Optical clearing in photoacoustic flow cytometry

Light in evaluation of molecular diffusion in tissues: Discrimination of pathologies

The evaluation of the diffusion properties of different molecules in tissues is a subject of great interest in various fields, such as dermatology/cosmetology, clinical medicine, implantology and food preservation. In this review, a discussion of recent studies that used kinetic spectroscopy measurements to evaluate such diffusion properties in various tissues is made. By immersing ex vivo tissues in agents or by topical application of those agents in vivo, their diffusion properties can be evaluated by kinetic collimated transmittance or diffuse reflectance spectroscopy. Using this method, recent studies were able to discriminate the diffusion properties of agents between healthy and diseased tissues, especially in the cases of cancer and diabetes mellitus. In the case of cancer, it was also possible to evaluate an increase of 5% in the mobile water content from the healthy to the cancerous colorectal and kidney tissues. Considering the application of some agents to living organisms or food products to protect them from deterioration during low temperature preservation (cryopreservation), and knowing that such agent inclusion may be reversed, some studies in these fields are also discussed. Considering the broadband application of the optical spectroscopy evaluation of the diffusion properties of agents in tissues and the physiological diagnostic data that such method can acquire, further studies concerning the optimization of fruit sweetness or evaluation of poison diffusion in tissues or antidote application for treatment optimization purposes are indicated as future perspectives.

Photoacoustic imaging for cutaneous melanoma assessment: a comprehensive review

Significance

Cutaneous melanoma (CM) has a high morbidity and mortality rate, but it can be cured if the primary lesion is detected and treated at an early stage. Imaging techniques such as photoacoustic (PA) imaging (PAI) have been studied and implemented to aid in the detection and diagnosis of CM.

Aim

Provide an overview of different PAI systems and applications for the study of CM, including the determination of tumor depth/thickness, cancer-related angiogenesis, metastases to lymph nodes, circulating tumor cells (CTCs), virtual histology, and studies using exogenous contrast agents.

Approach

A systematic review and classification of different PAI configurations was conducted based on their specific applications for melanoma detection. This review encompasses animal and preclinical studies, offering insights into the future potential of PAI in melanoma diagnosis in the clinic.

Results

PAI holds great clinical potential as a noninvasive technique for melanoma detection and disease management. PA microscopy has predominantly been used to image and study angiogenesis surrounding tumors and provide information on tumor characteristics. Additionally, PA tomography, with its increased penetration depth, has demonstrated its ability to assess melanoma thickness. Both modalities have shown promise in detecting metastases to lymph nodes and CTCs, and an all-optical implementation has been developed to perform virtual histology analyses. Animal and human studies have successfully shown the capability of PAI to detect, visualize, classify, and stage CM.

Conclusions

PAI is a promising technique for assessing the status of the skin without a surgical procedure. The capability of the modality to image microvasculature, visualize tumor boundaries, detect metastases in lymph nodes, perform fast and label-free histology, and identify CTCs could aid in the early diagnosis and classification of CM, including determination of metastatic status. In addition, it could be useful for monitoring treatment efficacy noninvasively.

In vivo skin optical clearing for improving imaging and light-induced therapy: a review

Significance

Skin is the largest organ and also the first barrier of body. Skin diseases are common, and cutaneous microcirculation is relative to various diseases. Researchers attempt to develop novel imaging techniques to obtain the complex structure, components, and functions of skin. Modern optical techniques provide a powerful tool with non-invasiveness, but the imaging performance suffers from the turbid character of skin. In vivo skin optical clearing technique has been proposed to reduce tissue scattering and enhance penetration depth of light and became a hot topic of research.

Aim

The aim of this review is to provide a comprehensive overview of recent development of in vivo skin optical clearing methods, how in vivo skin optical clearing enhances imaging performance, and its applications in study and light therapy of various diseases.

Approach

Based on the references published over the last decade, the important milestones on the mechanism, methods, and its fundamental and clinical applications of in vivo skin optical clearing technique are provided.

