Simultaneous transrectal ultrasound and photoacoustic human prostate imaging

Repurposing indocyanine green: exploring the potential of an old drug in modern medicine

The repurposing of existing drugs, referred to as theranostics, has made profound impacts on precision medicine. Indocyanine green (ICG), a well-established and clinical dye, has continued to be a star agent, described as a multifunctional molecule with concurrent photo- or sono-sensitiveness capabilities and co-delivery accessibility, showing remarkable potential in the area of unimodal or multimodal imaging-guided therapy of various diseases, leading to the extensive consideration of immediate clinical translations. In this review, we strive to bring the understanding of repurposing performance assessment for ICG into practice by clarifying the relationships between its features and applicability. Specifically, we address the obstacles encountered in the process of developing an ICG repurposing strategy, as well as the noteworthy advancements made in the field of ICG repurposing. We also go into detail about the structure-function correlations of drugs containing ICG and how different structural groups significantly affect the physicochemical properties.

A bi-directional segmentation method for prostate ultrasound images under semantic constraints

Due to the lack of sufficient labeled data for the prostate and the extensive and complex semantic information in ultrasound images, accurately and quickly segmenting the prostate in transrectal ultrasound (TRUS) images remains a challenging task. In this context, this paper proposes a solution for TRUS image segmentation using an end-to-end bidirectional semantic constraint method, namely the BiSeC model. The experimental results show that compared with classic or popular deep learning methods, this method has better segmentation performance, with the Dice Similarity Coefficient (DSC) of 96.74% and the Intersection over Union (IoU) of 93.71%. Our model achieves a good balance between actual boundaries and noise areas, reducing costs while ensuring the accuracy and speed of segmentation.

Simultaneous photoacoustic and ultrasound imaging: A review

Photoacoustic imaging (PAI) is an emerging biomedical imaging technique that combines the advantages of optical and ultrasound imaging, enabling the generation of images with both optical resolution and acoustic penetration depth. By leveraging similar signal acquisition and processing methods, the integration of photoacoustic and ultrasound imaging has introduced a novel hybrid imaging modality suitable for clinical applications. Photoacoustic-ultrasound imaging allows for non-invasive, high-resolution, and deep-penetrating imaging, providing a wealth of image information. In recent years, with the deepening research and the expanding biomedical application scenarios of photoacoustic-ultrasound bimodal systems, the immense potential of photoacoustic-ultrasound bimodal imaging in basic research and clinical applications has been demonstrated, with some research achievements already commercialized. In this review, we introduce the principles, technical advantages, and biomedical applications of photoacoustic-ultrasound bimodal imaging techniques, specifically focusing on tomographic, microscopic, and endoscopic imaging modalities. Furthermore, we discuss the future directions of photoacoustic-ultrasound bimodal imaging technology.

Adaptation of a Clinical High-Frequency Transrectal Ultrasound System for Prostate Photoacoustic Imaging: Implementation and Pre-clinical Demonstration

OBJECTIVE

High-frequency, high-resolution transrectal micro-ultrasound (micro-US: ≥15 MHz) imaging of the prostate is emerging as a beneficial tool for scoring disease risk and accurately targeting biopsies. Adding photoacoustic (PA) imaging to visualize abnormal vascularization and accumulation of contrast agents in tumors has potential for guiding focal therapies. In this work, we describe a new imaging platform that combines a transrectal micro-US system with transurethral light delivery for PA imaging.

METHODS

A clinical transrectal micro-US system was adapted to acquire PA images synchronous to a tunable laser pulse. A transurethral side-firing optical fiber was developed for light delivery. A polyvinyl chloride (PVC)-plastisol phantom was developed and characterized to image PA contrast agents in wall-less channels. After resolution measurement in water, PA imaging was demonstrated in phantom channels with dyes and biodegradable nanoparticle contrast agents called porphysomes. In vivo imaging of a tumor model was performed, with porphysomes administered intravenously.

RESULTS

Photoacoustic imaging data were acquired at 5 Hz, and image reconstruction was performed offline. PA image resolution at a 14-mm depth was 74 and 261 μm in the axial and lateral directions, respectively. The speed of sound in PVC-plastisol was 1383 m/s, and the attenuation was 4 dB/mm at 20 MHz. PA signal from porphysomes was spectrally unmixed from blood signals in the tumor, and a signal increase was observed 3 h after porphysome injection.

CONCLUSION

A combined transrectal micro-US and PA imaging system was developed and characterized, and in vivo imaging demonstrated. High-resolution PA imaging may provide valuable additional information for diagnostic and therapeutic applications in the prostate.

An ultrasensitive and broadband transparent ultrasound transducer for ultrasound and photoacoustic imaging in-vivo

Transparent ultrasound transducers (TUTs) can seamlessly integrate optical and ultrasound components, but acoustic impedance mismatch prohibits existing TUTs from being practical substitutes for conventional opaque ultrasound transducers. Here, we propose a transparent adhesive based on a silicon dioxide-epoxy composite to fabricate matching and backing layers with acoustic impedances of 7.5 and 4-6 MRayl, respectively. By employing these layers, we develop an ultrasensitive, broadband TUT with 63% bandwidth at a single resonance frequency and high optical transparency ( > 80%), comparable to conventional opaque ultrasound transducers. Our TUT maximises both acoustic power and transfer efficiency with maximal spectrum flatness while minimising ringdowns. This enables high contrast and high-definition dual-modal ultrasound and photoacoustic imaging in live animals and humans. Both modalities reach an imaging depth of > 15 mm, with depth-to-resolution ratios exceeding 500 and 370, respectively. This development sets a new standard for TUTs, advancing the possibilities of sensor fusion.

Ultrasound technology assisted colloidal nanocrystal synthesis and biomedical applications

Non-invasive and high spatiotemporal resolution mythologies for the diagnosis and treatment of disease in clinical medicine promote the development of modern medicine. Ultrasound (US) technology provides a non-invasive, real-time, and cost-effective clinical imaging modality, which plays a significant role in chemical synthesis and clinical translation, especially in in vivo imaging and cancer therapy. On the one hand, the US treatment is usually accompanied by cavitation, leading to high temperature and pressure, so-called "hot spot", playing a significant role in sonochemical-based colloidal synthesis. Compared with the classical nucleation synthetic method, the sonochemical synthesis strategy presents high efficiency for the fabrication of colloidal nanocrystals due to its fast nucleation and growth procedure. On the other hand, the US is attractive for in vivo and medical treatment, with applications increasing with the development of novel contrast agents, such as the micro and nano bubbles, which are widely used in neuromodulation, with which the US can breach the blood-brain barrier temporarily and safely, opening a new door to neuromodulation and therapy. In terms of cancer treatment, sonodynamic therapy and US-assisted synergetic therapy show great effects against cancer and sonodynamic immunotherapy present unparalleled potentiality compared with other synergetic therapies. Further development of ultrasound technology can revolutionize both chemical synthesis and clinical translation by improving efficiency, precision, and accessibility while reducing environmental impact and enhancing patient care. In this paper, we review the US-assisted sonochemical synthesis and biological applications, to promote the next generation US technology-assisted applications.

