anatomical characterization of tissues along with functional multi-spectral imaging of chromophores and assessment of cardiac dynamics at ultrafast rates only limited by the pulse repetition frequency of the laser. The suggested approach provides a flexible and scalable means for developing a new generation of systems synergistically combining the powerful capabilities of optoacoustics and ultrasound imaging in biology and medicine.

Amorphous Albumin Gadolinium-Based Nanoparticles for Ultrahigh-Resolution Magnetic Resonance Angiography

Magnetic resonance angiography (MRA) contrast agents are extensively utilized in clinical practice due to their capability of improving the image resolution and sensitivity. However, the clinically approved MRA contrast agents have the disadvantages of a limited acquisition time window and high dose administration for effective imaging. Herein, albumin-coated gadolinium-based nanoparticles (BSA-Gd) were meticulously developed for in vivo ultrahigh-resolution MRA. Compared to Gd-DTPA, BSA-Gd exhibits a significantly higher longitudinal relaxivity (r1 = 76.7 mM-1 s-1), nearly 16-fold greater than that of Gd-DTPA, and an extended blood circulation time (t1/2 = 40 min), enabling a dramatically enhanced high-resolution imaging of microvessels (sub-200 μm) and low dose imaging (about 1/16 that of Gd-DTPA). Furthermore, the clinically significant fine vessels were successfully mapped in large mammals, including a circle of Willis, kidney and liver vascular branches, tumor vessels, and differentiated arteries from veins using dynamic contrast-enhanced MRA BSA-Gd, and have superior imaging capability and biocompatibility, and their clinical applications hold substantial promise.

Quality control in clinical raster-scan optoacoustic mesoscopy

Optoacoustic (photoacoustic) mesoscopy bridges the gap between optoacoustic microscopy and macroscopy and enables high-resolution visualization deeper than optical microscopy. Nevertheless, as images may be affected by motion and noise, it is critical to develop methodologies that offer standardization and quality control to ensure that high-quality datasets are reproducibly obtained from patient scans. Such development is particularly important for ensuring reliability in applying machine learning methods or for reliably measuring disease biomarkers. We propose herein a quality control scheme to assess the quality of data collected. A reference scan of a suture phantom is performed to characterize the system noise level before each raster-scan optoacoustic mesoscopy (RSOM) measurement. Using the recorded RSOM data, we develop a method that estimates the amount of motion in the raw data. These motion metrics are employed to classify the quality of raw data collected and derive a quality assessment index (QASIN) for each raw measurement. Using simulations, we propose a selection criterion of images with sufficient QASIN, leading to the compilation of RSOM datasets with consistent quality. Using 160 RSOM measurements from healthy volunteers, we show that RSOM images that were selected using QASIN were of higher quality and fidelity compared to non-selected images. We discuss how this quality control scheme can enable the standardization of RSOM images for clinical and biomedical applications.

Shedding light on ultrasound in action: Optical and optoacoustic monitoring of ultrasound brain interventions

Monitoring brain responses to ultrasonic interventions is becoming an important pillar of a growing number of applications employing acoustic waves to actuate and cure the brain. Optical interrogation of living tissues provides a unique means for retrieving functional and molecular information related to brain activity and disease-specific biomarkers. The hybrid optoacoustic imaging methods have further enabled deep-tissue imaging with optical contrast at high spatial and temporal resolution. The marriage between light and sound thus brings together the highly complementary advantages of both modalities toward high precision interrogation, stimulation, and therapy of the brain with strong impact in the fields of ultrasound neuromodulation, gene and drug delivery, or noninvasive treatments of neurological and neurodegenerative disorders. In this review, we elaborate on current advances in optical and optoacoustic monitoring of ultrasound interventions. We describe the main principles and mechanisms underlying each method before diving into the corresponding biomedical applications. We identify areas of improvement as well as promising approaches with clinical translation potential.

Membrane-derived particles shed by PSMA-positive cells function as pro-angiogenic stimuli in tumors

Cell membrane-derived particles (Mp) are rounded membrane-enclosed particles that are shed from tumor cells. Mp are formed from tumor membranes and are capable of tumor targeting and immunotherapeutic agents because they share membrane homology with parental cells; thus, they are under consideration as a drug delivery vehicle. Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein with enzymatic functionality, is highly expressed in Mp and extracellular vesicles (EV) from prostate cancer (PCa) with poor clinical prognosis. Although PSMA expression was previously shown in EV and Mp isolated from cell lines and from the blood of patients with high-grade PCa, no pathophysiological effects have been linked to PCa-derived Mp. Here, we compared Mp from PSMA-expressing (PSMA-Mp) and PSMA-non-expressing (WT-Mp) cells side by side in vitro and in vivo. PSMA-Mp can transfer PSMA and new phenotypic characteristics to the tumor microenvironment. The consequence of PSMA transfer to cells and increased secretion of vascular endothelial growth factor-A (VEGF-A), pro-angiogenic and pro-lymphangiogenic mediators, with increased 4E binding protein 1 (4EBP-1) phosphorylation.

Ultrasound-guided Photoacoustic image Annotation Toolkit in MATLAB (PHANTOM) for preclinical applications

Depth-dependent fluence-compensation in photoacoustic (PA) imaging is paramount for accurate quantification of chromophores from deep tissues. Here we present a user-friendly toolkit named PHANTOM (PHotoacoustic ANnotation TOolkit for MATLAB) that includes a graphical interface and assists in the segmentation of ultrasound-guided PA images. We modelled the light source configuration with Monte Carlo eXtreme and utilized 3D segmented tissues from ultrasound to generate fluence maps to depth compensate PA images. The methodology was used to analyze PA images of phantoms with varying blood oxygenation and results were validated with oxygen electrode measurements. Two preclinical models, a subcutaneous tumor and a calcified placenta, were imaged and fluence-compensated using the PHANTOM toolkit and the results were verified with immunohistochemistry. The PHANTOM toolkit provides scripts and auxiliary functions to enable biomedical researchers not specialized in optical imaging to apply fluence correction to PA images, enhancing accessibility of quantitative PAI for researchers in various fields.

Mechanisms of weight loss-induced remission in people with prediabetes: a post-hoc analysis of the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS)

BACKGROUND

Remission of type 2 diabetes can occur as a result of weight loss and is characterised by liver fat and pancreas fat reduction and recovered insulin secretion. In this analysis, we aimed to investigate the mechanisms of weight loss- induced remission in people with prediabetes.