Results

With the deepening understanding of skin optical clearing mechanisms, efficient in vivo skin optical clearing methods were constantly screened out. These methods have been combined with various optical imaging techniques to improve imaging performances and acquire deeper and finer skin-related information. In addition, in vivo skin optical clearing technique has been widely applied in assisting study of diseases as well as achieving safe, high-efficiency light-induced therapy.

Conclusions

In the last decade, in vivo skin optical clearing technique has developed rapidly and played an important role in skin-related studies.

Confocal Raman Micro-Spectroscopy for Discrimination of Glycerol Diffusivity in Ex Vivo Porcine Dura Mater

Dura mater (DM) is a connective tissue with dense collagen, which is a protective membrane surrounding the human brain. The optical clearing (OC) method was used to make DM more transparent, thereby allowing to increase in-depth investigation by confocal Raman micro-spectroscopy and estimate the diffusivity of 50% glycerol and water migration. Glycerol concentration was obtained, and the diffusion coefficient was calculated, which ranged from 9.6 × 10-6 to 3.0 × 10-5 cm2/s. Collagen-related Raman band intensities were significantly increased for all depths from 50 to 200 µm after treatment. In addition, the changes in water content during OC showed that 50% glycerol induces tissue dehydration. Weakly and strongly bound water types were found to be most concentrated, playing a major role in the glycerol-induced water flux and OC. Results show that OC is an efficient method for controlling the DM optical properties, thereby enhancing the in-depth probing for laser therapy and diagnostics of the brain. DM is a comparable to various collagen-containing tissues and organs, such as sclera of eyes and skin dermis.

Ex vivo confocal Raman microspectroscopy of porcine dura mater supported by optical clearing

The effect of tissue optical clearing (TOC) to increase the probing depth and observe in-depth structure of the ex vivo porcine dura mater was studied by confocal Raman microspectroscopy (CRM). Raman intensities were significantly increased at the depth of 250 μm for all collagen bands after treatment with glycerol. The influence of glycerol on collagen hydration was also investigated. The results indicate that the process of TOC can be divided into three main steps. The first one is a fast process of tissue dehydration accompanied by collagen shrinkage while the second relatively slow process is related to the glycerol penetration into the interfibrillar space of collagen combined with swelling of tissue. The third step is collagen dissociation caused by the high concentration of glycerol. To the best of our knowledge, this study is the first example to introduce the TOC technique in assisting CRM of ex vivo dura mater in-depth probing.

Optical clearing of tissues: Issues of antimicrobial phototherapy and drug delivery

This review presents principles and novelties in the field of tissue optical clearing (TOC) technology, as well as application for optical monitoring of drug delivery and effective antimicrobial phototherapy. TOC is based on altering the optical properties of tissue through the introduction of immersion optical cleaning agents (OCA), which impregnate the tissue of interest. We also analyze various methods and kinetics of delivery of photodynamic agents, nanoantibiotics and their mixtures with OCAs into the tissue depth in the context of antimicrobial and antifungal phototherapy. In vitro and in vivo studies of antimicrobial phototherapies, such as photodynamic, photothermal plasmonic and photocatalytic, are summarized, and the prospects of a new TOC technology for effective killing of pathogens are discussed.

Optical clearing for photoacoustic lympho- and angiography beyond conventional depth limit in vivo