Characterization of adnexal lesions using photoacoustic imaging to improve sonographic O-RADS risk assessment

OBJECTIVE

To assess the impact of photoacoustic imaging (PAI) on the assessment of ovarian/adnexal lesion(s) of different risk categories using the sonographic ovarian-adnexal imaging-reporting-data system (O-RADS) in women undergoing planned oophorectomy.

METHOD

This prospective study enrolled women with ovarian/adnexal lesion(s) suggestive of malignancy referred for oophorectomy. Participants underwent clinical ultrasound (US) examination followed by coregistered US and PAI prior to oophorectomy. Each ovarian/adnexal lesion was graded by two radiologists using the US O-RADS scale. PAI was used to compute relative total hemoglobin concentration (rHbT) and blood oxygenation saturation (%sO2 ) colormaps in the region of interest. Lesions were categorized by histopathology into malignant ovarian/adnexal lesion, malignant Fallopian tube only and several benign categories, in order to assess the impact of incorporating PAI in the assessment of risk of malignancy with O-RADS. Malignant and benign histologic groups were compared with respect to rHbT and %sO2 and logistic regression models were developed based on tumor marker CA125 alone, US-based O-RADS alone, PAI-based rHbT with %sO2 , and the combination of CA125, O-RADS, rHbT and %sO2. Areas under the receiver-operating-characteristics curve (AUC) were used to compare the diagnostic performance of the models.

RESULTS

There were 93 lesions identified on imaging among 68 women (mean age, 52 (range, 21-79) years). Surgical pathology revealed 14 patients with malignant ovarian/adnexal lesion, two with malignant Fallopian tube only and 52 with benign findings. rHbT was significantly higher in malignant compared with benign lesions. %sO2 was lower in malignant lesions, but the difference was not statistically significant for all benign categories. Feature analysis revealed that rHbT, CA125, O-RADS and %sO2 were the most important predictors of malignancy. Logistic regression models revealed an AUC of 0.789 (95% CI, 0.626-0.953) for CA125 alone, AUC of 0.857 (95% CI, 0.733-0.981) for O-RADS only, AUC of 0.883 (95% CI, 0.760-1) for CA125 and O-RADS and an AUC of 0.900 (95% CI, 0.815-0.985) for rHbT and %sO2 in the prediction of malignancy. A model utilizing all four predictors (CA125, O-RADS, rHbT and %sO2 ) achieved superior performance, with an AUC of 0.970 (95% CI, 0.932-1), sensitivity of 100% and specificity of 82%.

CONCLUSIONS

Incorporating the additional information provided by PAI-derived rHbT and %sO2 improves significantly the performance of US-based O-RADS in the diagnosis of adnexal lesions. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Advances in photoacoustic imaging aided by nano contrast agents: special focus on role of lymphatic system imaging for cancer theranostics

Photoacoustic imaging (PAI) is a successful clinical imaging platform for management of cancer and other health conditions that has seen significant progress in the past decade. However, clinical translation of PAI based methods are still under scrutiny as the imaging quality and clinical information derived from PA images are not on par with other imaging methods. Hence, to improve PAI, exogenous contrast agents, in the form of nanomaterials, are being used to achieve better image with less side effects, lower accumulation, and improved target specificity. Nanomedicine has become inevitable in cancer management, as it contributes at every stage from diagnosis to therapy, surgery, and even in the postoperative care and surveillance for recurrence. Nanocontrast agents for PAI have been developed and are being explored for early and improved cancer diagnosis. The systemic stability and target specificity of the nanomaterials to render its theranostic property depends on various influencing factors such as the administration route and physico-chemical responsiveness. The recent focus in PAI is on targeting the lymphatic system and nodes for cancer diagnosis, as they play a vital role in cancer progression and metastasis. This review aims to discuss the clinical advancements of PAI using nanoparticles as exogenous contrast agents for cancer theranostics with emphasis on PAI of lymphatic system for diagnosis, cancer progression, metastasis, PAI guided tumor resection, and finally PAI guided drug delivery.

Dissecting Multiparametric Cerebral Hemodynamics using Integrated Ultrafast Ultrasound and Multispectral Photoacoustic Imaging

Understanding brain-wide hemodynamic responses to different stimuli at high spatiotemporal resolutions can help study neuro-disorders and brain functions. However, the existing brain imaging technologies have limited resolution, sensitivity, imaging depth and provide information about only one or two hemodynamic parameters. To address this, we propose a multimodal functional ultrasound and photoacoustic (fUSPA) imaging platform, which integrates ultrafast ultrasound and multispectral photoacoustic imaging methods in a compact head-mountable device, to quantitatively map cerebral blood volume (CBV), cerebral blood flow (CBF), oxygen saturation (SO2) dynamics as well as contrast agent enhanced brain imaging with high spatiotemporal resolutions. After systematic characterization, the fUSPA system was applied to quantitatively study the changes in brain hemodynamics and vascular reactivity at single vessel resolution in response to hypercapnia stimulation. Our results show an overall increase in brain-wide CBV, CBF, and SO2, but regional differences in singular cortical veins and arteries and a reproducible anti-correlation pattern between venous and cortical hemodynamics, demonstrating the capabilities of the fUSPA system for providing multiparametric cerebrovascular information at high-resolution and sensitivity, that can bring insights into the complex mechanisms of neurodiseases.

Automatic search for photoacoustic marker using automated transrectal ultrasound

Real-time transrectal ultrasound (TRUS) image guidance during robot-assisted laparoscopic radical prostatectomy has the potential to enhance surgery outcomes. Whether conventional or photoacoustic TRUS is used, the robotic system and the TRUS must be registered to each other. Accurate registration can be performed using photoacoustic (PA markers). However, this requires a manual search by an assistant [IEEE Robot. Autom. Lett8, 1287 (2023).10.1109/LRA.2022.3191788]. This paper introduces the first automatic search for PA markers using a transrectal ultrasound robot. This effectively reduces the challenges associated with the da Vinci-TRUS registration. This paper investigated the performance of three search algorithms in simulation and experiment: Weighted Average (WA), Golden Section Search (GSS), and Ternary Search (TS). For validation, a surgical prostate scenario was mimicked and various ex vivo tissues were tested. As a result, the WA algorithm can achieve 0.53°±0.30° average error after 9 data acquisitions, while the TS and GSS algorithm can achieve 0.29 ∘ ± 0.31 ∘ and 0.48°±0.32° average errors after 28 data acquisitions.