METHODS

In this prespecified post-hoc analysis, weight loss-induced resolution of prediabetes in the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS) was assessed, and the results were validated against participants from the Diabetes Prevention Program (DPP) study. For PLIS, between March 1, 2012, and Aug 31, 2016, participants were recruited from eight clinical study centres (including seven university hospitals) in Germany and randomly assigned to receive either a control intervention, a standard lifestyle intervention (ie, DPP-based intervention), or an intensified lifestyle intervention for 12 months. For DPP, participants were recruited from 23 clinical study centres in the USA between July 31, 1996, and May 18, 1999, and randomly assigned to receive either a standard lifestyle intervention, metformin, or placebo. In both PLIS and DPP, only participants who were randomly assigned to receive lifestyle intervention or placebo and who lost at least 5% of their bodyweight were included in this analysis. Responders were defined as people who returned to normal fasting plasma glucose (FPG; <5·6 mmol/L), normal glucose tolerance (<7·8 mmol/L), and HbA1c less than 39 mmol/mol after 12 months of lifestyle intervention or placebo or control intervention. Non-responders were defined as people who had FPG, 2 h glucose, or HbA1c more than these thresholds. The main outcomes for this analysis were insulin sensitivity, insulin secretion, visceral adipose tissue (VAT), and intrahepatic lipid content (IHL) and were evaluated via linear mixed models.

FINDINGS

Of 1160 participants recruited to PLIS, 298 (25·7%) had weight loss of 5% or more of their bodyweight at baseline. 128 (43%) of 298 participants were responders and 170 (57%) were non-responders. Responders were younger than non-responders (mean age 55·6 years [SD 9·9] vs 60·4 years [8·6]; p<0·0001). The DPP validation cohort included 683 participants who lost at least 5% of their bodyweight at baseline. Of these, 132 (19%) were responders and 551 (81%) were non-responders. In PLIS, BMI reduction was similar between responders and non-responders (responders mean at baseline 32·4 kg/m2 [SD 5·6] to mean at 12 months 29·0 kg/m2 [4·9] vs non-responders 32·1 kg/m2 [5·9] to 29·2 kg/m2 [5·4]; p=0·86). However, whole-body insulin sensitivity increased more in responders than in non-responders (mean at baseline 291 mL/[min × m2], SD 60 to mean at 12 months 378 mL/[min × m2], 56 vs 278 mL/[min × m2], 62, to 323 mL/[min × m2], 66; p<0·0001), whereas insulin secretion did not differ within groups over time or between groups (responders mean at baseline 175 pmol/mmol [SD 64] to mean at 12 months 163·7 pmol/mmol [60·6] vs non-responders 158·0 pmol/mmol [55·6] to 154·1 pmol/mmol [56·2]; p=0·46). IHL decreased in both groups, without a difference between groups (responders mean at baseline 10·1% [SD 8·7] to mean at 12 months 3·5% [3·9] vs non-responders 10·3% [8·1] to 4·2% [4·2]; p=0·34); however, VAT decreased more in responders than in non-responders (mean at baseline 6·2 L [SD 2·9] to mean at 12 months 4·1 L [2·3] vs 5·7 L [2·3] to 4·5 L [2·2]; p=0·0003). Responders had a 73% lower risk of developing type 2 diabetes than non-responders in the 2 years after the intervention ended.

INTERPRETATION

By contrast to remission of type 2 diabetes, resolution of prediabetes was characterised by an improvement in insulin sensitivity and reduced VAT. Because return to normal glucose regulation (NGR) prevents development of type 2 diabetes, we propose the concept of remission of prediabetes in analogy to type 2 diabetes. We suggest that remission of prediabetes should be the primary therapeutic aim in individuals with prediabetes.

FUNDING

German Federal Ministry for Education and Research via the German Center for Diabetes Research; the Ministry of Science, Research and the Arts Baden-Württemberg; the Helmholtz Association and Helmholtz Munich; the Cluster of Excellence Controlling Microbes to Fight Infections; and the German Research Foundation.

Analysis of tumour oxygenation in model animals on a phosphorescence lifetime based macro-imager

Monitoring of tissue O2 is essential for cancer development and treatment, as hypoxic tumour regions develop resistance to radio- and chemotherapy. We describe a minimally invasive technique for the monitoring of tissue oxygenation in developing grafted tumours, which uses the new phosphorescence lifetime based Tpx3Cam imager. CT26 cells stained with a near-infrared emitting nanoparticulate O2 probe NanO2-IR were injected into mice to produce grafted tumours with characteristic phosphorescence. The tumours were allowed to develop for 3, 7, 10 and 17 days, with O2 imaging experiments performed on live and euthanised animals at different time points. Despite a marked trend towards decreased O2 in dead animals, their tumour areas produced phosphorescence lifetime values between 44 and 47 µs, which corresponded to hypoxic tissue with 5-20 μM O2. After the O2 imaging in animals, confocal Phosphorescence Lifetime Imaging Microscopy was conducted to examine the distribution of NanO2-IR probe in the tumours, which were excised, fixed and sliced for the purpose. The probe remained visible as bright and discrete 'islands' embedded in the tumour tissue until day 17 of tumour growth. Overall, this O2 macro-imaging method using NanO2-IR holds promise for long-term studies with grafted tumours in live animal models, providing quantitative 2D mapping of tissue O2.

In vivo noninvasive systemic myography of acute systemic vasoactivity in female pregnant mice

Altered vasoactivity is a major characteristic of cardiovascular and oncological diseases, and many therapies are therefore targeted to the vasculature. Therapeutics which are selective for the diseased vasculature are ideal, but whole-body selectivity of a therapeutic is challenging to assess in practice. Vessel myography is used to determine the functional mechanisms and evaluate pharmacological responses of vascularly-targeted therapeutics. However, myography can only be performed on ex vivo sections of individual arteries. We have developed methods for implementation of spherical-view photoacoustic tomography for non-invasive and in vivo myography. Using photoacoustic tomography, we demonstrate the measurement of acute vascular reactivity in the systemic vasculature and the placenta of female pregnant mice in response to two vasodilators. Photoacoustic tomography simultaneously captures the significant acute vasodilation of major arteries and detects selective vasoactivity of the maternal-fetal vasculature. Photoacoustic tomography has the potential to provide invaluable preclinical information on vascular response that cannot be obtained by other established methods.

Visualizing vasculature and its response to therapy in the tumor microenvironment

Tumor vasculature plays a critical role in the progression and metastasis of tumors, antitumor immunity, drug delivery, and resistance to therapies. The morphological and functional changes of tumor vasculature in response to therapy take place in a spatiotemporal-dependent manner, which can be predictive of treatment outcomes. Dynamic monitoring of intratumor vasculature contributes to an improved understanding of the mechanisms of action of specific therapies or reasons for treatment failure, leading to therapy optimization. There is a rich history of methods used to image the vasculature. This review describes recent advances in imaging technologies to visualize the tumor vasculature, with a focus on enhanced intravital imaging techniques and tumor window models. We summarize new insights on spatial-temporal vascular responses to various therapies, including changes in vascular perfusion and permeability and immune-vascular crosstalk, obtained from intravital imaging. Finally, we briefly discuss the clinical applications of intravital imaging techniques.

