Combined multi-modal photoacoustic tomography, optical coherence tomography (OCT) and OCT angiography system with an articulated probe for in vivo human skin structure and vasculature imaging

Advanced nanomaterials for imaging of eye diseases

Background and purpose

Vision impairment and blindness present significant global challenges, with common causes including age-related macular degeneration, diabetes, retinitis pigmentosa, and glaucoma. Advanced imaging tools, such as optical coherence tomography, fundus photography, photoacoustic microscopy, and fluorescence imaging, play a crucial role in improving therapeutic interventions and diagnostic methods. Contrast agents are often employed with these tools to enhance image clarity and signal detection. This review aims to explore the commonly used contrast agents in ocular disease imaging.

Experimental approach

The first section of the review delves into advanced ophthalmic imaging techniques, outlining their importance in addressing vision-related issues. The emphasis is on the efficacy of therapeutic interventions and diagnostic methods, establishing a foundation for the subsequent exploration of contrast agents.

Key results

This review focuses on the role of contrast agents, with a specific emphasis on gold nanoparticles, particularly gold nanorods. The discussion highlights how these contrast agents optimize imaging in ocular disease diagnosis and monitoring, emphasizing their unique properties that enhance signal detection and imaging precision.

Conclusion

The final section, we explores both organic and inorganic contrast agents and their applications in specific conditions such as choroidal neovascularization, retinal neovascularization, and stem cell tracking. The review concludes by addressing the limitations of current contrast agent usage and discussing potential future clinical applications. This comprehensive exploration contributes to advancing our understanding of contrast agents in ocular disease imaging and sets the stage for further research and development in the field.

The LMIT: Light-mediated minimally-invasive theranostics in oncology

Minimally-invasive diagnosis and therapy have gradually become the trend and research hotspot of current medical applications. The integration of intraoperative diagnosis and treatment is a development important direction for real-time detection, minimally-invasive diagnosis and therapy to reduce mortality and improve the quality of life of patients, so called minimally-invasive theranostics (MIT). Light is an important theranostic tool for the treatment of cancerous tissues. Light-mediated minimally-invasive theranostics (LMIT) is a novel evolutionary technology that integrates diagnosis and therapeutics for the less invasive treatment of diseased tissues. Intelligent theranostics would promote precision surgery based on the optical characterization of cancerous tissues. Furthermore, MIT also requires the assistance of smart medical devices or robots. And, optical multimodality lay a solid foundation for intelligent MIT. In this review, we summarize the important state-of-the-arts of optical MIT or LMIT in oncology. Multimodal optical image-guided intelligent treatment is another focus. Intraoperative imaging and real-time analysis-guided optical treatment are also systemically discussed. Finally, the potential challenges and future perspectives of intelligent optical MIT are discussed.

Visualization of Subcutaneous Blood Vessels Based on Hyperspectral Imaging and Three-Wavelength Index Images

Blood vessel visualization technology allows nursing staff to transition from traditional palpation or touch to locate the subcutaneous blood vessels to visualized localization by providing a clear visual aid for performing various medical procedures accurately and efficiently involving blood vessels; this can further improve the first-attempt puncture success rate for nursing staff and reduce the pain of patients. We propose a novel technique for hyperspectral visualization of blood vessels in human skin. An experiment with six participants with different skin types, race, and nationality backgrounds is described. A mere separation of spectral layers for different skin types is shown to be insufficient. The use of three-wavelength indices in imaging has shown a significant improvement in the quality of results compared to using only two-wavelength indices. This improvement can be attributed to an increase in the contrast ratio, which can be as high as 25%. We propose and implement a technique for finding new index formulae based on an exhaustive search and a binary blood-vessel image obtained through an expert assessment. As a result of the search, a novel index formula was deduced, allowing high-contrast blood vessel images to be generated for any skin type.

In vivo microscopy as an adjunctive tool to guide detection, diagnosis, and treatment

SIGNIFICANCE

There have been numerous academic and commercial efforts to develop high-resolution in vivo microscopes for a variety of clinical use cases, including early disease detection and surgical guidance. While many high-profile studies, commercialized products, and publications have resulted from these efforts, mainstream clinical adoption has been relatively slow other than for a few clinical applications (e.g., dermatology).