Diagnosis of liver fibrosis and liver function reserve through non-invasive multispectral photoacoustic imaging

Liver function reserve (LFR) is the sum of remnant functional hepatic cells after liver injury. In the pathologic process of liver fibrosis (LF), LFR is impaired. LFR assessment can help determine the safe scope of liver resection or drug regimen and predict prognosis of patients with liver disease. Here, we used a photoacoustic imaging (PAI) system to assess LF and LFR in rabbit models. We performed PAI, ultrasound elastography and biopsy for 21 rabbits developing none (n = 6) and LF (n = 15). In vivo indocyanine green (ICG) measurements by PAI showed that LF group presented a significantly attenuated ICG clearance compared to control group, indicating LFR impairment of LF. Another finding was a significantly higher collagen photoacoustic signal intensity value was observed in LF both in vivo and in vitro. Our findings demonstrated that PAI was potentially effective to evaluate LFR and collagen accumulation of LF.

Thirty years of research on photoacoustic imaging in the field of cancer: A scientometric analysis of hotspots, bursts, and research trends

As a novel imaging modality based on photoacoustic effects, photoacoustic imaging (PAI) has shown great potential in biomedical applications, especially in the field of cancer. The purpose of our research was to identify collaborations between different institutions, authors, and countries, and to explore the hotspots and prospects of PAI research in the field of cancer. We downloaded publications on PAI research from the Science Citation Index-Expanded (SCI-E) of the Web of Science Core Collection database. Bibliometric analysis was performed using VOSviewer and CiteSpace software. A total of 2561 papers related to PAI research in the field of cancer were identified. A total of 10,105 authors participated in the PAI study, of which the majority (69.33%) authors participated in only 1 article. China (1638, 63.96%) was the country with the most articles in this field, and the Chinese Academy of Sciences (329, 12.85%) was the most productive institution. ACS Applied Materials & Interfaces (146, 5.70%) was the most productive journal and ACS Nano (7262 co-citations) was the most co-cited journal. Current hot topics of PAI research in the cancer field were the construction and development of multifunctional photoacoustic nanoprobes to achieve the integration of tumor detection and treatment. The application of photoacoustic imaging in the field of cancer is in the vigorous development stage and has a bright prospect. There was a wealth of cooperation between authors, countries, and institutions. Our findings can provide information about the future direction of funding agencies and research groups.

Efficient Photoacoustic Image Synthesis with Deep Learning

Photoacoustic imaging potentially allows for the real-time visualization of functional human tissue parameters such as oxygenation but is subject to a challenging underlying quantification problem. While in silico studies have revealed the great potential of deep learning (DL) methodology in solving this problem, the inherent lack of an efficient gold standard method for model training and validation remains a grand challenge. This work investigates whether DL can be leveraged to accurately and efficiently simulate photon propagation in biological tissue, enabling photoacoustic image synthesis. Our approach is based on estimating the initial pressure distribution of the photoacoustic waves from the underlying optical properties using a back-propagatable neural network trained on synthetic data. In proof-of-concept studies, we validated the performance of two complementary neural network architectures, namely a conventional U-Net-like model and a Fourier Neural Operator (FNO) network. Our in silico validation on multispectral human forearm images shows that DL methods can speed up image generation by a factor of 100 when compared to Monte Carlo simulations with 5×108 photons. While the FNO is slightly more accurate than the U-Net, when compared to Monte Carlo simulations performed with a reduced number of photons (5×106), both neural network architectures achieve equivalent accuracy. In contrast to Monte Carlo simulations, the proposed DL models can be used as inherently differentiable surrogate models in the photoacoustic image synthesis pipeline, allowing for back-propagation of the synthesis error and gradient-based optimization over the entire pipeline. Due to their efficiency, they have the potential to enable large-scale training data generation that can expedite the clinical application of photoacoustic imaging.

Photoacoustic clinical applications: Musculoskeletal and abdominal imaging

Photoacoustic (PA) imaging has been extensively investigated in application in biomedicine over the last decade. This article reviews the motivation, significance, and system configuration of a few ongoing studies of implementing photoacoustic technology in musculoskeletal imaging, abdominal imaging, and interstitial sensing. The review then summarizes the methodologies and latest progress of relevant projects. Finally, we discuss our expectations for the future of translation research in PA imaging.

Functional photoacoustic imaging: from nano- and micro- to macro-scale

Functional photoacoustic imaging is a promising biological imaging technique that offers such unique benefits as scalable resolution and imaging depth, as well as the ability to provide functional information. At nanoscale, photoacoustic imaging has provided super-resolution images of the surface light absorption characteristics of materials and of single organelles in cells. At the microscopic and macroscopic scales. photoacoustic imaging techniques have precisely measured and quantified various physiological parameters, such as oxygen saturation, vessel morphology, blood flow, and the metabolic rate of oxygen, in both human and animal subjects. This comprehensive review provides an overview of functional photoacoustic imaging across multiple scales, from nano to macro, and highlights recent advances in technology developments and applications. Finally, the review surveys the future prospects of functional photoacoustic imaging in the biomedical field.

ICG clearance test based on photoacoustic imaging for assessment of human liver function reserve: An initial clinical study

Liver function reserve (LFR) plays an extensive and important role in patients with liver disease. Indocyanine green (ICG) clearance test is the standard diagnostic approach for LFR evaluation which was performed by spectrophotometry or pulse dye densitometry (PDD). Spectrophotometry is the gold standard, it's invasive and not real-time. PDD is non-invasive, but accuracy of PDD is controversial. Taken spectrophotometry as the reference standard, this study investigated the accuracy of photoacoustic imaging (PAI) method for LFR assessment and compared to PDD in healthy volunteers. The results demonstrated a strong correlation between PAI method and spectrophotometry (r = 0.9649, p < 0.0001). No significant difference was shown in ICG clearance between PAI and spectrophotometry method (rate constant k1 vs. k2, 0.001158 +-0.00042 vs. 0.001491 +- 0.00045, p = 0.0727; half-life t1 vs. t2, 601.2 s vs. 474.4 s, p = 0.1450). These results indicated that PAI may be valuable as a noninvasive, accurate diagnostic tool for LFR assessment in human.

Review on ultrasound-guided photoacoustic imaging for complementary analyses of biological systems in vivo

Photoacoustic imaging has been developed as a new biomedical molecular imaging modality. Due to its similarity to conventional ultrasound imaging in terms of signal detection and image generation, dual-modal photoacoustic and ultrasound imaging has been applied to visualize physiological and morphological information in biological systems in vivo. By complementing each other, dual-modal photoacoustic and ultrasound imaging showed synergistic advances in photoacoustic imaging with the guidance of ultrasound images. In this review, we introduce our recent progresses in dual-modal photoacoustic and ultrasound imaging systems at various scales of study, from preclinical small animals to clinical humans. A summary of the works reveals various strategies for combining the structural information of ultrasound images with the molecular information of photoacoustic images.