Three Strategies in Engineering Nanomedicines for Tumor Microenvironment-Enabled Phototherapy

Canonical phototherapeutics have several limitations, including a lack of tumor selectivity, nondiscriminatory phototoxicity, and tumor hypoxia aggravation. The tumor microenvironment (TME) is characterized by hypoxia, acidic pH, and high levels of H2 O2 , GSH, and proteases. To overcome the shortcomings of canonical phototherapy and achieve optimal theranostic effects with minimal side effects, unique TME characteristics are employed in the development of phototherapeutic nanomedicines. In this review, the effectiveness of three strategies for developing advanced phototherapeutics based on various TME characteristics is examined. The first strategy involves targeted delivery of phototherapeutics to tumors with the assistance of TME-induced nanoparticle disassembly or surface modification. The second strategy involves near-infrared absorption increase-induced phototherapy activation triggered by TME factors. The third strategy involves enhancing therapeutic efficacy by ameliorating TME. The functionalities, working principles, and significance of the three strategies for various applications are highlighted. Finally, possible challenges and future perspectives for further development are discussed.

Vascularized tumor on a microfluidic chip to study mechanisms promoting tumor neovascularization and vascular targeted therapies

The cascade of events leading to tumor formation includes induction of a tumor supporting neovasculature as a primary hallmark of cancer. Developing vasculature is difficult to evaluate in vivo but can be captured using microfluidic chip technology and patient derived cells. Herein, we established an on chip approach to investigate the mechanisms promoting tumor vascularization and vascular targeted therapies via co-culture of metastatic renal cell carcinoma spheroids and endothelial cells in a 3D environment. Our model permitted real-time, high-resolution observation and assessment of tumor-induced angiogenesis, where endothelial cells sprout towards the tumor and mimic a vascular network. Bevacizumab, an angiogenic inhibitor, disrupted interactions between vessels and tumors, destroying the vascular network. The on chip approach enabled assessment of endothelial cell biology, vessel's functionality, drug delivery, and molecular expression of PSMA. Finally, observations in the vascularized tumor on chip permitted direct and conclusive quantification of this therapy in weeks as opposed to months in a comparable animal model.

Teaser

Vascularized tumor on microfluidic chip provides opportunity to study targeted therapies and improves preclinical drug discovery.

Niche preclinical and clinical applications of photoacoustic imaging with endogenous contrast

In the past decade, photoacoustic (PA) imaging has attracted a great deal of popularity as an emergent diagnostic technology owing to its successful demonstration in both preclinical and clinical arenas by various academic and industrial research groups. Such steady growth of PA imaging can mainly be attributed to its salient features, including being non-ionizing, cost-effective, easily deployable, and having sufficient axial, lateral, and temporal resolutions for resolving various tissue characteristics and assessing the therapeutic efficacy. In addition, PA imaging can easily be integrated with the ultrasound imaging systems, the combination of which confers the ability to co-register and cross-reference various features in the structural, functional, and molecular imaging regimes. PA imaging relies on either an endogenous source of contrast (e.g., hemoglobin) or those of an exogenous nature such as nano-sized tunable optical absorbers or dyes that may boost imaging contrast beyond that provided by the endogenous sources. In this review, we discuss the applications of PA imaging with endogenous contrast as they pertain to clinically relevant niches, including tissue characterization, cancer diagnostics/therapies (termed as theranostics), cardiovascular applications, and surgical applications. We believe that PA imaging's role as a facile indicator of several disease-relevant states will continue to expand and evolve as it is adopted by an increasing number of research laboratories and clinics worldwide.

Photodynamic therapy changes tumour immunogenicity and promotes immune-checkpoint blockade response, particularly when combined with micromechanical priming

Photodynamic therapy (PDT) with redaporfin stimulates colon carcinoma (CT26), breast (4T1) and melanoma (B16F10) cells to display high levels of CD80 molecules on their surfaces. CD80 overexpression amplifies immunogenicity because it increases same cell (cis) CD80:PD-L1 interactions, which (i) disrupt binding of T-cells PD-1 inhibitory receptors with their ligands (PD-L1) in tumour cells, and (ii) inhibit CTLA-4 inhibitory receptors binding to CD80 in tumour cells. In some cancer cells, redaporfin-PDT also increases CTLA-4 and PD-L1 expressions and virtuous combinations between PDT and immune-checkpoint blockers (ICB) depend on CD80/PD-L1 or CD80/CTLA-4 tumour overexpression ratios post-PDT. This was confirmed using anti-CTLA-4 + PDT combinations to increase survival of mice bearing CT26 tumours, and to regress lung metastases observed with bioluminescence in mice with orthotopic 4T1 tumours. However, the primary 4T1 responded poorly to treatments. Photoacoustic imaging revealed low infiltration of redaporfin in the tumour. Priming the primary tumour with high-intensity (~ 60 bar) photoacoustic waves generated with nanosecond-pulsed lasers and light-to-pressure transducers improved the response of 4T1 tumours to PDT. Penetration-resistant tumours require a combination of approaches to respond to treatments: tumour priming to facilitate drug infiltration, PDT for a strong local effect and a change in immunogenicity, and immunotherapy for a systemic effect.

Performance evaluation of mesoscopic photoacoustic imaging

Photoacoustic mesoscopy visualises vascular architecture at high-resolution up to ~3 mm depth. Despite promise in preclinical and clinical imaging studies, with applications in oncology and dermatology, the accuracy and precision of photoacoustic mesoscopy is not well established. Here, we evaluate a commercial photoacoustic mesoscopy system for imaging vascular structures. Typical artefact types are first highlighted and limitations due to non-isotropic illumination and detection are evaluated with respect to rotation, angularity, and depth of the target. Then, using tailored phantoms and mouse models, we investigate system precision, showing coefficients of variation (COV) between repeated scans [short term (1 h): COV= 1.2%; long term (25 days): COV= 9.6%], from target repositioning (without: COV=1.2%, with: COV=4.1%), or from varying in vivo user experience (experienced: COV=15.9%, unexperienced: COV=20.2%). Our findings show robustness of the technique, but also underscore general challenges of limited-view photoacoustic systems in accurately imaging vessel-like structures, thereby guiding users when interpreting biologically-relevant information.

In vivo co-registered hybrid-contrast imaging by successive photoacoustic tomography and magnetic resonance imaging

Magnetic resonance imaging (MRI) and photoacoustic tomography (PAT) offer two distinct image contrasts. To integrate these two modalities, we present a comprehensive hardware-software solution for the successive acquisition and co-registration of PAT and MRI images in in vivo animal studies. Based on commercial PAT and MRI scanners, our solution includes a 3D-printed dual-modality imaging bed, a 3-D spatial image co-registration algorithm with dual-modality markers, and a robust modality switching protocol for in vivo imaging studies. Using the proposed solution, we successfully demonstrated co-registered hybrid-contrast PAT-MRI imaging that simultaneously displays multi-scale anatomical, functional and molecular characteristics on healthy and cancerous living mice. Week-long longitudinal dual-modality imaging of tumor development reveals information on size, border, vascular pattern, blood oxygenation, and molecular probe metabolism of the tumor micro-environment at the same time. The proposed methodology holds promise for a wide range of pre-clinical research applications that benefit from the PAT-MRI dual-modality image contrast.