AIM

Here, our goals are threefold: (1) to introduce and motivate the need for in vivo microscopy (IVM) as an adjunctive tool for clinical detection, diagnosis, and treatment, (2) to discuss the key translational challenges facing the field, and (3) to propose best practices and recommendations to facilitate clinical adoption.

APPROACH

We will provide concrete examples from various clinical domains, such as dermatology, oral/gastrointestinal oncology, and neurosurgery, to reinforce our observations and recommendations.

RESULTS

While the incremental improvement and optimization of IVM technologies should and will continue to occur, future translational efforts would benefit from the following: (1) integrating clinical and industry partners upfront to define and maintain a compelling value proposition, (2) identifying multimodal/multiscale imaging workflows, which are necessary for success in most clinical scenarios, and (3) developing effective artificial intelligence tools for clinical decision support, tempered by a realization that complete adoption of such tools will be slow.

CONCLUSIONS

The convergence of imaging modalities, academic-industry-clinician partnerships, and new computational capabilities has the potential to catalyze rapid progress and adoption of IVM in the next few decades.

Fully Customized Photoacoustic System Using Doubly Q-Switched Nd:YAG Laser and Multiple Axes Stages for Laboratory Applications

We developed a customized doubly Q-switched laser that can control the pulse width to easily find weak acoustic signals for photoacoustic (PA) systems. As the laser was constructed using an acousto-optic Q-switcher, in contrast to the existing commercial laser system, it is easier to control the pulse repetition rate and pulse width. The laser has the following control ranges: 10 Hz–10 kHz for the pulse repetition rate, 40–150 ns for the pulse width, and 50–500 μJ for the pulse energy. Additionally, a custom-made modularized sample stage was used to develop a fully customized PA system. The modularized sample stage has a nine-axis control unit design for the PA system, allowing the sample target and transducer to be freely adjusted. This makes the system suitable for capturing weak PA signals. Images were acquired and processed for widely used sample targets (hair and insulating tape) with the developed fully customized PA system. The customized doubly Q-switched laser-based PA imaging system presented in this paper can be modified for diverse conditions, including the wavelength, frequency, pulse width, and sample target; therefore, we expect that the proposed technique will be helpful in conducting fundamental and applied research for PA imaging system applications.

In Vivo Identification of Skin Photodamage Induced by Fractional CO2 and Picosecond Nd:YAG Lasers with Optical Coherence Tomography

Fractional laser treatment is commonly used for dermatological applications, enabling effective induction of collagen regeneration and significantly reducing recovery time. However, it is challenging to observe laser-induced photodamage beneath the tissue surface in vivo, making the non-invasive evaluation of treatment outcomes difficult. For in vivo real-time study of the photodamage induced by fractional pulsed CO₂ and Nd:YAG lasers commonly utilized for clinical therapy, a portable spectral-domain optical coherence tomography (SD-OCT) system was implemented for clinical studies. The photodamage caused by two lasers, including photothermal and photoacoustic effects, was investigated using OCT, together with the correlation between photodamage and exposure energy. Additionally, to investigate the change in the optical properties of tissue due to photodamage, the attenuation coefficients and damaged areas of normal skin and laser-treated skin were estimated for comparison. Finally, the recovery of the exposed skin with both lasers was also compared using OCT. The results show that OCT can be a potential solution for in vivo investigation of laser-induced tissue damage and quantitative evaluation.

An Excitation-Reception Collinear Probe for Ultrasonic, Photoacoustic, and Thermoacoustic Tri-Modal Volumetric Imaging

Imaging systems that integrate multiple modalities can reveal complementary anatomic and functional information as they exploit different contrast mechanisms, which have shown great application potential and advantages in preclinical studies. A portable and easy-to-use imaging probe will be more conducive to transfer to clinical practice. Here, we present a tri-modal ultrasonic (US), photoacoustic (PA), and thermoacoustic (TA) imaging system with an excitation-reception collinear probe. The acoustic field, light field, and electric field of the probe were designed to be coaxial, realizing homogeneous illumination and high-sensitivity detection at the same detection position. US images can provide detailed information about structures, PA images can delineate the morphology of blood vessels in tissues, and TA images can reveal dielectric properties of the tissues. Moreover, phantoms and in vivo human finger experiments were performed by the tri-modal imaging system to demonstrate its performance. The results show that the tri-modal imaging system with the proposed probe has the ability to detect small breast tumors with a radius of only 2.5 mm and visualize the anatomical structure of the finger in three dimensions. Our work confirms that the tri-modal imaging system equipped with a collinear probe can be applied to a variety of different scenarios, which lays a solid foundation for the application of the tri-modality system in clinical trials.