Photoacoustic (PA) imaging (PAI) is an emerging powerful tool for noninvasive real-time mapping of blood and lymphatic vessels and lymph nodes in vivo to diagnose cancer, lymphedema and other diseases. Among different PAI instruments, commercially available raster-scanning optoacoustic mesoscopy (RSOM) (iThera Medical GmbH., Germany) is useful for high-resolution imaging of different tissues with high potential of clinical translation. However, skin light scattering prevents mapping vessels and nodes deeper than 1-2 mm, that limits diagnostic values of PAI including RSOM. Here we demonstrate that glycerol-based tissue optical clearing (TOC) overcomes this challenge by reducing light scattering that improves RSOM depth penetration. In preclinical model of mouse limb in vivo, the replacement of conventional acoustic coupling agents such as water on the mixture of 70 % glycerol and 30 % ultrasound (US) gel resulted in the increase of tissue imaging depth in 1.5-2 times with 3D visualization of vessels with diameter down to 20 μm. To distinguish blood and lymphatic networks, we integrated label-free PA angiography (i.e., imaging of blood vessels), which uses hemoglobin as endogenous contrast agent, with PA lymphography based on labeling of lymphatic vessels with exogenous PA contrast agents. Similar to well-established clinical lymphography, contrast agents were injected in tissue and taken up by lymphatic vessels within a few minutes that provided quick RSOM lymphography. Furthermore, co-injection of PA contrast dye and multilayer nanocomposites as potential low-toxic drug-cargo showed selective prolonged accumulation of nanocomposites in sentinel lymph nodes. Overall, our findings open perspectives for deep and high resolution 3D PA angio- and lymphography, and for PA-guided lymphatic drug delivery using new RSOM & TOC approach.

Rapid Ultrasound Optical Clearing of Human Light and Dark Skin

Application of optical clearing of biological tissue in humans in vivo is challenging due to toxicity of chemical agents, long processing time (≥30 min), and moderate (1.3-1.5-fold) imaging depth improvement. Here, we introduce novel, robust, and rapid ultrasound-based optical clearing of human skin without chemical agents that provides dramatic (up to 10-fold) reducing processing time down to 2-5 min. We discovered that ultrasound alone can increase a light depth penetration for optical coherence tomography (OCT) up to ~1.5-fold during 2 min. Nevertheless, sequent application of microdermabrasion, oleic acid and ultrasound allowed increasing OCT signal amplitude up to 3.3-fold with more than twice improved depth penetration during 30 min that was not demonstrated with other approaches. Comparison of these effects in light and dark skin revealed similarity of the optical clearing mechanisms. However, for combined optical clearing, only 1.34-fold increase in OCT signal amplitude was achieved for dark skin.

Biomedical Applications of Tissue Clearing and Three-Dimensional Imaging in Health and Disease

Three-dimensional (3D) optical imaging techniques can expand our knowledge about physiological and pathological processes that cannot be fully understood with 2D approaches. Standard diagnostic tests frequently are not sufficient to unequivocally determine the presence of a pathological condition. Whole-organ optical imaging requires tissue transparency, which can be achieved by using tissue clearing procedures enabling deeper image acquisition and therefore making possible the analysis of large-scale biological tissue samples. Here, we review currently available clearing agents, methods, and their application in imaging of physiological or pathological conditions in different animal and human organs. We also compare different optical tissue clearing methods discussing their advantages and disadvantages and review the use of different 3D imaging techniques for the visualization and image acquisition of cleared tissues. The use of optical tissue clearing resources for large-scale biological tissues 3D imaging paves the way for future applications in translational and clinical research.

Designing the Uniform Stochastic Photomatrix Therapeutic Systems

Photomatrix therapeutic systems (PMTS) are widely used for the tasks of preventive, stimulating and rehabilitation medicine. They consist of low-intensity light-emitting diodes (LEDs) having the quasi-monochromatic irradiation properties. Depending on the LED matrix structures, PMTS are intended to be used for local and large areas of bio-objects. However, in the case of non-uniform irradiation of biological tissues, there is a risk of an inadequate physiological response to this type of exposure. The proposed approach considers a novel technique for designing this type of biomedical technical systems, which use the capabilities of stochastic algorithms for LED switching. As a result, the use of stochastic photomatrix systems based on the technology of uniform twisting generation of random variables significantly expands the possibilities of their medical application.