Transrectal Absorber Guide Raster-Scanning Optoacoustic Mesoscopy for Label-Free In Vivo Assessment of Colitis

Optoacoustic imaging (OAI) enables microscale imaging of endogenous chromophores such as hemoglobin at significantly higher penetration depths compared to other optical imaging technologies. Raster-scanning optoacoustic mesoscopy (RSOM) has recently been shown to identify superficial microvascular changes associated with human skin pathologies. In animal models, the imaging depth afforded by RSOM can enable entirely new capabilities for noninvasive imaging of vascular structures in the gastrointestinal tract, but exact localization of intra-abdominal organs is still elusive. Herein the development and application of a novel transrectal absorber guide for RSOM (TAG-RSOM) is presented to enable accurate transabdominal localization and assessment of colonic vascular networks in vivo. The potential of TAG-RSOM is demonstrated through application during mild and severe acute colitis in mice. TAG-RSOM enables visualization of transmural vascular networks, with changes in colon wall thickness, blood volume, and OAI signal intensities corresponding to colitis-associated inflammatory changes. These findings suggest TAG-RSOM can provide a novel monitoring tool in preclinical IBD models, refining animal procedures and underlines the capabilities of such technologies to address inflammatory bowel diseases in humans.

Pyrrolopyrrole aza-BODIPY-based NIR-II fluorophores for in vivo dynamic vascular dysfunction visualization of vascular-targeted photodynamic therapy

Real-time monitoring vascular responses is crucial for evaluating the therapeutic effects of vascular-targeted photodynamic therapy (V-PDT). Herein, we developed a highly-stable and bright aggregation induced emission (AIE) fluorophore (PTPE3 NP) for dynamic fluorescence (FL) imaging of vascular dysfunction beyond 1300 nm window during V-PDT. The superior brightness (ϵ_maxΦ_{f>1000 nm} ≈ 180.05 M^-1 cm^-1) and high resolution of PTPE3 NP affords not only high-clarity images of whole-body and local vasculature (hindlimbs, mesentery, and tumor) but also high-speed video imaging for tracking blood circulation process. By virtue of the NPs' prolonged blood circulation time (t_1/2 ≈ 86.5 min) and excellent photo/chemical (pH, RONS) stability, mesenteric and tumor vascular dysfunction (thrombosis formation, vessel occlusion, and hemorrhage) can be successfully visualized during V-PDT by FL imaging for the first time. Furthermore, the reduction of blood flow velocity (BFV) can be monitored in real time for precisely evaluating efficacy of V-PDT. These provide a powerful approach for assessing vascular responses during V-PDT and promote the development of advanced fluorophores for biological imaging.

Use of photoacoustic imaging for monitoring vascular disrupting cancer treatments

Vascular disrupting agents disrupt tumor vessels, blocking the nutritional and oxygen supply tumors need to thrive. This is achieved by damaging the endothelium lining of blood vessels, resulting in red blood cells (RBCs) entering the tumor parenchyma. RBCs present in the extracellular matrix are exposed to external stressors resulting in biochemical and physiological changes. The detection of these changes can be used to monitor the efficacy of cancer treatments. Spectroscopic photoacoustic (PA) imaging is an ideal candidate for probing RBCs due to their high optical absorption relative to surrounding tissue. The goal of this work is to use PA imaging to monitor the efficacy of the vascular disrupting agent 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) through quantitative analysis. Then, 4T1 breast cancer cells were injected subcutaneously into the left hind leg of eight BALB/c mice. After 10 days, half of the mice were treated with 15 mg/kg of DMXAA and the other half were injected with saline. All mice were imaged using the VevoLAZR X PA system before treatment, 24 and 72 hours after treatment. The imaging was done at six wavelengths and linear spectral unmixing was applied to the PA images to quantify three forms of hemoglobin (oxy, deoxy and met-hemoglobin). After imaging, tumors were histologically processed and H&E and TUNEL staining were used to detect the tissue damage induced by the DMXAA treatment. The total hemoglobin concentration remained unchanged after treatment for the saline treated mice. For DMXAA treated mice, a 10% increase of deoxyhemoglobin concentration was detected 24 hours after treatment and a 22.6% decrease in total hemoglobin concentration was observed by 72 hours. A decrease in the PA spectral slope parameters was measured 24 hours after treatment. This suggests that DMXAA induces vascular damage, causing red blood cells to extravasate. Furthermore, H&E staining of the tumor showed areas of bleeding with erythrocyte deposition. These observations are further supported by the increase in TUNEL staining in DMXAA treated tumors, revealing increased cell death due to vascular disruption. This study demonstrates the capability of PA imaging to monitor tumor vessel disruption by the vascular disrupting agent DMXAA.

Blood-Brain Barrier Permeable Photoacoustic Probe for High-Resolution Imaging of Nitric Oxide in the Living Mouse Brain

Alternations in the brain nitric oxide (NO) homeostasis are associated with a variety of neurodegeneration diseases; therefore, high-resolution imaging of NO in the brain is essential for understanding pathophysiological processes. However, currently available NO probes are unsuitable for this purpose due to their poor ability to cross the blood-brain barrier (BBB) or to image in deep tissues with spatial resolution. Herein, we developed a photoacoustic (PA) probe with BBB crossing ability to overcome this obstacle. The probe shows a highly selective ratiometric response toward NO, which enables the probe to image NO with micron resolution in the whole brain of living mice. Using three-dimensional PA imaging, we demonstrated that the probe could be used to visualize the detailed NO distribution in varying depth cross-sections (0-8 mm) of the living Parkinson's disease (PD) mouse brain. We also investigated the therapeutic properties of natural polyphenols in the PD mouse brain using the probe as an imaging agent and suggested the potential of the probe for screening therapeutic agents. This study provides a promising imaging agent for imaging of NO in the mouse brain with high resolution. We anticipate that these findings may open up new possibilities for understanding the biological functions of NO in the brain and the development of new imaging agents for the diagnosis and treatment of brain diseases.

A Photoacoustic Probe with Blood-Brain Barrier Crossing Ability for Imaging Oxidative Stress Dynamics in the Mouse Brain

Spatiotemporal assessment of the oxidative stress dynamics in the brain is crucial for understanding the molecular mechanism underlying neurodegenerative diseases. However, existing oxidative stress probes have poor blood-brain barrier permeability or poor penetration depth, making them unsuitable for brain imaging. Herein, we developed a photoacoustic probe that enables real-time imaging of oxidative stress dynamics in the mouse brain. The probe not only responds to oxidative stress in a reversible and ratiometric manner, but it can also cross the blood-brain barrier of the mouse brain. Notably, the probe displayed excellent photoacoustic imaging of oxidative stress dynamics in the brains of Parkinson's disease mouse models. In addition, we investigated the antioxidant properties of natural polyphenols in the brain of a Parkinson's disease mouse model using the probe as an imaging agent and suggested the potential of the probe for screening anti-oxidative stress agents.