Enhanced medical diagnosis for dOCTors: a perspective of optical coherence tomography

SIGNIFICANCE

After three decades, more than 75,000 publications, tens of companies being involved in its commercialization, and a global market perspective of about USD 1.5 billion in 2023, optical coherence tomography (OCT) has become one of the fastest successfully translated imaging techniques with substantial clinical and economic impacts and acceptance.

AIM

Our perspective focuses on disruptive forward-looking innovations and key technologies to further boost OCT performance and therefore enable significantly enhanced medical diagnosis.

APPROACH

A comprehensive review of state-of-the-art accomplishments in OCT has been performed.

RESULTS

The most disruptive future OCT innovations include imaging resolution and speed (single-beam raster scanning versus parallelization) improvement, new implementations for dual modality or even multimodality systems, and using endogenous or exogenous contrast in these hybrid OCT systems targeting molecular and metabolic imaging. Aside from OCT angiography, no other functional or contrast enhancing OCT extension has accomplished comparable clinical and commercial impacts. Some more recently developed extensions, e.g., optical coherence elastography, dynamic contrast OCT, optoretinography, and artificial intelligence enhanced OCT are also considered with high potential for the future. In addition, OCT miniaturization for portable, compact, handheld, and/or cost-effective capsule-based OCT applications, home-OCT, and self-OCT systems based on micro-optic assemblies or photonic integrated circuits will revolutionize new applications and availability in the near future. Finally, clinical translation of OCT including medical device regulatory challenges will continue to be absolutely essential.

CONCLUSIONS

With its exquisite non-invasive, micrometer resolution depth sectioning capability, OCT has especially revolutionized ophthalmic diagnosis and hence is the fastest adopted imaging technology in the history of ophthalmology. Nonetheless, OCT has not been completely exploited and has substantial growth potential-in academics as well as in industry. This applies not only to the ophthalmic application field, but also especially to the original motivation of OCT to enable optical biopsy, i.e., the in situ imaging of tissue microstructure with a resolution approaching that of histology but without the need for tissue excision.

Progress of clinical translation of handheld and semi-handheld photoacoustic imaging

Photoacoustic imaging (PAI), featuring rich contrast, high spatial/temporal resolution and deep penetration, is one of the fastest-growing biomedical imaging technology over the last decade. To date, numbers of handheld and semi-handheld photoacoustic imaging devices have been reported with corresponding potential clinical applications. Here, we summarize emerged handheld and semi-handheld systems in terms of photoacoustic computed tomography (PACT), optoacoustic mesoscopy (OAMes), and photoacoustic microscopy (PAM). We will discuss each modality in three aspects: laser delivery, scanning protocol, and acoustic detection. Besides new technical developments, we also review the associated clinical studies, and the advantages/disadvantages of these new techniques. In the end, we propose the challenges and perspectives of miniaturized PAI in the future.

Optoacoustic imaging of the skin

Optoacoustic (OA, photoacoustic) imaging capitalizes on the synergistic combination of light excitation and ultrasound detection to empower biological and clinical investigations with rich optical contrast while effectively bridging the gap between micro and macroscopic imaging realms. State-of-the-art OA embodiments consistently provide images at micron-scale resolution through superficial tissue layers by means of focused illumination that can be smoothly exchanged for acoustic-resolution images at diffuse light depths of several millimetres to centimetres via ultrasound beamforming or tomographic reconstruction. Taken together, this unique multi-scale imaging capacity opens unprecedented capabilities for high-resolution in vivo interrogations of the skin at scalable depths. Moreover, diverse anatomical and functional information is retrieved via dynamic mapping of endogenous chromophores such as haemoglobin, melanin, lipids, collagen, water and others. This, along with the use of non-ionizing radiation, facilitates a clinical translation of the OA modalities. We review recent progress in OA imaging of the skin in preclinical and clinical studies exploiting the rich contrast provided by endogenous substances in tissues. The imaging capabilities of existing approaches are discussed in the context of initial translational studies on skin cancer, inflammatory skin diseases, wounds and other conditions.