Photoacoustic Spectral Analysis for Evaluating the Aggressiveness of Prostate Cancer Labeled by Methylene Blue Polyacrylamide Nanoparticles

Evaluating the aggressiveness of prostate cancer (PCa) is crucial for PCa diagnosis and prognosis. Previously, studies have shown that photoacoustic spectral analysis (PASA) can assess prostate tissue microarchitecture for evaluating the aggressiveness of PCa. In this study, in a transgenic mouse (TRAMP) model of PCa, we utilized methylene blue polyacrylamide nanoparticles (MB PAA NPs) to label the cancer cells in prostate in vivo. MB PAA NPs can specifically target proliferating cancer cells as a contrast agent, allowing photoacoustic (PA) imaging to better detect PCa tumors, and also assessing prostate glandular architecture. With the PA signals from the prostates measured simultaneously by a needle hydrophone and a PA and ultrasound (US) dual-imaging system, we conducted PASA and correlated the quantified spectral parameter slopes with the cancer grading from histopathology. The PASA results from 18 mice showed significant differences between normal and cancer, and also between low-score cancer and high-score cancer. This study in the clinically relevant TRAMP model of PCa demonstrated that PA imaging and PASA, powered by MB PAA NPs that can label the PCa microarchitectures in vivo after systemic administration, can detect PCa and, more importantly, evaluate cancer aggressiveness.

Recent Advances in Photoacoustic Agents for Theranostic Applications

Photoacoustic agents are widely used in various theranostic applications. By evaluating the biodistribution obtained from photoacoustic images, the effectiveness of theranostic agents in terms of their delivery efficiency and treatment responses can be analyzed. Through this study, we evaluate and summarize the recent advances in photoacoustic-guided phototherapy, particularly in photothermal and photodynamic therapy. This overview can guide the future directions for theranostic development. Because of the recent applications of photoacoustic imaging in clinical trials, theranostic agents with photoacoustic monitoring have the potential to be translated into the clinical world.

Recent Advances in Contrast-Enhanced Photoacoustic Imaging: Overcoming the Physical and Practical Challenges

For decades now, photoacoustic imaging (PAI) has been investigated to realize its potential as a niche biomedical imaging modality. Despite its highly desirable optical contrast and ultrasonic spatiotemporal resolution, PAI is challenged by such physical limitations as a low signal-to-noise ratio (SNR), diminished image contrast due to strong optical attenuation, and a lower-bound on spatial resolution in deep tissue. In addition, contrast-enhanced PAI has faced practical limitations such as insufficient cell-specific targeting due to low delivery efficiency and difficulties in developing clinically translatable agents. Identifying these limitations is essential to the continuing expansion of the field, and substantial advances in developing contrast-enhancing agents, complemented by high-performance image acquisition systems, have synergistically dealt with the challenges of conventional PAI. This review covers the past four years of research on pushing the physical and practical challenges of PAI in terms of SNR/contrast, spatial resolution, targeted delivery, and clinical application. Promising strategies for dealing with each challenge are reviewed in detail, and future research directions for next generation contrast-enhanced PAI are discussed.

The application of indocyanine green in guiding prostate cancer treatment

Objective

Indocyanine green (ICG) with near-infrared fluorescence absorption is approved by the United States Food and Drug Administration for clinical applications in angiography, blood flow evaluation, and liver function assessment. It has strong optical absorption in the near-infrared region, where light can penetrate deepest into biological tissue. We sought to review its value in guiding prostate cancer treatment.

Methods

All related literature at PubMed from January 2000 to December 2020 were reviewed.

Results

Multiple preclinical studies have demonstrated the usefulness of ICG in identifying prostate cancer by using different engineering techniques. Clinical studies have demonstrated the usefulness of ICG in guiding sentinel node dissection during radical prostatectomy, and possible better preservation of neurovascular bundle by identifying landmark prostatic arteries. New techniques such as adding fluorescein in additional to ICG were tested in a limited number of patients with encouraging result. In addition, the use of the ICG was shown to be safe. Even though there are encouraging results, it does not carry sufficient sensitivity and specificity in replacing extended pelvic lymph node dissection during radical prostatectomy.

Conclusion

Multiple preclinical and clinical studies have shown the usefulness of ICG in identifying and guiding treatment for prostate cancer. Larger randomized prospective studies are warranted to further test its usefulness and find new modified approaches.

Ce doped polyaniline nanoparticles for absorption and photoacoustic imaging response to GSH in vitro and in vivo

Glutathione (GSH) is an important biological thiol in cells, which is involved in many physiological processes in the organism and regulates pathological processes of cells. Rapid and accurate monitoring of GSH in vitro and in vivo is quite needed in investigating important biochemical events. In this contribution, innovative cerium (Ce) doped polyaniline (Ce–Fe@PANI NPs) were prepared via Fe(III) induced oxidization polymerization method. Upon addition of GSH, the absorption of Ce–Fe@PANI NPs red shifted from the visible to the NIR region, confirming the excellent absorption response to GSH. Moreover, Ce–Fe@PANI NPs exhibited excellent photoacoustic (PA) imaging enhancement in tube and shifted the PA intensity peak from 680 nm to 820 nm upon addition of GSH. In vitro and in vivo experiment verified that Ce–Fe@PANI NPs can monitor GSH in deep tissues via PA imaging technology. Collectively, this research provides Ce–Fe@PANI NPs would serve as a powerful nanoplatform to realize PA imaging detection of GSH in vitro and in vivo.

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Ce doped polyaniline nanoparticles (Ce–Fe@PANI NPs) with NIR absorption were prepared.

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Ce–Fe@PANI NPs demonstrated absorption response to GSH.

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Ce–Fe@PANI NPs had excellent PA enhancement and shifted the PA intensity peak from 680 nm to 820 nm upon addition of GSH.

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Ce–Fe@PANI NPs can monitor GSH in deep tissues via PA imaging technology in vivo.

Clinical photoacoustic/ultrasound dual-modal imaging: Current status and future trends

Photoacoustic tomography (PAT) is an emerging biomedical imaging modality that combines optical and ultrasonic imaging, providing overlapping fields of view. This hybrid approach allows for a natural integration of PAT and ultrasound (US) imaging in a single platform. Due to the similarities in signal acquisition and processing, the combination of PAT and US imaging creates a new hybrid imaging for novel clinical applications. Over the recent years, particular attention is paid to the development of PAT/US dual-modal systems highlighting mutual benefits in clinical cases, with an aim of substantially improving the specificity and sensitivity for diagnosis of diseases. The demonstrated feasibility and accuracy in these efforts open an avenue of translating PAT/US imaging to practical clinical applications. In this review, the current PAT/US dual-modal imaging systems are discussed in detail, and their promising clinical applications are presented and compared systematically. Finally, this review describes the potential impacts of these combined systems in the coming future.