Fabrication of magnetic nanoprobes for ultrahigh-field magnetic resonance imaging

Ultrahigh-field magnetic resonance imaging (UHF-MRI) has been attracting tremendous attention in biomedical imaging owing to its high signal-to-noise ratio, superior spatial resolution, and fast imaging speed. However, at UHF-MRI, there is a lack of proper imaging probes that can impart superior imaging sensitivity of disease lesions because conventional contrast agents generally produce pronounced susceptibility artifacts and induce very strong T₂ decay effects, thus hindering satisfactory imaging performance. This review focused on the recent development of high-performance nanoprobes that can improve the sensitivity and specificity of UHF-MRI. Firstly, the contrast enhancement mechanism of nanoprobes at UHF-MRI has been elucidated. In particular, the strategies for modulating nanoprobe performance, including size effects, metal alloying and magnetic-dopant effects, surface effects, and stimuli-response regulation, have been comprehensively discussed. Furthermore, we illustrate the remarkable advances in the design of UHF-MRI nanoprobes for medical diagnosis, such as early-stage primary tumor and metastasis imaging, angiography, and dynamic monitoring of biosignaling factors in vivo. Finally, we provide a summary and outlook on the development of cutting-edge UHF-MRI nanoprobes for advanced biomedical imaging.

Discovery of BODIPY J-aggregates with absorption maxima beyond 1200 nm for biophotonics

Organic dyes with absorption maxima in the second near-infrared window (NIR-II; 1000 to 1700 nm) are of great interest in biophotonics. However, because of the lack of appropriate molecular scaffolds, current research in this field is limited to cyanine dyes, and developing NIR-II-absorbing organic dyes for biophotonics remains an immense challenge. Here, we rationally designed an ethenylene-bridged BODIPY scaffold featuring excellent J-aggregation capabilities and revealed that the bridging ethylene unit is crucial for intermolecular J-coupling regulation. By integrating the electron-donating groups into the scaffold, we obtained a BODIPY dye, BisBDP2, with a J-aggregate absorption maximum of around 1300 nm. BisBDP2 J-aggregates show excellent photothermal performance, including intense photoacoustic response, and a high photothermal conversion efficiency value of 63%. In vivo results demonstrate the potential of J-aggregates for photoacoustic imaging and photothermal ablation of deep-seated tumors. This study will speed up the exploration of NIR-II-absorbing J-aggregates for future biophotonic applications.

3D imaging of vascular anomalies using raster-scanning optoacoustic mesoscopy

OBJECTIVES

Vascular anomalies such as capillary malformations (CMs) and infantile hemangiomas (IHs) are common pediatric vascular disorders that are treated with therapeutic laser. The treatment method, however, relies on subjective evaluation of clinical findings and can have unpredictable results. Raster-scanning optoacoustic mesoscopy (RSOM) is an innovative imaging technology using pulsed-light laser to excite hemoglobin, generating ultrasound waves that are converted into three-dimensional images of tissues. RSOM can provide objective information about superficial structures such as the microvasculature of vascular anomalies.

MATERIALS AND METHODS

In this study, we explore the clinical potential of RSOM to study vascular anomalies before and after laser treatment. We scanned nine patients with CM (n = 6) and IH (n = 3) who underwent laser treatment and calculated the blood vessel volume.

RESULTS

Overall, there was a posttreatment volume increase in CM, and a decrease in IH.

CONCLUSION

These findings support the possibility that RSOM may have a role in developing an objective method of evaluating these lesions, leading to a tailored treatment approach and avoidance of adverse outcomes.

In vivo monitoring of vascularization and oxygenation of tumor xenografts using optoacoustic microscopy and diffuse optical spectroscopy

The research is devoted to comparison of the blood vessel structure and the oxygen state of three xenografts: SN-12C, HCT-116 and Colo320. Differences in the vessel formation and the level of oxygenation are revealed by optoacoustic (OA) microscopy and diffuse optical spectroscopy (DOS) respectively. The Colo320 tumor is characterized by the highest values of vessel size and fraction. DOS showed increased content of deoxyhemoglobin that led to reduction of saturation level for Colo320 as compared to other tumors. Immunohistochemical (IHC) analysis for CD31 demonstrates the higher number of vessels in Colo320. The IHC for hypoxia was consistent with DOS results and revealed higher values of the relative hypoxic fraction in Colo320.

The sound of drug delivery: Optoacoustic imaging in pharmacology

Optoacoustic (photoacoustic) imaging offers unique opportunities for visualizing biological function in vivo by achieving high-resolution images of optical contrast much deeper than any other optical technique. The method detects ultrasound waves that are generated inside tissue by thermo-elastic expansion, i.e., the conversion of light absorption by tissue structures to ultrasound when the tissue is illuminated by the light of varying intensity. Listening instead of looking to light offers the major advantage of image formation with a resolution that obeys ultrasonic diffraction and not photon diffusion laws. While the technique has been widely used to explore contrast from endogenous photo-absorbing molecules, such as hemoglobin or melanin, the use of exogenous agents can extend applications to a larger range of biological and possible clinical applications, such as image-guided surgery, disease monitoring, and the evaluation of drug delivery, biodistribution, and kinetics. This review summarizes recent developments in optoacoustic agents, and highlights new functions visualized and potent pharmacology applications enabled with the use of external contrast agents.

High-resolution label-free mapping of murine kidney vasculature by raster-scanning optoacoustic mesoscopy: an ex vivo study

BACKGROUND

Chronic kidney disease (CKD) is a global burden affecting both children and adults. Novel imaging modalities hold great promise to visualize and quantify structural, functional, and molecular organ damage. The aim of the study was to visualize and quantify murine renal vasculature using label-free raster scanning optoacoustic mesoscopy (RSOM) in explanted organs from mice with renal injury.

MATERIAL AND METHODS

For the experiments, freshly bisected kidneys of alpha 8 integrin knock-out (KO) and wildtype mice (WT) were used. A total of n=7 female (n=4 KO, n=3 WT) and n=6 male animals (n=2 KO, n=4 WT) aged 6 weeks were examined with RSOM optoacoustic imaging systems (RSOM Explorer P50 at SWL 532nm and/or ms-P50 imaging system at 532 nm, 555 nm, 579 nm, and 606 nm). Images were reconstructed using a dedicated software, analyzed for size and vascular area and compared to standard histologic sections.

RESULTS

RSOM enabled mapping of murine kidney size and vascular area, revealing differences between kidney sizes of male (m) and female (f) mice (merged frequencies (MF) f vs. m: 52.42±6.24 mm² vs. 69.18±15.96 mm², p=0.0156) and absolute vascular area (MF f vs. m: 35.67±4.22 mm² vs. 49.07±13.48 mm², p=0.0036). Without respect to sex, the absolute kidney area was found to be smaller in knock-out (KO) than in wildtype (WT) mice (WT vs. KO: MF: p=0.0255) and showed a similar trend for the relative vessel area (WT vs. KO: MF p=0.0031). Also the absolute vessel areas of KO compared to WT were found significantly different (MF p=0.0089). A significant decrease in absolute vessel area was found in KO compared to WT male mice (MF WT vs. KO: 54.37±9.35 mm² vs. 34.93±13.82 mm², p=0.0232). In addition, multispectral RSOM allowed visualization of oxygenated and deoxygenated parenchymal regions by spectral unmixing.