Quadruple ultrasound, photoacoustic, optical coherence, and fluorescence fusion imaging with a transparent ultrasound transducer

Ultrasound and optical imagers are used widely in a variety of biological and medical applications. In particular, multimodal implementations combining light and sound have been actively investigated to improve imaging quality. However, the integration of optical sensors with opaque ultrasound transducers suffers from low signal-to-noise ratios, high complexity, and bulky form factors, significantly limiting its applications. Here, we demonstrate a quadruple fusion imaging system using a spherically focused transparent ultrasound transducer that enables seamless integration of ultrasound imaging with photoacoustic imaging, optical coherence tomography, and fluorescence imaging. As a first application, we comprehensively monitored multiparametric responses to chemical and suture injuries in rats' eyes in vivo, such as corneal neovascularization, structural changes, cataracts, and inflammation. As a second application, we successfully performed multimodal imaging of tumors in vivo, visualizing melanomas without using labels and visualizing 4T1 mammary carcinomas using PEGylated gold nanorods. We strongly believe that the seamlessly integrated multimodal system can be used not only in ophthalmology and oncology but also in other healthcare applications with broad impact and interest.

Optical Coherence Tomography Angiography Monitors Cutaneous Wound Healing under Angiogenesis-Promoting Treatment in Diabetic and Non-Diabetic Mice

During wound healing, the rapid re-establishment of a functional microcirculation in the wounded tissue is of utmost importance. We applied optical coherence tomography (OCT) angiography to evaluate vascular remodeling in an excisional wound model in the pinnae of C57BL/6 and db/db mice receiving different proangiogenic topical treatments. Analysis of the high-resolution OCT angiograms, including the four quantitative parameters vessel density, vessel length, number of bifurcations, and vessel tortuosity, revealed changes of the microvasculature and allowed identification of the overlapping wound healing phases hemostasis, inflammation, proliferation, and remodeling. Angiograms acquired in the inflammatory phase in the first days showed a dilation of vessels and recruitment of pre-existing capillaries. In the proliferative phase, angiogenesis with the sprouting of new capillaries into the wound tissue led to an increase of the OCT angiography parameters vessel density, normalized vessel length, number of bifurcations, and vessel tortuosity by 28–47%, 39–52%, 33–48%, and 3–8% versus baseline, respectively. After the peak observed on study days four to seven, the parameters slowly decreased but remained still elevated 18 days after wounding, indicating a continuing remodeling phase. Our study suggests that OCT angiography has the potential to serve as a valuable preclinical research tool in studies investigating impaired vascular remodeling during wound healing and potential new treatment strategies.

Photoacoustic Imaging

Photoacoustic imaging (PAI) is an emerging imaging modality that shows great potential for preclinical research and clinical practice. As a hybrid technique, PAI uniquely combines the advantages of optical excitation and of acoustic detection. Optical excitation provides a rich contrast mechanism from either endogenous or exogenous chromophores, allowing PAI to perform biochemical, functional, and molecular imaging. Acoustic detection benefits from the low scattering of ultrasound in biological tissue, enabling PAI to generate high-resolution images in both the optical ballistic and diffusive regimes. Accordingly, this hybrid imaging modality features high sensitivity to optical absorption and wide scalability of spatial resolution with the desired imaging depth. Over the past two decades, the photoacoustic technique has led to a variety of exciting discoveries and applications from laboratory research to clinical patient care. In biological research, PAI has become an irreplaceable tool, providing functional optical contrast with high spatiotemporal resolution. Translational PAI also attracted growing interest in clinical applications including tumor margin examination, internal organ imaging, breast cancer screening, and sentinel lymph node mapping, among others.

Imaging Motion: A Comprehensive Review of Optical Coherence Tomography Angiography

Optical coherence tomography (OCT) is a three-dimensional (3-D) optical imaging technology that provides noninvasive, micrometer resolution images of structural interiors within biological samples with an approximately 1 ~ 2 mm penetration depth. Over the last decades, advances in OCT have revolutionized biomedical imaging by demonstrating a potential of optical biopsy in preclinical and clinical settings. Recently, functional OCT imaging has shown a promise as angiography to visualize cell-perfused vasculatures in the tissue bed in vivo without requiring any exogenous contrast agents. This new technology termed OCT angiography (OCTA) possesses a unique imaging capability of delineating tissue morphology and blood or lymphatic vessels down to capillaries at real-time acquisition rates. For the past 10 years since 2007, OCTA has been proven to be a useful tool to identify disorder or dysfunction in tissue microcirculation from both experimental animal studies and clinical studies in ophthalmology and dermatology. In this section, we overview about OCTA including a basic principle of OCTA explained with simple optical physics, and its scan protocols and post-processing algorithms for acquisition of angiography. Then, potential and challenge of OCTA for clinical settings are shown with outcomes of human studies.