Higher-order correlation based real-time beamforming in photoacoustic imaging

Although a delay-and-sum (DAS) beamformer is best suited for real-time photoacoustic (PA) image formation, the reconstructed images are often afflicted by noises, sidelobes, and other intense artifacts due to inaccurate assumptions in PA signal correlation. The present work aims to develop a reconstruction method that reduces the occurrence of sidelobes and artifacts and thus improves the reconstructed image quality or imaging performance. This beamformer is fundamentally based on higher-order signal correlation wherein a higher number of delayed PA signals-compared to conventional delay-multiply-and-sum (DMAS)-are combined and summed up. The proposed technique provides significant improvements in resolution, contrast, and signal-to-noise ratio (SNR) compared to traditional beamformers. For real-time implementation, the proposed algorithms were simplified, and their computational complexities were shrunk to the order of DAS [O(N)]. A GPU based study was also performed to validate the real-time capability of the proposed beamformers. For validation studies, both numerical simulation and experiments were conducted. Quantitative evaluation studies involving SNR, contrast ratio, generalized contrast-to-noise ratio, and FWHM demonstrate that the proposed higher-order DMAS beamformer is superior in PA image reconstruction. Conclusively, the proposed beamformer uniquely facilitates real-time PA image reconstruction with an achievable frame rate close to DAS and DMAS but with better imaging performance, which holds promise for real-time PA imaging and its clinical applications.

Contrast Agents for Photoacoustic Imaging: A Review Focusing on the Wavelength Range

Photoacoustic imaging using endogenous chromophores as a contrast has been widely applied in biomedical studies owing to its functional imaging capability at the molecular level. Various exogenous contrast agents have also been investigated for use in contrast-enhanced imaging and functional analyses. This review focuses on contrast agents, particularly in the wavelength range, for use in photoacoustic imaging. The basic principles of photoacoustic imaging regarding light absorption and acoustic release are introduced, and the optical characteristics of tissues are summarized according to the wavelength region. Various types of contrast agents, including organic dyes, semiconducting polymeric nanoparticles, gold nanoparticles, and other inorganic nanoparticles, are explored in terms of their light absorption range in the near-infrared region. An overview of the contrast-enhancing capacity and other functional characteristics of each agent is provided to help researchers gain insights into the development of contrast agents in photoacoustic imaging.

Approaching closed spherical, full-view detection for photoacoustic tomography

SIGNIFICANCE

Photoacoustic tomography (PAT) is a widely explored imaging modality and has excellent potential for clinical applications. On the acoustic detection side, limited-view angle and limited-bandwidth are common key issues in PAT systems that result in unwanted artifacts. While analytical and simulation studies of limited-view artifacts are fairly extensive, experimental setups capable of comparing limited-view to an ideal full-view case are lacking.

AIMS

A custom ring-shaped detector array was assembled and mounted to a 6-axis robot, then rotated and translated to achieve up to 3.8π steradian view angle coverage of an imaged object.

APPROACH

Minimization of negativity artifacts and phantom imaging were used to optimize the system, followed by demonstrative imaging of a star contrast phantom, a synthetic breast tumor specimen phantom, and a vascular phantom.

RESULTS

Optimization of the angular/rotation scans found ≈212 effective detectors were needed for high-quality images, while 15-mm steps were used to increase the field of view as required depending on the size of the imaged object. Example phantoms were clearly imaged with all discerning features visible and minimal artifacts.

CONCLUSIONS

A near full-view closed spherical system has been developed, paving the way for future work demonstrating experimentally the significant advantages of using a full-view PAT setup.

Tapered catheter-based transurethral photoacoustic and ultrasonic endoscopy of the urinary system

Early diagnosis is critical for treating bladder cancer, as this cancer is very aggressive and lethal if detected too late. To address this important clinical issue, a photoacoustic tomography (PAT)-based transabdominal imaging approach was suggested in previous reports, in which its in vivo feasibility was also demonstrated based on a small animal model. However, successful translation of this approach to real clinical settings would be challenging because the human bladder is located at a depth that far exceeds the typical penetration depth of PAT (∼3 cm for in vivo cases). In this study, we developed a tapered catheter-based, transurethral photoacoustic and ultrasonic endoscopic probe with a 2.8 mm outer diameter to investigate whether the well-known benefits of PAT can be harnessed to resolve unmet urological issues, including early diagnosis of bladder cancer. To demonstrate the in vivo imaging capability of the proposed imaging probe, we performed a rabbit model-based urinary system imaging experiment and acquired a 3D microvasculature map distributed in the wall of the urinary system, which is a first in PAT, to the best of our knowledge. We believe that the results strongly support the use of this transurethral imaging approach as a feasible strategy for addressing urological diagnosis issues.

Whole-Body Photoacoustic Imaging Techniques for Preclinical Small Animal Studies

Photoacoustic imaging is a hybrid imaging technique that has received considerable attention in biomedical studies. In contrast to pure optical imaging techniques, photoacoustic imaging enables the visualization of optical absorption properties at deeper imaging depths. In preclinical small animal studies, photoacoustic imaging is widely used to visualize biodistribution at the molecular level. Monitoring the whole-body distribution of chromophores in small animals is a key method used in preclinical research, including drug-delivery monitoring, treatment assessment, contrast-enhanced tumor imaging, and gastrointestinal tracking. In this review, photoacoustic systems for the whole-body imaging of small animals are explored and summarized. The configurations of the systems vary with the scanning methods and geometries of the ultrasound transducers. The future direction of research is also discussed with regard to achieving a deeper imaging depth and faster imaging speed, which are the main factors that an imaging system should realize to broaden its application in biomedical studies.

State of the Art in Carbon Nanomaterials for Photoacoustic Imaging

Photoacoustic imaging using energy conversion from light to ultrasound waves has been developed as a powerful tool to investigate in vivo phenomena due to their complex characteristics. In photoacoustic imaging, endogenous chromophores such as oxygenated hemoglobin, deoxygenated hemoglobin, melanin, and lipid provide useful biomedical information at the molecular level. However, these intrinsic absorbers show strong absorbance only in visible or infrared optical windows and have limited light transmission, making them difficult to apply for clinical translation. Therefore, the development of novel exogenous contrast agents capable of increasing imaging depth while ensuring strong light absorption is required. We report here the application of carbon nanomaterials that exhibit unique physical, mechanical, and electrochemical properties as imaging probes in photoacoustic imaging. Classified into specific structures, carbon nanomaterials are synthesized with different substances according to the imaging purposes to modulate the absorption spectra and highly enhance photoacoustic signals. In addition, functional drugs can be loaded into the carbon nanomaterials composite, and effective in vivo monitoring and photothermal therapy can be performed with cell-specific targeting. Diverse applied cases suggest the high potential of carbon nanomaterial-based photoacoustic imaging in in vivo monitoring for clinical research.