CONCLUSION

This study demonstrates the capability of RSOM for label-free visualization of differences in vascular morphology in ex vivo murine renal tissue at high resolution. Due to its scalability optoacoustic imaging provides an emerging modality with potential for further preclinical and clinical imaging applications.

Light-triggered photodynamic nanomedicines for overcoming localized therapeutic efficacy in cancer treatment

Photodynamic nanomedicines have significantly enhanced the therapeutic efficacy of photosensitizers (PSs) by overcoming critical limitations of PSs such as poor water solubility and low tumor accumulation. Furthermore, functional photodynamic nanomedicines have enabled overcoming oxygen depletion during photodynamic therapy (PDT) and tissue light penetration limitation by supplying oxygen or upconverting light in targeted tumor tissues, resulting in providing the potential to overcome biological therapeutic barriers of PDT. Nevertheless, their localized therapeutic effects still remain a huddle for the effective treatment of metastatic- or recurrent tumors. Recently, newly designed photodynamic nanomedicines and their combination chemo- or immune checkpoint inhibitor therapy enable the systemic treatment of various metastatic tumors by eliciting antitumor immune responses via immunogenic cell death (ICD). This review introduces recent advances in photodynamic nanomedicines and their applications, focusing on overcoming current limitations. Finally, the challenges and future perspectives of the clinical translation of photodynamic nanomedicines in cancer PDT are discussed.

Quantification of vascular networks in photoacoustic mesoscopy

Mesoscopic photoacoustic imaging (PAI) enables non-invasive visualisation of tumour vasculature. The visual or semi-quantitative 2D measurements typically applied to mesoscopic PAI data fail to capture the 3D vessel network complexity and lack robust ground truths for assessment of accuracy. Here, we developed a pipeline for quantifying 3D vascular networks captured using mesoscopic PAI and tested the preservation of blood volume and network structure with topological data analysis. Ground truth data of in silico synthetic vasculatures and a string phantom indicated that learning-based segmentation best preserves vessel diameter and blood volume at depth, while rule-based segmentation with vesselness image filtering accurately preserved network structure in superficial vessels. Segmentation of vessels in breast cancer patient-derived xenografts (PDXs) compared favourably to ex vivo immunohistochemistry. Furthermore, our findings underscore the importance of validating segmentation methods when applying mesoscopic PAI as a tool to evaluate vascular networks in vivo.

Multispectral optoacoustic tomography for in vivo detection of lymph node metastases in oral cancer patients using an EGFR-targeted contrast agent and intrinsic tissue contrast: A proof-of-concept study

Oral cancer patients undergo diagnostic surgeries to detect occult lymph node metastases missed by preoperative structural imaging techniques. Reducing these invasive procedures that are associated with considerable morbidity, requires better preoperative detection. Multispectral optoacoustic tomography (MSOT) is a rapidly evolving imaging technique that may improve preoperative detection of (early-stage) lymph node metastases, enabling the identification of molecular changes that often precede structural changes in tumorigenesis. Here, we characterize the optoacoustic properties of cetuximab-800CW, a tumor-specific fluorescent tracer showing several photophysical properties that benefit optoacoustic signal generation. In this first clinical proof-of-concept study, we explore its use as optoacoustic to differentiate between malignant and benign lymph nodes. We characterize the appearance of malignant lymph nodes and show differences in the distribution of intrinsic chromophores compared to benign lymph nodes. In addition, we suggest several approaches to improve the efficiency of follow-up studies.

Fast raster-scan optoacoustic mesoscopy enables assessment of human melanoma microvasculature in vivo

Melanoma is associated with angiogenesis and vascular changes that may extend through the entire skin depth. Three-dimensional imaging of vascular characteristics in skin lesions could therefore allow diagnostic insights not available by conventional visual inspection. Raster-scan optoacoustic mesoscopy (RSOM) images microvasculature through the entire skin depth with resolutions of tens of micrometers; however, current RSOM implementations are too slow to overcome the strong breathing motions on the upper torso where melanoma lesions commonly occur. To enable high-resolution imaging of melanoma vasculature in humans, we accelerate RSOM scanning using an illumination scheme that is coaxial with a high-sensitivity ultrasound detector path, yielding 15 s single-breath-hold scans that minimize motion artifacts. We apply this Fast RSOM to image 10 melanomas and 10 benign nevi in vivo, showing marked differences between malignant and benign lesions, supporting the possibility to use biomarkers extracted from RSOM imaging of vasculature for lesion characterization to improve diagnostics.

Raster-Scanning-Optoacoustic Mesoscopy can be used to image the vasculature in skin cancer lesions but is limited by a long exposure time. Here; the authors increase the speed of the imaging using co-axial illumination and a high-sensitivity ultrasound detector path.

Subtractive manufacturing with swelling induced stochastic folding of sacrificial materials for fabricating complex perfusable tissues in multi-well plates

Organ-on-a-chip systems that recapitulate tissue-level functions have been proposed to improve in vitro-in vivo correlation in drug development. Significant progress has been made to control the cellular microenvironment with mechanical stimulation and fluid flow. However, it has been challenging to introduce complex 3D tissue structures due to the physical constraints of microfluidic channels or membranes in organ-on-a-chip systems. Inspired by 4D bioprinting, we develop a subtractive manufacturing technique where a flexible sacrificial material can be patterned on a 2D surface, swell and shape change when exposed to aqueous hydrogel, and subsequently degrade to produce perfusable networks in a natural hydrogel matrix that can be populated with cells. The technique is applied to fabricate organ-specific vascular networks, vascularized kidney proximal tubules, and terminal lung alveoli in a customized 384-well plate and then further scaled to a 24-well plate format to make a large vascular network, vascularized liver tissues, and for integration with ultrasound imaging. This biofabrication method eliminates the physical constraints in organ-on-a-chip systems to incorporate complex ready-to-perfuse tissue structures in an open-well design.

Renal Artery Catheterization for Microcapsules' Targeted Delivery to the Mouse Kidney

The problem of reducing the side effects associated with drug distribution throughout the body in the treatment of various kidney diseases can be solved by effective targeted drug delivery. The method described herein involves injection of a drug encapsulated in polyelectrolyte capsules to achieve prolonged local release and long-term capillary retention of several hours while these capsules are administered via the renal artery. The proposed method does not imply disruption (puncture) of the renal artery or aorta and is suitable for long-term chronic experiments on mice. In this study, we compared how capsule size and dosage affect the target kidney blood flow. It has been established that an increase in the diameter of microcapsules by 29% (from 3.1 to 4.0 μm) requires a decrease in their concentration by at least 50% with the same suspension volume. The photoacoustic method, along with laser speckle contrast imaging, was shown to be useful for monitoring blood flow and selecting a safe dose. Capsules contribute to a longer retention of a macromolecular substance in the target kidney compared to its free form due to mechanical retention in capillaries and slow impregnation into surrounding tissues during the first 1-3 h, which was shown by fluorescence tomography and microscopy. At the same time, the ability of capillaries to perform almost complete "self-cleaning" from capsular shells during the first 12 h leads to the preservation of organ tissues in a normal state. The proposed strategy, which combines endovascular surgery and the injection of polymer microcapsules containing the active substance, can be successfully used to treat a wide range of nephropathies.