Towards non-contact photoacoustic imaging [review]

Photoacoustic imaging (PAI) takes advantage of both optical and ultrasound imaging properties to visualize optical absorption with high resolution and contrast. Photoacoustic microscopy (PAM) is usually categorized with all-optical microscopy techniques such as optical coherence tomography or confocal microscopes. Despite offering high sensitivity, novel imaging contrast, and high resolution, PAM is not generally an all-optical imaging method unlike the other microscopy techniques. One of the significant limitations of photoacoustic microscopes arises from their need to be in physical contact with the sample through a coupling media. This physical contact, coupling, or immersion of the sample is undesirable or impractical for many clinical and pre-clinical applications. This also limits the flexibility of photoacoustic techniques to be integrated with other all-optical imaging microscopes for providing complementary imaging contrast. To overcome these limitations, several non-contact photoacoustic signal detection approaches have been proposed. This paper presents a brief overview of current non-contact photoacoustic detection techniques with an emphasis on all-optical detection methods and their associated physical mechanisms.

Cutaneous optical coherence tomography for longitudinal volumetric assessment of intradermal volumes in a mouse model

Clinical evaluation of skin lesions requires precise and reproducible technologies for their qualitative and quantitative assessment. In this study, we investigate the applicability of a custom-built dermatologic OCT system for longitudinal assessment of intradermal volumes in a mouse model. The OCT, based on an akinetic swept laser working at 1310 nm was employed for visualization and quantification of intradermal deposits of three different hyaluronic acid-based hydrogel formulations - one commercial and two test substances. Hydrogels were applied in 22 BALB/c mice, and measurements were performed over a six-month time period. All hydrogels increased in volume within the first weeks and degraded steadily thereafter. The half-lifes of the test hydrogels (27.2 ± 13.6 weeks for Hydrogel 1, 31.5 ± 17.2 weeks for Hydrogel 2) were higher in comparison to the commercially available HA hydrogel (21.4 ± 12.0 weeks), although differences were not significant. The sphericity parameter was used for evaluation of the deposit geometry. While on the injection day the sphericities were similar (~0.75 ± 0.04), at later time points significant differences between the different test substances were found (T24: PRV 0.59 ± 0.09, Hydrogel 1 0.70 ± 0.11, Hydrogel 2 0.78 ± 0.07; p ≤ 0.012 for all pairs). This study shows the applicability of OCT imaging for quantitative assessment of the volumetric behavior of intradermal deposits in vivo.

Optical coherence angiography for pre-treatment assessment and treatment monitoring following photodynamic therapy: a basal cell carcinoma patient study

Microvascular networks of human basal cell carcinomas (BCC) and surrounding skin were assessed with optical coherence angiography (OCA) in conjunction with photodynamic therapy (PDT). OCA images were collected and analyzed in 31 lesions pre-treatment, and immediately/24 hours/3-12 months post-treatment. Pre-treatment OCA enabled differentiation between prevalent subtypes of BCC (nodular and superficial) and nodular-with-necrotic-core BCC subtypes with a diagnostic accuracy of 78%; this can facilitate more accurate biopsy reducing sampling error and better therapy regimen selection. Post-treatment OCA images at 24 hours were 98% predictive of eventual outcome. Additional findings highlight the importance of pre-treatment necrotic core, vascular metrics associated with hypertrophic scar formation, and early microvascular changes necessary in both tumorous and peri-tumorous regions to ensure treatment success.