Experimental studies of optoacoustic effect on the model of erythrocytes in the presence of carbon nanoparticles

Experimental model has been developed to study optoacoustic signal from model blood cells presented by polystyrene microspheres with nanoparticles. It was found out that nanoparticles due to their strong absorption of light significantly affect the coefficient of cellular optical absorption, while the thermophysical parameters, namely the coefficient of thermal expansion, compressibility and isobaric specific heat of cells remain unchanged, since nanoparticles occupy a small intracellular volume compared to the cell volume. Optoacoustic signals were obtained using model solutions at various concentrations of cells and nanoparticles using 1064 nm laser. The results of experimental measurements using LIMO 100–532/1064-U system based on Nd:YAG showed that the amplitude of the optoacoustic signal increased without increasing the temperature in the laser area.

Methods for Optical Skin Clearing in Molecular Optical Imaging in Dermatology

This short review describes recent progress in using optical clearing (OC) technique in skin studies. Optical clearing is an efficient tool for enhancing the probing depth and data quality in multiphoton microscopy and Raman spectroscopy. Here, we discuss the main mechanisms of OC, its safety, advantages, and limitations. The data on the OC effect on the skin water content are presented. It was demonstrated that 70% glycerol and 100% Omnipaque^TM 300 reduce the water content in the skin. Both OC agents (OCAs) significantly affect the strongly bound and weakly bound water. However, Omnipaque^TM 300 causes considerably less skin dehydration than glycerol. In addition, the results of examination of the OC effect on autofluorescence in two-photon excitation and background fluorescence in Raman scattering at different skin depths are presented. It is shown that Omnipaque^TM 300 is a promising OCA due to its ability to reduce background fluorescence in the upper skin layers. The possibility of multimodal imaging combining optical methods and OC technique is discussed.

In vivo liquid biopsy using Cytophone platform for photoacoustic detection of circulating tumor cells in patients with melanoma

Most cancer deaths arise from metastases as a result of circulating tumor cells (CTCs) spreading from the primary tumor to vital organs. Despite progress in cancer prognosis, the role of CTCs in early disease diagnosis is unclear because of the low sensitivity of CTC assays. We demonstrate the high sensitivity of the Cytophone technology using an in vivo photoacoustic flow cytometry platform with a high pulse rate laser and focused ultrasound transducers for label-free detection of melanin-bearing CTCs in patients with melanoma. The transcutaneous delivery of laser pulses via intact skin to a blood vessel results in the generation of acoustic waves from CTCs, which are amplified by vapor nanobubbles around intrinsic melanin nanoclusters. The time-resolved detection of acoustic waves using fast signal processing algorithms makes photoacoustic data tolerant to skin pigmentation and motion. No CTC-associated signals within established thresholds were identified in 19 healthy volunteers, but 27 of 28 patients with melanoma displayed signals consistent with single, clustered, and likely rolling CTCs. The detection limit ranged down to 1 CTC/liter of blood, which is ~1000 times better than in preexisting assays. The Cytophone could detect individual CTCs at a concentration of ≥1 CTC/ml in 20 s and could also identify clots and CTC-clot emboli. The in vivo results were verified with six ex vivo methods. These data suggest the potential of in vivo blood testing with the Cytophone for early melanoma screening, assessment of disease recurrence, and monitoring of the physical destruction of CTCs through real-time CTC counting.

Poisson Twister Generator by Cumulative Frequency Technology

The widely known generators of Poisson random variables are associated with different modifications of the algorithm based on the convergence in probability of a sequence of uniform random variables to the created stochastic number. However, in some situations, this approach yields different discrete Poisson probability distributions and skipping in the generated numbers. This article offers a new approach for creating Poisson random variables based on the complete twister generator of uniform random variables, using cumulative frequency technology. The simulation results confirm that probabilistic and frequency distributions of the obtained stochastic numbers completely coincide with the theoretical Poisson distribution. Moreover, combining this new approach with the tuning algorithm of basic twister generation allows for a significant increase in length of the created sequences without using additional RAM of the computer.