Self-delivery nanomedicine for vascular disruption-supplemented chemo-photodynamic tumor therapy

Tumor vascular blockade is a promising strategy for adjuvant cancer treatment. In this work, a self-delivery nanomedicine is developed based on a vascular disruptor and photosensitizer for tumor synergistic therapy. Specifically, this nanomedicine (designated as CeCA) is comprised of combretastatin A4 (CA4) and chlorine e6 (Ce6) by self-assembly technique. Among which, CA4 could not only induce tubulin inhibition for chemotherapy but also disrupt the vasculature to cause tumor hemorrhage. Moreover, Ce6 is able to generate lots of singlet oxygen (¹O₂) for synergistic photodynamic therapy (PDT) under light irradiation. It is interesting that the carrier-free CeCA possessed a favorable stability and an improved cellular uptake behavior. After intravenous administration, CeCA prefers to accumulate at tumor site for vascular disruption-supplemented chemo-photodynamic therapy. Notably, CeCA is prepared without additional carriers, which avoids the system toxicity raised by excipients. Consequently, CeCA greatly inhibits the tumor growth and leads to a low side effect in vivo. It might open a window in the development of self-supplementary nanomedicine for synergistic tumor treatment.

Noninvasive optoacoustic microangiography reveals dose and size dependency of radiation-induced deep tumor vasculature remodeling

Tumor microvascular responses may provide a sensitive readout indicative of radiation therapy efficacy, its time course and dose dependencies. However, direct high-resolution observation and longitudinal monitoring of large-scale microvascular remodeling in deep tissues remained challenging with the conventional microscopy approaches.

We report on a non-invasive longitudinal study of morphological and functional neovascular responses by means of scanning optoacoustic (ОА) microangiography. In vivo imaging of CT26 tumor response to a single irradiation at varying dose (6, 12, and 18 Gy) has been performed over ten days following treatment. Tumor oxygenation levels were further estimated using diffuse optical spectroscopy (DOS) with a contact fiber probe.

OA revealed the formation of extended vascular structures on the whole tumor scale during its proliferation, whereas only short fragmented vascular regions were identified following irradiation. On the first day post treatment, a decrease in the density of small (capillary-sized) and medium-sized vessels was revealed, accompanied by an increase in their fragmentation. Larger vessels exhibited an increase in their density accompanied by a decline in the number of vascular segments. Short-lasting response has been observed after 6 and 12 Gy irradiations, whereas 18 Gy treatment resulted in prolonged responses, up to the tenth day after irradiation. DOS measurements further revealed a delayed increase of tumor oxygenation levels for 18 Gy irradiations, commencing on the sixth day post treatment. The ameliorated oxygenation is attributed to diminished oxygen consumption by inhibited tumor cells but not to the elevation of oxygen supply.

This work is the first to demonstrate the differential (size-dependent) nature of vascular responses to radiation treatments at varying doses in vivo. The OA approach thus facilitates the study of radiation-induced vascular changes in an unperturbed in vivo environment while enabling deep tissue high-resolution observations at the whole tumor scale.

High relaxivity Gd3+-based organic nanoparticles for efficient magnetic resonance angiography

Contrast-enhanced MR angiography (MRA) is a critical technique for vascular imaging. Nevertheless, the efficacy of MRA is often limited by the low rate of relaxation, short blood-circulation time, and metal ion-released potential long-term toxicity of clinical available Gd-based contrast agents. In this work, we report a facile and efficient strategy to achieve Gd-chelated organic nanoparticles with high relaxivity for T₁-weighted MRA imaging. The Gd-chelated PEG-TCPP nanoparticles (GPT NPs) have been engineered composite structured consisting of Gd-chelated TCPP and PEG. The spherical structure of TCPP offers more chemical sites for Gd³⁺ coordination to improve the relaxivity and avoid leakage of the Gd³⁺ ions. The synthesized GPT NPs exhibit a high relaxation rate of 35.76 mM^− 1 s^− 1 at 3.0 T, which is higher than the rates for most reported MR contrast agents. Therefore, GPT NPs can be used for MRA with much stronger vascular signals, longer circulation time, and high-resolution arterial vascular visualization than those using clinical MR contrast agents at the same dose. This work may make the T₁ MRI contrast agents for high-resolution angiography possible and offer a new candidate for preclinical and clinical applications of MR vascular imaging and vascular disease diagnosis.

Advanced high resolution three-dimensional imaging to visualize the cerebral neurovascular network in stroke

As an important method to accurately and timely diagnose stroke and study physiological characteristics and pathological mechanism in it, imaging technology has gone through more than a century of iteration. The interaction of cells densely packed in the brain is three-dimensional (3D), but the flat images brought by traditional visualization methods show only a few cells and ignore connections outside the slices. The increased resolution allows for a more microscopic and underlying view. Today's intuitive 3D imagings of micron or even nanometer scale are showing its essentiality in stroke. In recent years, 3D imaging technology has gained rapid development. With the overhaul of imaging mediums and the innovation of imaging mode, the resolution has been significantly improved, endowing researchers with the capability of holistic observation of a large volume, real-time monitoring of tiny voxels, and quantitative measurement of spatial parameters. In this review, we will summarize the current methods of high-resolution 3D imaging applied in stroke.

Graphene-containing metal-organic framework nanocomposites for enhanced microwave ablation of salivary adenoid cystic carcinoma

Salivary adenoid cystic carcinoma (SACC), one of the most common malignant tumors in the head and neck region, is characterized by high postoperative recurrence rate and poor prognosis. Microwave (MW) ablation possesses advantages in preserving SACC patients' facial aesthetics and oral function, but unfortunately, it suffers from low therapeutic efficacy due to the limited MW-thermal efficiency. Moreover, the insufficient thermal ablation may aggravate hypoxic state in tumors, which is deleterious to the treatment of residual tumors and aggressive tumors. Hence, MW ablation has been rarely applied in treating head and neck tumors in recent years. To minimize the unfavorable outcomes and maximize the therapeutic effects of MW ablation, a MW sensitizer coupled with a self-sufficient oxygen nanoagent was employed for the first time in MW ablation to treat head and neck tumors. We prepared a graphene-containing metal-organic framework (ZIF67@Gr-PEG), which exhibited excellent MW thermal conversion ability endowed by the incorporated Gr and showed in situ oxygen generation capacity derived from the ZIF67 matrix. In an animal experiment, ZIF67@Gr-PEG-based MW ablation with a temperature up to 66.1 °C exhibited a high tumor ablation rate. More importantly, insufficient MW ablation-induced high expressions of HIF-1α and VEGF were observed in our experiment, whereas the levels of tumor hypoxia and angiogenesis were efficiently decreased in MW ablation with the assistance of ZIF67@Gr-PEG nanocomposites (NCs). Notably, our strategy for MW ablation not only evidences the great potential of ZIF67@Gr-PEG but also promotes the translation of thermotherapeutic graphene from basic research to clinical practice.