In Vivo Reflection-Mode Photoacoustic Microscopy Enhanced by Plasmonic Sensing with an Acoustic Cavity

Relying on high-sensitivity refractive index sensing and a highly constrained evanescent field of surface plasmon resonance (SPR), broadband photoacoustic (PA) pressure transients were measured using an SPR sensor instead of routinely used piezoelectric ultrasonic transducers. An acoustic cavity made from stainless steel and having a designed ellipsoidal inner surface redirected laser-induced PA waves from the PA excitation spot to the SPR sensor. By incorporating the SPR sensor with the acoustic cavity, we developed optical-resolution photoacoustic microscopy (OR-PAM) with multiple advantages, including reflection-mode signal capture, improved PA detection sensitivity, increased PA spectral bandwidth as broad as ∼98 MHz, and micrometer-scale lateral resolution. This allowed label-free volumetric PA imaging of vasculature in not only the thin ear but also the thick forelimb of living mice. With these combined advantages, our OR-PAM system potentially offers more opportunities for biomedical investigation, for example, when studying microcirculations in the eye and cortex.

Optical coherence tomography angiography and photoacoustic imaging in dermatology

Optical coherence tomography angiography (OCTA) is a relatively novel functional extension of the widely accepted ophthalmic imaging tool named optical coherence tomography (OCT). Since OCTA's debut in ophthalmology, researchers have also been trying to expand its translational application in dermatology. The ability of OCTA to resolve microvasculature has shown promising results in imaging skin diseases. Meanwhile, photoacoustic imaging (PAI), which uses laser pulse induced ultrasound waves as the signal, has been studied to differentiate human skin layers and to help in skin disease diagnosis. This perspective article gives a short review of OCTA and PAI in the field of photodermatology. After an introduction to the principles of OCTA and PAI, we describe the most updated results of skin disease imaging using these two optical imaging modalities. We also place emphasis on dual modality imaging combining OCTA and photoacoustic tomography (PAT) for dermatological applications. In the end, the challenges and prospects of these two imaging modalities in dermatology are discussed.

Engineering blood vessels and vascularized tissues: technology trends and potential clinical applications

Vascular tissue engineering has the potential to make a significant impact on the treatment of a wide variety of medical conditions, including providing in vitro generated vascularized tissue and organ constructs for transplantation. Since the first report on the construction of a biological blood vessel, significant research and technological advances have led to the generation of clinically relevant large and small diameter tissue engineered vascular grafts (TEVGs). However, developing a biocompatible blood-contacting surface is still a major challenge. Researchers are using biomimicry to generate functional vascular grafts and vascular networks. A multi-disciplinary approach is being used that includes biomaterials, cells, pro-angiogenic factors and microfabrication technologies. Techniques to achieve spatiotemporal control of vascularization include use of topographical engineering and controlled-release of growth/pro-angiogenic factors. Use of decellularized natural scaffolds has gained popularity for engineering complex vascularized organs for potential clinical use. Pre-vascularization of constructs prior to implantation has also been shown to enhance its anastomosis after implantation. Host-implant anastomosis is a phenomenon that is still not fully understood. However, it will be a critical factor in determining the in vivo success of a TEVGs or bioengineered organ. Many clinical studies have been conducted using TEVGs, but vascularized tissue/organ constructs are still in the research & development stage. In addition to technical challenges, there are commercialization and regulatory challenges that need to be addressed. In this review we examine recent advances in the field of vascular tissue engineering, with a focus on technology trends, challenges and potential clinical applications.

Automated registration of magnetic resonance imaging and optoacoustic tomography data for experimental studies

Multimodal imaging combining optoacoustic tomography (OAT) with magnetic resonance imaging (MRI) enables spatiotemporal resolution complementarity, improves accurate quantification, and thus yields more insights into physiology and pathophysiology. However, only manual landmark based coregistration of OAT-MRI has been used so far. We developed a toolbox (RegOA), which frames an automated registration pipeline to align OAT with high-field MR images based on mutual information. We assessed the performance of the registration method using images acquired on one phantom with fiducial markers and in vivo/ex vivo data of mouse heads/brain. The accuracy and robustness of the registration are improved using a two-step registration method with preprocessing of OAT and MRI data. The major advantages of our approach are minimal user input and quantitative assessment of the registration error. The registration with MR and standard reference atlas enables regional information extraction, facilitating the accurate, objective, and rapid analysis of large groups of rodent OAT and MR images.