Noninvasive label-free detection of circulating white and red blood clots in deep vessels with a focused photoacoustic probe

Blood clotting is a serious clinical complication of many medical procedures and disorders including surgery, catheterization, transplantation, extracorporeal circuits, infections, and cancer. This complication leads to high patient morbidity and mortality due to clot-induced pulmonary embolism, stroke, and in some cases heart attack. Despite the clear medical significance, little progress has been made in developing the methods for detection of circulating blood clots (CBCs), also called emboli. We recently demonstrated the application of in vivo photoacoustic (PA) flow cytometry (PAFC) with unfocused ultrasound transducers for detection of CBCs in small vessels in a mouse model. In the current study, we extend applicability of PAFC for detection of CBCs in relatively large (1.5-2 mm) and deep (up to 5-6 mm) blood vessels in rat and rabbit models using a high pulse rate 1064 nm laser and focused ultrasound transducer with a central hole for an optic fiber. Employing phantoms and chemical activation of clotting, we demonstrated PA identification of white, red, and mixed CBCs producing negative, positive, and mixed PA contrast in blood background, respectively. We confirmed that PAFC can detect both red and white CBCs induced by microsurgical procedures, such as a needle or catheter insertion, as well as stroke modeled by injection of artificial clots. Our results show great potential for a PAFC diagnostic platform with a wearable PA fiber probe for diagnosis of thrombosis and embolism in vivo that is impossible with existing techniques.

Dynamic blood flow phantom with negative and positive photoacoustic contrasts

In vivo photoacoustic (PA) flow cytometry (PAFC) has great clinical potential for early, noninvasive diagnosis of cancer, infections (e.g., malaria and bacteremia), sickle anemia, and cardiovascular disorders, including stroke prevention through detection of circulating white clots with negative PA contrast. For clinical applications, this diagnostic platform still requires optimization and calibration. We have already demonstrated that this need can be partially addressed by in vivo examination of large mouse blood vessels, which are similar to human vessels used. Here, we present an alternative method for PAFC optimization that utilizes novel, clinically relevant phantoms resembling pigmented skin, tissue, vessels, and flowing blood. This phantom consists of a scattering-absorbing medium with a melanin layer and plastic tube with flowing beads to model light-absorbing red blood cells (RBCs) and circulating tumor cells (CTCs), as well as transparent beads to model white blood cells and clots. Using a laser diode, we demonstrated the extraordinary ability of PAFC to dynamically detect fast-moving mimic CTCs with positive PA contrast and white clots with negative PA contrast in an RBC background. Time-resolved detection of the delayed PA signals from blood vessels demonstrated complete suppression of the PA background from the modeled pigmented skin. This novel, medically relevant, dynamic blood flow phantom can be used to calibrate and maintain PAFC parameters for routine clinical applications.

Measurement of tissue optical properties in the context of tissue optical clearing

Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

Current status, pitfalls and future directions in the diagnosis and therapy of lymphatic malformation

Lymphatic malformations are complex congenital vascular lesions composed of dilated, abnormal lymphatic channels of varying size that can result in significant esthetic and physical impairment due to relentless growth. Lymphatic malformations comprised of micro-lymphatic channels (microcystic) integrate and infiltrate normal soft tissue, leading to a locally invasive mass. Ultrasonography and magnetic resonance imaging assist in the diagnosis but are unable to detect microvasculature present in microcystic lymphatic malformations. In this review, we examine existing tools and elaborate on alternative diagnostic methods in assessing lymphatic malformations. In particular, photoacoustics, low-toxicity nanoparticles and optical clearing can overcome existing challenges in the examination of lymphatic channels in vivo. In combination with photothermal scanning and flow cytometry, Photoacoustic techniques may provide a versatile tool for lymphatic-related clinical applications, potentially leading to a single diagnostic and therapeutic platform to overcome limitations in current imaging techniques and permit targeted theranostics of microcystic lymphatic malformations.