Listening to drug delivery and responses via photoacoustic imaging

Administrating pharmaceutic agents efficiently to achieve the therapeutic effect is the aim of all drug delivery techniques. Recent drug delivery systems aim to deliver high doses of drugs to disease sites accurately while maximizing therapeutic effects and minimizing potential side effects. Key approaches apply image guidance techniques for the quantification of drug biodistribution and pharmacokinetic parameters during drug delivery. This review highlights recent research on image-guided drug delivery systems based on photoacoustic imaging, which has been attracting attention for its non-invasiveness, non-ionizing radiation, and real-time imaging functions. Photoacoustic imaging based on the photothermal conversion efficiency of agents can be easily combined with various phototherapeutics, making them highly suitable for drug delivery therapy platforms. Here, we summarize and compare the characteristics of various types of photoacoustic imaging systems, focus on contrast-enhanced photoacoustic imaging and controlled release of therapeutics in drug delivery systems for synergistic therapies.

Review on Multispectral Photoacoustic Analysis of Cancer: Thyroid and Breast

In recent decades, photoacoustic imaging has been used widely in biomedical research, providing molecular and functional information from biological tissues in vivo. In addition to being used for research in small animals, photoacoustic imaging has also been utilized for in vivo human studies, achieving a multispectral photoacoustic response in deep tissue. There have been several clinical trials for screening cancer patients by analyzing multispectral responses, which in turn provide metabolomic information about the underlying biological tissues. This review summarizes the methods and results of clinical photoacoustic trials available in the literature to date to classify cancerous tissues, specifically of the thyroid and breast. From the review, we can conclude that a great potential exists for photoacoustic imaging to be used as a complementary modality to improve diagnostic accuracy for suspicious tumors, thus significantly benefitting patients’ healthcare.

Photoacoustic imaging systems based on clinical ultrasound platform

Photoacoustic imaging has drawn a significant amount of attention due to its unique capacity for functional, metabolic, and molecular imaging, which is achieved by the combination of optical excitation and acoustic detection. With both strengths of light and ultrasound, photoacoustic images can provide strong optical contrast at high ultrasound resolution in deep tissue. As photoacoustic imaging can be used to visualize complementary information to ultrasound imaging using the same data acquisition process, several studies have been conducted on combining photoacoustic imaging with existing clinical ultrasound systems. This review highlights our development of a photoacoustic/ultrasound dual-modal imaging system, various features and functionalities implemented for clinical translation, and preclinical/clinical studies performed by using the systems.

The emerging role of photoacoustic imaging in clinical oncology

Clinical oncology can benefit substantially from imaging technologies that reveal physiological characteristics with multiscale observations. Complementing conventional imaging modalities, photoacoustic imaging (PAI) offers rapid imaging (for example, cross-sectional imaging in real time or whole-breast scanning in 10-15 s), scalably high levels of spatial resolution, safe operation and adaptable configurations. Most importantly, this novel imaging modality provides informative optical contrast that reveals details on anatomical, functional, molecular and histological features. In this Review, we describe the current state of development of PAI and the emerging roles of this technology in cancer screening, diagnosis and therapy. We comment on the performance of cutting-edge photoacoustic platforms, and discuss their clinical applications and utility in various clinical studies. Notably, the clinical translation of PAI is accelerating in the areas of macroscopic and mesoscopic imaging for patients with breast or skin cancers, as well as in microscopic imaging for histopathology. We also highlight the potential of future developments in technological capabilities and their clinical implications, which we anticipate will lead to PAI becoming a desirable and widely used imaging modality in oncological research and practice.

Estimation of the Prostate Volume from Abdominal Ultrasound Images by Image-Patch Voting

Estimation of the prostate volume with ultrasound offers many advantages such as portability, low cost, harmlessness, and suitability for real-time operation. Abdominal Ultrasound (AUS) is a practical procedure that deserves more attention in automated prostate-volume-estimation studies. As the experts usually consider automatic end-to-end volume-estimation procedures as non-transparent and uninterpretable systems, we proposed an expert-in-the-loop automatic system that follows the classical prostate-volume-estimation procedures. Our system directly estimates the diameter parameters of the standard ellipsoid formula to produce the prostate volume. To obtain the diameters, our system detects four diameter endpoints from the transverse and two diameter endpoints from the sagittal AUS images as defined by the classical procedure. These endpoints are estimated using a new image-patch voting method to address characteristic problems of AUS images. We formed a novel prostate AUS data set from 305 patients with both transverse and sagittal planes. The data set includes MRI images for 75 of these patients. At least one expert manually marked all the data. Extensive experiments performed on this data set showed that the proposed system results ranged among experts’ volume estimations, and our system can be used in clinical practice.

Review on Optical Imaging Techniques for Multispectral Analysis of Nanomaterials

Biomedical imaging is an essential tool for investigating biological responses in vivo. Among the several imaging techniques, optical imaging systems with multispectral analysis of nanoparticles have been widely investigated due to their ability to distinguish the substances in biological tissues in vivo. This review article focus on multispectral optical imaging techniques that can provide molecular functional information. We summarize the basic principle of the spectral unmixing technique that enables the delineation of optical chromophores. Then, we explore the principle, typical system configuration, and biomedical applications of the representative optical imaging techniques, which are fluorescence imaging, two-photon microscopy, and photoacoustic imaging. The results in the recent studies show the great potential of the multispectral analysis techniques for monitoring responses of biological systems in vivo.

BSA-templated Ultrasmall Ag/Gd2O3 as A Self-enabled Nanotheranostics for MR/CT/PA tri-modality Imaging and Photothermal Therapy

It is becoming more and more important to effectively integrate multiple complementary diagnostic imaging and synergistic therapy into a nano-platform, but it is still challenging. Here, we used bovine serum...

Modeling combined ultrasound and photoacoustic imaging: Simulations aiding device development and artificial intelligence

Combined ultrasound and photoacoustic (USPA) imaging has attracted several pre-clinical and clinical applications due to its ability to simultaneously display structural, functional, and molecular information of deep biological tissue in real time. However, the depth and wavelength dependent optical attenuation and the unknown optical and acoustic heterogeneities limit the USPA imaging performance in deep tissue regions. Novel instrumentation, image reconstruction, and artificial intelligence (AI) methods are currently being investigated to overcome these limitations and improve the USPA image quality. Effective implementation of these approaches requires a reliable USPA simulation tool capable of generating US based anatomical and PA based molecular contrasts of deep biological tissue. Here, we developed a hybrid USPA simulation platform by integrating finite element models of light (NIRFast) and ultrasound (k-Wave) propagations for co-simulation of B-mode US and PA images. The platform allows optimization of different design parameters for USPA devices, such as the aperture size and frequency of both light and ultrasound detector arrays. For designing tissue-realistic digital phantoms, a dictionary-based function has been added to k-Wave to generate various levels of ultrasound speckle contrast. The feasibility of modeling US imaging combined with optical fluence dependent multispectral PA imaging is demonstrated using homogeneous as well as heterogeneous tissue phantoms mimicking human organs (e.g., prostate and finger). In addition, we also demonstrate the potential of the simulation platform to generate large scale application-specific training and test datasets for AI enhanced USPA imaging. The complete USPA simulation codes together with the supplementary user guides have been posted to an open-source repository (https://github.com/KothapalliLabPSU/US-PA_simulation_codes).