Cooperative Three-View Imaging Optical Coherence Tomography for Intraoperative Vascular Evaluation

Real-time intraoperative optical coherence tomography (OCT) imaging of blood vessels after anastomosis operation can provide important information the vessel, such as patency, flow speed, and thrombosis morphology. Due to the strong scattering and absorption effect of blood, normal OCT imaging suffers from the problem of incomplete cross-sectional view of the vessel under investigation when the diameter is large. In this work, we present a novel cooperative three-view imaging spectral domain optical coherence tomography system for intraoperative exposed vascular imaging. Two more side views (left view and right view) were realized through a customized sample arm optical design and corresponding mechanical design and fabrication, which could generate cross-sectional images from three circumferential view directions to achieve a larger synthetic field of view (FOV). For each view, the imaging depth was 6.7 mm (in air) and the lateral scanning range was designed to be 3 mm. Therefore, a shared synthetic rectangle FOV of 3 mm × 3 mm was achieved through cooperative three view scanning. This multi-view imaging method can meet the circumferential imaging demands of vessels with an outer diameter less than 3 mm. Both phantom tube and rat vessel imaging confirmed the increased system FOV performance. We believe the intraoperative application of this cooperative three-imaging optical coherence tomography for objective vascular anastomosis evaluation can benefit patient outcomes in the future.

Integrated approaches to spatiotemporally directing angiogenesis in host and engineered tissues

The field of tissue engineering has turned towards biomimicry to solve the problem of tissue oxygenation and nutrient/waste exchange through the development of vasculature. Induction of angiogenesis and subsequent development of a vascular bed in engineered tissues is actively being pursued through combinations of physical and chemical cues, notably through the presentation of topographies and growth factors. Presenting angiogenic signals in a spatiotemporal fashion is beginning to generate improved vascular networks, which will allow for the creation of large and dense engineered tissues. This review provides a brief background on the cells, mechanisms, and molecules driving vascular development (including angiogenesis), followed by how biomaterials and growth factors can be used to direct vessel formation and maturation. Techniques to accomplish spatiotemporal control of vascularization include incorporation or encapsulation of growth factors, topographical engineering, and 3D bioprinting. The vascularization of engineered tissues and their application in angiogenic therapy in vivo is reviewed herein with an emphasis on the most densely vascularized tissue of the human body - the heart.

STATEMENT OF SIGNIFICANCE

Vascularization is vital to wound healing and tissue regeneration, and development of hierarchical networks enables efficient nutrient transfer. In tissue engineering, vascularization is necessary to support physiologically dense engineered tissues, and thus the field seeks to induce vascular formation using biomaterials and chemical signals to provide appropriate, pro-angiogenic signals for cells. This review critically examines the materials and techniques used to generate scaffolds with spatiotemporal cues to direct vascularization in engineered and host tissues in vitro and in vivo. Assessment of the field's progress is intended to inspire vascular applications across all forms of tissue engineering with a specific focus on highlighting the nuances of cardiac tissue engineering for the greater regenerative medicine community.

Non-invasive multimodal optical coherence and photoacoustic tomography for human skin imaging

The cutaneous vasculature is involved in many diseases. Current clinical examination techniques, however, cannot resolve the human vasculature with all plexus in a non-invasive manner. By combining an optical coherence tomography system with angiography extension and an all optical photoacoustic tomography system, we can resolve in 3D the blood vessels in human skin for all plexus non-invasively. With a customized imaging unit that permits access to various parts of patients' bodies, we applied our multimodality imaging system to investigate several different types of skin conditions. Quantitative vascular analysis is given for each of the dermatological conditions to show the potential diagnostic value of our system in non-invasive examination of diseases and physiological processes. Improved performance of our system over its previous generation is also demonstrated with an updated characterization.

Long ranging swept-source optical coherence tomography-based angiography outperforms its spectral-domain counterpart in imaging human skin microcirculations

There is an increasing demand for imaging tools in clinical dermatology that can perform in vivo wide-field morphological and functional examination from surface to deep tissue regions at various skin sites of the human body. The conventional spectral-domain optical coherence tomography-based angiography (SD-OCTA) system is difficult to meet these requirements due to its fundamental limitations of the sensitivity roll-off, imaging range as well as imaging speed. To mitigate these issues, we demonstrate a swept-source OCTA (SS-OCTA) system by employing a swept source based on a vertical cavity surface-emitting laser. A series of comparisons between SS-OCTA and SD-OCTA are conducted. Benefiting from the high system sensitivity, long imaging range, and superior roll-off performance, the SS-OCTA system is demonstrated with better performance in imaging human skin than the SD-OCTA system. We show that the SS-OCTA permits remarkable deep visualization of both structure and vasculature (up to ∼2  mm penetration) with wide field of view capability (up to 18×18  mm2), enabling a more comprehensive assessment of the morphological features as well as functional blood vessel networks from the superficial epidermal to deep dermal layers. It is expected that the advantages of the SS-OCTA system will provide a ground for clinical translation, benefiting the existing dermatological practice.