Cell-Based Drug Delivery and Use of Nano-and Microcarriers for Cell Functionalization

Cell functionalization with recently developed various nano- and microcarriers for therapeutics has significantly expanded the application of cell therapy and targeted drug delivery for the effective treatment of a number of diseases. The aim of this progress report is to review the most recent advances in cell-based drug vehicles designed as biological transporter platforms for the targeted delivery of different drugs. For the design of cell-based drug vehicles, different pathways of cell functionalization, such as covalent and noncovalent surface modifications, internalization of carriers are considered in greater detail together with approaches for cell visualization in vivo. In addition, several animal models for the study of cell-assisted drug delivery are discussed. Finally, possible future developments and applications of cell-assisted drug vehicles toward targeted transport of drugs to a designated location with no or minimal immune response and toxicity are addressed in light of new pathways in the field of nanomedicine.

FSOCA-induced switchable footpad skin optical clearing window for blood flow and cell imaging in vivo

The mouse footpad for its feature of hairlessness provides an available window for imaging vascular and cellular structure and function in vivo. Unfortunately, the strong scattering of its skin limits the penetration of light and reduces the imaging contrast and depth. Herein, an innovative footpad skin optical clearing agent (FSOCA) was developed to make the footpad skin transparent quickly by topical application. The results demonstrate that FSOCA treatment not only allowed the cutaneous blood vessels and blood flow distribution to be monitored by laser speckle contrast imaging technique with higher contrast, but also permitted the fluorescent cells to be imaged by laser scanning confocal microscopy with higher fluorescence signal intensity and larger imaging depth. In addition, the physiological saline-treatment could make the footpad skin recover to the initial turbid status, and reclearing would not induce any adverse effects on the distributions and morphologies of blood vessels and cells, which demonstrated a safe and switchable window for biomedical imaging. This switchable footpad skin optical clearing window will be significant for studying blood flow dynamics and cellular immune function in vivo in some vascular and immunological diseases. Picture: Repeated cell imaging in vivo before (a) and after (b) FSOCA treatment. (c) Merged images of 4 h (cyan border) or 72 h (magenta border) over 0 h. (d) Zoom of ROI in 4 h (yellow rectangle) or 72 h (red rectangle).

In vivo noninvasive analysis of graphene nanomaterial pharmacokinetics using photoacoustic flow cytometry

Graphene-based nanomaterials (GBNs) are quickly revolutionizing modern electronics, energy generation and storage, clothing and biomedical devices. Due to GBN's variety of physical and chemical parameters that define their toxicity and their aggregation in suspension, interpreting its toxicology without accurate information on graphene's distribution and behavior in live organisms is challenging. In this work, we present a laser-based optical detection methodology for noninvasive detection and pharmacokinetics analysis of GBNs directly in blood flow in mice using in vivo photoacoustic (PA) flow cytometry (PAFC). PAFC provides unique insight on how chemical modifications of GBNs affect their distribution in blood circulation and how quickly they are eliminated from the flow. Overall, PAFC provided unique data crucial for understanding GBN toxicity through real-time detection of GBNs using their intrinsic light absorption contrast. Copyright © 2017 John Wiley & Sons, Ltd.

Photoacoustic Flow Cytometry for Single Sickle Cell Detection In Vitro and In Vivo

Control of sickle cell disease (SCD) stage and treatment efficiency are still time-consuming which makes well-timed prevention of SCD crisis difficult. We show here that in vivo photoacoustic (PA) flow cytometry (PAFC) has a potential for real-time monitoring of circulating sickled cells in mouse model. In vivo data were verified by in vitro PAFC and photothermal (PT) and PA spectral imaging of sickle red blood cells (sRBCs) expressing SCD-associated hemoglobin (HbS) compared to normal red blood cells (nRBCs). We discovered that PT and PA signal amplitudes from sRBCs in linear mode were 2–4-fold lower than those from nRBCs. PT and PA imaging revealed more profound spatial hemoglobin heterogeneity in sRBCs than in nRBCs, which can be associated with the presence of HbS clusters with high local absorption. This hypothesis was confirmed in nonlinear mode through nanobubble formation around overheated HbS clusters accompanied by spatially selective signal amplification. More profound differences in absorption of sRBCs than in nRBCs led to notable increase in PA signal fluctuation (fluctuation PAFC mode) as an indicator of SCD. The obtained data suggest that noninvasive label-free fluctuation PAFC has a potential for real-time enumeration of sRBCs both in vitro and in vivo.