High-speed photoacoustic microscopy: A review dedicated on light sources

In recent years, many methods have been investigated to improve imaging speed in photoacoustic microscopy (PAM). These methods mainly focused upon three critical factors contributing to fast PAM: laser pulse repetition rate, scanning speed, and computing power of the microprocessors. A high laser repetition rate is fundamentally the most crucial factor to increase the PAM speed. In this paper, we review methods adopted for fast PAM systems in detail, specifically with respect to light sources. To the best of our knowledge, ours is the first review article analyzing the fundamental requirements for developing high-speed PAM and their limitations from the perspective of light sources.

Simultaneous Denoising and Localization Network for Photoacoustic Target Localization

A significant research problem of recent interest is the localization of targets like vessels, surgical needles, and tumors in photoacoustic (PA) images.To achieve accurate localization, a high photoacoustic signal-to-noise ratio (SNR) is required. However, this is not guaranteed for deep targets, as optical scattering causes an exponential decay in optical fluence with respect to tissue depth. To address this, we develop a novel deep learning method designed to explicitly exhibit robustness to noise present in photoacoustic radio-frequency (RF) data. More precisely, we describe and evaluate a deep neural network architecture consisting of a shared encoder and two parallel decoders. One decoder extracts the target coordinates from the input RF data while the other boosts the SNR and estimates clean RF data. The joint optimization of the shared encoder and dual decoders lends significant noise robustness to the features extracted by the encoder, which in turn enables the network to contain detailed information about deep targets that may be obscured by noise. Additional custom layers and newly proposed regularizers in the training loss function (designed based on observed RF data signal and noise behavior) serve to increase the SNR in the cleaned RF output and improve model performance. To account for depth-dependent strong optical scattering, our network was trained with simulated photoacoustic datasets of targets embedded at different depths inside tissue media of different scattering levels. The network trained on this novel dataset accurately locates targets in experimental PA data that is clinically relevant with respect to the localization of vessels, needles, or brachytherapy seeds. We verify the merits of the proposed architecture by outperforming the state of the art on both simulated and experimental datasets.

Superiorized Photo-Acoustic Non-NEgative Reconstruction (SPANNER) for Clinical Photoacoustic Imaging

Photoacoustic (PA) imaging can revolutionize medical ultrasound by augmenting it with molecular information. However, clinical translation of PA imaging remains a challenge due to the limited viewing angles and imaging depth. Described here is a new robust algorithm called Superiorized Photo-Acoustic Non-NEgative Reconstruction (SPANNER), designed to reconstruct PA images in real-time and to address the artifacts associated with limited viewing angles and imaging depth. The method utilizes precise forward modeling of the PA propagation and reception of signals while accounting for the effects of acoustic absorption, element size, shape, and sensitivity, as well as the transducer's impulse response and directivity pattern. A fast superiorized conjugate gradient algorithm is used for inversion. SPANNER is compared to three reconstruction algorithms: delay-and-sum (DAS), universal back-projection (UBP), and model-based reconstruction (MBR). All four algorithms are applied to both simulations and experimental data acquired from tissue-mimicking phantoms, ex vivo tissue samples, and in vivo imaging of the prostates in patients. Simulations and phantom experiments highlight the ability of SPANNER to improve contrast to background ratio by up to 20 dB compared to all other algorithms, as well as a 3-fold increase in axial resolution compared to DAS and UBP. Applying SPANNER on contrast-enhanced PA images acquired from prostate cancer patients yielded a statistically significant difference before and after contrast agent administration, while the other three image reconstruction methods did not, thus highlighting SPANNER's performance in differentiating intrinsic from extrinsic PA signals and its ability to quantify PA signals from the contrast agent more accurately.

Progress in micro/nano sensors and nanoenergy for future AIoT-based smart home applications

Self-sustainable sensing systems composed of micro/nano sensors and nano-energy harvesters contribute significantly to developing the internet of things (IoT) systems. As one of the most promising IoT applications, smart home relies on implementing wireless sensor networks with miniaturized and multi-functional sensors, and distributed, reliable, and sustainable power sources, namely energy harvesters with a variety of conversion mechanisms. To extend the capabilities of IoT in the smart home, a technology fusion of IoT and artificial intelligence (AI), called the artificial intelligence of things (AIoT), enables the detection, analysis, and decision-making functions with the aids of machine learning assisted algorithms to form a smart home based intelligent system. In this review, we introduce the conventional rigid microelectromechanical system (MEMS) based micro/nano sensors and energy harvesters, followed by presenting the advances in the wearable counterparts for better human interactions. We then discuss the viable integration approaches for micro/nano sensors and energy harvesters to form self-sustainable IoT systems. Whereafter, we emphasize the recent development of AIoT based systems and the corresponding applications enabled by the machine learning algorithms. Smart home based healthcare technology enabled by the integrated multi-functional sensing platform and bioelectronic medicine is also presented as an important future direction, as well as wearable photonics sensing system as a complement to the wearable electronics sensing system.

Photoacoustic-guided surgery from head to toe [Invited]

Photoacoustic imaging-the combination of optics and acoustics to visualize differences in optical absorption - has recently demonstrated strong viability as a promising method to provide critical guidance of multiple surgeries and procedures. Benefits include its potential to assist with tumor resection, identify hemorrhaged and ablated tissue, visualize metal implants (e.g., needle tips, tool tips, brachytherapy seeds), track catheter tips, and avoid accidental injury to critical subsurface anatomy (e.g., major vessels and nerves hidden by tissue during surgery). These benefits are significant because they reduce surgical error, associated surgery-related complications (e.g., cancer recurrence, paralysis, excessive bleeding), and accidental patient death in the operating room. This invited review covers multiple aspects of the use of photoacoustic imaging to guide both surgical and related non-surgical interventions. Applicable organ systems span structures within the head to contents of the toes, with an eye toward surgical and interventional translation for the benefit of patients and for use in operating rooms and interventional suites worldwide. We additionally include a critical discussion of complete systems and tools needed to maximize the success of surgical and interventional applications of photoacoustic-based technology, spanning light delivery, acoustic detection, and robotic methods. Multiple enabling hardware and software integration components are also discussed, concluding with a summary and future outlook based on the current state of technological developments, recent achievements, and possible new directions.