Optical Coherence Microscopy

The present chapter aims at demonstrating the capabilities of optical coherence microscopy (OCM) for applications in biomedical imaging. We furthermore review the functional imaging capabilities of OCM focusing on lable-free optical angiography. We conclude with a section on digital wavefront control and a short outlook on future developments, in particular for contrast enhancement techniques.

Intraoperative assessment of laryngeal pathologies with optical coherence tomography integrated into a surgical microscope

OBJECTIVE

Endoscopic examination followed by tissue biopsy is the gold standard in the evaluation of lesions of the upper aerodigestive tract. However, it can be difficult to distinguish between healthy mucosa, dysplasia, and invasive carcinoma. Optical coherence tomography (OCT) is a non-invasive technique which acquires high-resolution, cross-sectional images of tissue in vivo. Integrated into a surgical microscope, it allows the intraoperative evaluation of lesions simultaneously with microscopic visualization.

STUDY DESIGN

In a prospective case series, we evaluated the use of OCT integrated into a surgical microscope during microlaryngoscopy to help differentiating various laryngeal pathologies.

METHODS

33 patients with laryngeal pathologies were examined with an OCT- microscope (OPMedT iOCT-camera, HS Hi-R 1000G-microscope, Haag-Streit Surgical GmbH, Wedel, Germany) during microlaryngoscopy. The suspected intraoperative diagnoses were compared to the histopathological reports of subsequent tissue biopsies.

RESULTS

Hands-free non-contact OCT revealed high-resolution images of the larynx with a varying penetration depth of up to 1.2 mm and an average of 0.6 mm. Picture quality was variable. OCT showed disorders of horizontal tissue layering in dysplasias with a disruption of the basement membrane in carcinomas. When comparing the suspected diagnosis during OCT-supported microlaryngoscopy with histology, 79% of the laryngeal lesions could be correctly identified. Premalignant lesions were difficult to diagnose and falsely classified as carcinoma.

CONCLUSION

OCT integrated into a surgical microscope seems to be a promising adjunct tool to discriminate pathologies of the upper aerodigestive tract intraoperatively. However, picture quality and penetration depth were variable. Although premalignant lesions were difficult to diagnose, the system proved overall helpful for the intraoperative discrimination of benign and malignant tumors. Further studies will be necessary to define its value in the future. Lasers Surg. Med. 49:490-497, 2017. © 2017 Wiley Periodicals, Inc.

Optical Coherence Tomography Angiography: A New Tool in Glaucoma Diagnostics and Research

Optical coherence tomography angiography (OCTA) is a new modality in ocular imaging which provides high resolution view of the vascular structures in the retina and optic nerve head. This technology has the advantages of being noninvasive, rapid and reproducible. OCTA is becoming a valuable tool for evaluating many retinal and optic nerve diseases. This article provides a brief introduction to the technology and its application in the field of glaucoma diagnostics.

Comprehensive vascular imaging using optical coherence tomography-based angiography and photoacoustic tomography

Studies have proven the relationship between cutaneous vasculature abnormalities and dermatological disorders, but to image vasculature noninvasively <italic<in vivo</italic<, advanced optical imaging techniques are required. In this study, we imaged a palm of a healthy volunteer and three subjects with cutaneous abnormalities with photoacoustic tomography (PAT) and optical coherence tomography with angiography extension (OCTA). Capillaries in the papillary dermis that are too small to be discerned with PAT are visualized with OCTA. From our results, we speculate that the PA signal from the palm is mostly from hemoglobin in capillaries rather than melanin, knowing that melanin concentration in volar skin is significantly smaller than that in other areas of the skin. We present for the first time OCTA images of capillaries along with the PAT images of the deeper vessels, demonstrating the complementary effective imaging depth range and the visualization capabilities of PAT and OCTA for imaging human skin <italic<in vivo</italic<. The proposed imaging system in this study could significantly improve treatment monitoring of dermatological diseases associated with cutaneous vasculature abnormalities.