360º optoacoustic capsule endoscopy at 50 Hz for esophageal imaging

Gastrointestinal (GI) endoscopy is a common medical diagnostic procedure used for esophageal cancer detection. Current emerging capsule optoacoustic endoscopes, however, suffer from low pulse repetition rates and slow scanning units limit attainable imaging frame rates. Consequently, motion artifacts result in inaccurate spatial mapping and misinterpretation of data. To overcome these limitations, we report a 360^º, 50 Hz frame rate, distal scanning capsule optoacoustic endoscope. The translational capability of the instrument for human GI tract imaging was characterized with an Archimedean spiral phantom consisting of twelve 100 µm sutures, a stainless steel mesh with a pitch of 3 mm and an ex vivo pig esophagus sample. We estimated an imaging penetration depth of ~0.84 mm in vivo by immersing the mesh phantom in intralipid solution to simulate light scattering in human esophageal tissue and validated our findings ex vivo using pig esophagus. This proof-of-concept study demonstrates the translational potential of the proposed video-rate endoscope for human GI tract imaging.

Multi-step deep neural network for identifying subfascial vessels in a dorsal skinfold window chamber model

Automatic segmentation of blood vessels in the dorsal skinfold window chamber (DWSC) model is a prerequisite for the evaluation of vascular-targeted photodynamic therapy (V-PDT) biological response. Recently, deep learning methods have been widely applied in blood vessel segmentation, but they have difficulty precisely identifying the subfascial vessels. This study proposed a multi-step deep neural network, named the global attention-Xnet (GA-Xnet) model, to precisely segment subfascial vessels in the DSWC model. We first used Hough transform combined with a U-Net model to extract circular regions of interest for image processing. GA step was then employed to obtain global feature learning followed by coarse segmentation for the entire blood vessel image. Secondly, the coarse segmentation of blood vessel images from the GA step and the same number of retinal images from the DRIVE datasets were combined as the mixing sample, inputted into the Xnet step to learn the multiscale feature predicting fine segmentation maps of blood vessels. The data show that the accuracy, sensitivity, and specificity for the segmentation of multiscale blood vessels in the DSWC model are 96.00%, 86.27%, 96.47%, respectively. As a result, the subfascial vessels could be accurately identified, and the connectedness of the vessel skeleton is well preserved. These findings suggest that the proposed multi-step deep neural network helps evaluate the short-term vascular responses in V-PDT.

Combined Fluorescence and Optoacoustic Imaging for Monitoring Treatments against CT26 Tumors with Photoactivatable Liposomes

The newly developed multimodal imaging system combining raster-scan optoacoustic (OA) microscopy and fluorescence (FL) wide-field imaging was used for characterizing the tumor vascular structure with 38/50 μm axial/transverse resolution and assessment of photosensitizer fluorescence kinetics during treatment with novel theranostic agents. A multifunctional photoactivatable multi-inhibitor liposomal (PMILs) nano platform was engineered here, containing a clinically approved photosensitizer, Benzoporphyrin derivative (BPD) in the bilayer, and topoisomerase I inhibitor, Irinotecan (IRI) in its inner core, for a synergetic therapeutic impact. The optimized PMIL was anionic, with the hydrodynamic diameter of 131.6 ± 2.1 nm and polydispersity index (PDI) of 0.05 ± 0.01, and the zeta potential between -14.9 ± 1.04 to -16.9 ± 0.92 mV. In the in vivo studies on BALB/c mice with CT26 tumors were performed to evaluate PMILs' therapeutic efficacy. PMILs demonstrated the best inhibitory effect of 97% on tumor growth compared to the treatment with BPD-PC containing liposomes (PALs), 81%, or IRI containing liposomes (L-[IRI]) alone, 50%. This confirms the release of IRI within the tumor cells upon PMILs triggering by NIR light, which is additionally illustrated by FL monitoring demonstrating enhancement of drug accumulation in tumor initiated by PDT in 24 h after the treatment. OA monitoring revealed the largest alterations of the tumor vascular structure in the PMILs treated mice as compared to BPD-PC or IRI treated mice. The results were further corroborated with histological data that also showed a 5-fold higher percentage of hemorrhages in PMIL treated mice compared to the control groups. Overall, these results suggest that multifunctional PMILs simultaneously delivering PDT and chemotherapy agents along with OA and FL multi-modal imaging offers an efficient and personalized image-guided platform to improve cancer treatment outcomes.

Toward Real-Time Giga-Voxel Optoacoustic/Photoacoustic Microscopy: GPU-Accelerated Fourier Reconstruction with Quasi-3D Implementation

We propose a GPU-accelerated implementation of frequency-domain synthetic aperture focusing technique (SAFT) employing truncated regularized inverse k-space interpolation. Our implementation achieves sub-1s reconstruction time for data sizes of up to 100 M voxels, providing more than a tenfold decrease in reconstruction time as compared to CPU-based SAFT. We provide an empirical model that can be used to predict the execution time of quasi-3D reconstruction for any data size given the specifications of the computing system.

Imaging of peripheral vascular malformations - current concepts and future perspectives

Vascular Malformations belong to the spectrum of orphan diseases and can involve all segments of the vascular tree: arteries, capillaries, and veins, and similarly the lymphatic vasculature. The classification according to the International Society for the Study of Vascular Anomalies (ISSVA) is of major importance to guide proper treatment. Imaging plays a crucial role to classify vascular malformations according to their dominant vessel type, anatomical extension, and flow pattern. Several imaging concepts including color-coded Duplex ultrasound/contrast-enhanced ultrasound (CDUS/CEUS), 4D computed tomography angiography (CTA), magnetic resonance imaging (MRI) including dynamic contrast-enhanced MR-angiography (DCE-MRA), and conventional arterial and venous angiography are established in the current clinical routine. Besides the very heterogenous phenotypes of vascular malformations, molecular and genetic profiling has recently offered an advanced understanding of the pathogenesis and progression of these lesions. As distinct molecular subtypes may be suitable for targeted therapies, capturing certain patterns by means of molecular imaging could enhance non-invasive diagnostics of vascular malformations. This review provides an overview of subtype-specific imaging and established imaging modalities, as well as future perspectives of novel functional and molecular imaging approaches. We highlight recent pioneering imaging studies including thermography, positron emission tomography (PET), and multispectral optoacoustic tomography (MSOT), which have successfully targeted specific biomarkers of vascular malformations.