A tumor microenvironment-induced absorption red-shifted polymer nanoparticle for simultaneously activated photoacoustic imaging and photothermal therapy

Tumor microenvironment-responsive therapy has enormous application potential in the diagnosis and treatment of cancer. The glutathione (GSH) level has been shown to be significantly increased in tumor tissues. Thus, GSH can be used as an effective endogenous molecule for diagnosis and tumor microenvironment-activated therapy. In this study, we prepared a tumor microenvironment-induced, absorption spectrum red-shifted, iron-copper co-doped polyaniline nanoparticle (Fe-Cu@PANI). The Cu(II) in this nanoparticle can undergo a redox reaction with GSH in tumors. The redox reaction induces a red shift in the absorption spectrum of the Fe-Cu@PANI nanoparticles from the visible to the near-infrared region accompanying with the etching of this nanoparticle, which simultaneously activates tumor photoacoustic imaging and photothermal therapy, thereby improving the accuracy of in vivo tumor imaging and the efficiency of photothermal therapy. The nanoparticle prepared in this study has broad application prospects in the diagnosis and treatment of cancer.

Transrectal Ultrasound and Photoacoustic Imaging Probe for Diagnosis of Prostate Cancer

A combined transrectal ultrasound and photoacoustic (TRUS-PA) imaging probe was developed for the clear visualization of morphological changes and microvasculature distribution in the prostate, as this is required for accurate diagnosis and biopsy. The probe consisted of a miniaturized 128-element 7 MHz convex array transducer with 134.5° field-of-view (FOV), a bifurcated optical fiber bundle, and two optical lenses. The design goal was to make the size of the TRUS-PA probe similar to that of general TRUS probes (i.e., about 20 mm), for the convenience of the patients. New flexible printed circuit board (FPCB), acoustic structure, and optical lens were developed to meet the requirement of the probe size, as well as to realize a high-performance TRUS-PA probe. In visual assessment, the PA signals obtained with the optical lens were 2.98 times higher than those without the lens. Moreover, the in vivo experiment with the xenograft BALB/c (Albino, Immunodeficient Inbred Strain) mouse model showed that TRUS-PA probe was able to acquire the entire PA image of the mouse tight behind the porcine intestine about 25 mm depth. From the ex vivo and in vivo experimental results, it can be concluded that the developed TRUS-PA probe is capable of improving PA image quality, even though the TRUS-PA probe has a cross-section size and an FOV comparable to those of general TRUS probes.

A multimodal molecular imaging approach targeting urokinase plasminogen activator receptor for the diagnosis, resection and surveillance of urothelial cell carcinoma

With a 5-year recurrence rate of 30-78%, urothelial cell carcinoma (UCC) rates amongst the highest of all solid malignancies. Consequently, after transurethral resection, patients are subjugated to life-long endoscopic surveillance. A multimodal near-infrared (NIR) fluorescence-based imaging strategy can improve diagnosis, resection and surveillance, hence increasing quality of life.

METHODS

Expression of urokinase plasminogen activator receptor (uPAR) and epithelial cell adhesion molecule (EpCAM) are determined on paraffin-embedded human UCC using immunohistochemistry and on UCC cell lines by flow cytometry. MNPR-101, a humanised monoclonal antibody targeting uPAR is conjugated to IRDye800CW and binding is validated in vitro using surface plasmon resonance and cell-based binding assays. In vivo NIR fluorescence and photoacoustic three-dimensional (3D) imaging are performed with subcutaneously growing human UM-UC-3luc2 cells in BALB/c-nude mice. The translational potential is confirmed in a metastasising UM-UC-3luc2 orthotopic mouse model. Infliximab-IRDye800CW and rituximab-IRDye800CW are used as controls.

RESULTS

UCCs show prominent uPAR expression at the tumour-stroma interface and EpCAM on epithelial cells. uPAR and EpCAM are expressed by 6/7 and 4/7 UCC cell lines, respectively. In vitro, MNPR-101-IRDye800CW has a picomolar affinity for domain 2-3 of uPAR. In vivo fluorescence imaging with MNPR-101-IRDye800CW, specifically delineates both subcutaneous and orthotopic tumours with tumour-to-background ratios reaching as high as 6.8, differing significantly from controls (p < 0.0001). Photoacoustic 3D in depth imaging confirms the homogenous distribution of MNPR-101-IRDye800CW through the tumour.

CONCLUSIONS

MNPR-101-IRDye800CW is suitable for multimodal imaging of UCC, awaiting clinical translation.

Simultaneous Dual-Modal Multispectral Photoacoustic and Ultrasound Macroscopy for Three-Dimensional Whole-Body Imaging of Small Animals

Photoacoustic imaging is a promising medical imaging technique that provides excellent function imaging of an underlying biological tissue or organ. However, it is limited in providing structural information compared to other imaging modalities, such as ultrasound imaging. Thus, to offer complete morphological details of biological tissues, photoacoustic imaging is typically integrated with ultrasound imaging. This dual-modal imaging technique is already implemented on commercial clinical ultrasound imaging platforms. However, commercial platforms suffer from limited elevation resolution compared to the lateral and axial resolution. We have successfully developed a dual-modal photoacoustic and ultrasound imaging to address these limitations, specifically targeting animal studies. The system can acquire whole-body images of mice in vivo and provide complementary structural and functional information of biological tissue information simultaneously. The color-coded depth information can be readily obtained in photoacoustic images using complementary information from ultrasound images. The system can be used for several biomedical applications, including drug delivery, biodistribution assessment, and agent testing.

Photoacoustic Imaging of Human Vasculature Using LED versus Laser Illumination: A Comparison Study on Tissue Phantoms and In Vivo Humans

Vascular diseases are becoming an epidemic with an increasing aging population and increases in obesity and type II diabetes. Point-of-care (POC) diagnosis and monitoring of vascular diseases is an unmet medical need. Photoacoustic imaging (PAI) provides label-free multiparametric information of deep vasculature based on strong absorption of light photons by hemoglobin molecules. However, conventional PAI systems use bulky nanosecond lasers which hinders POC applications. Recently, light-emitting diodes (LEDs) have emerged as cost-effective and portable optical sources for the PAI of living subjects. However, state-of-art LED arrays carry significantly lower optical energy (<0.5 mJ/pulse) and high pulse repetition frequencies (PRFs) (4 KHz) compared to the high-power laser sources (100 mJ/pulse) with low PRFs of 10 Hz. Given these tradeoffs between portability, cost, optical energy and frame rate, this work systematically studies the deep tissue PAI performance of LED and laser illuminations to help select a suitable source for a given biomedical application. To draw a fair comparison, we developed a fiberoptic array that delivers laser illumination similar to the LED array and uses the same ultrasound transducer and data acquisition platform for PAI with these two illuminations. Several controlled studies on tissue phantoms demonstrated that portable LED arrays with high frame averaging show higher signal-to-noise ratios (SNRs) of up to 30 mm depth, and the high-energy laser source was found to be more effective for imaging depths greater than 30 mm at similar frame rates. Label-free in vivo imaging of human hand vasculature studies further confirmed that the vascular contrast from LED-PAI is similar to laser-PAI for up to 2 cm depths. Therefore, LED-PAI systems have strong potential to be a mobile health care technology for diagnosing vascular diseases such as peripheral arterial disease and stroke in POC and resource poor settings.