Preclinical photoacoustic models: application for ultrasensitive single cell malaria diagnosis in large vein and artery

In vivo photoacoustic flow cytometry (PAFC) has demonstrated potential for early diagnosis of deadly diseases through detection of rare circulating tumor cells, pathogens, and clots in nearly the entire blood volume. Before clinical application, this promising diagnostic platform requires verification and optimization using adequate preclinical models. We show here that this can be addressed by examination of large mouse blood vessels which are similar in size, depth and flow velocity to human vessels used in PAFC. Using this model, we verified the capability of PAFC for ultrasensitive, noninvasive, label-free, rapid malaria diagnosis. The time-resolved detection of delayed PA signals from deep vessels provided complete elimination of background from strongly pigmented skin. We discovered that PAFC's sensitivity is higher during examination of infected cells in arteries compared to veins at similar flow rate. Our advanced PAFC platform integrating a 1060 nm laser with tunable pulse rate and width, a wearable probe with a focused transducer, and linear and nonlinear nanobubble-amplified signal processing demonstrated detection of parasitemia at the unprecedented level of 0.00000001% within 20 seconds and the potential to further improve the sensitivity 100-fold in humans, that is approximately 10⁶ times better than in existing malaria tests.

Skull Optical Clearing Solution for Enhancing Ultrasonic and Photoacoustic Imaging

The performance of photoacoustic microscopy (PAM) degrades due to the turbidity of the skull that introduces attenuation and distortion of both laser and stimulated ultrasound. In this manuscript, we demonstrated that a newly developed skull optical clearing solution (SOCS) could enhance not only the transmittance of light, but also that of ultrasound in the skull in vitro. Thus the photoacoustic signal was effectively elevated, and the relative strength of the artifacts induced by the skull could be suppressed. Furthermore in vivo studies demonstrated that SOCS could drastically enhance the performance of photoacoustic microscopy for cerebral microvasculature imaging.

Optical clearing of skin enhanced with hyaluronic acid for increased contrast of optoacoustic imaging

Enhanced delivery of optical clearing agents (OCA) through skin may improve sensitivity of optical and optoacoustic (OA) methods of imaging, sensing, and monitoring. This report describes a two-step method for enhancement of light penetration through skin. Here, we demonstrate that topical application of hyaluronic acid (HA) improves skin penetration of hydrophilic and lipophilic OCA and thus enhances their performance. We examined the OC effect of 100% polyethylene and polypropylene glycols (PPGs) and their mixture after pretreatment by HA, and demonstrated significant increase in efficiency of light penetration through skin. Increased light transmission resulted in a significant increase of OA image contrast in vitro. Topical pretreatment of skin for about 30 min with 0.5% HA in aqueous solution offers effective delivery of low molecular weight OCA such as a mixture of PPG-425 and polyethylene glycol (PEG)-400. The developed approach of pretreatment by HA prior to application of clearing agents (PEG and PPG) resulted in a ∼ 47-fold increase in transmission of red and near-infrared light and significantly enhanced contrast of OA images.

Real-Time Label-Free Embolus Detection Using In Vivo Photoacoustic Flow Cytometry

Thromboembolic events are one of the world's leading causes of death among patients. Embolus or clot formations have several etiologies including paraneoplastic, post-surgery, cauterization, transplantation, or extracorporeal circuits. Despite its medical significance, little progress has been made in early embolus detection, screening and control. The aim of our study is to test the utility of the in vivo photoacoustic (PA) flow cytometry (PAFC) technique for non-invasive embolus detection in real-time. Using in vivo PAFC, emboli were non-invasively monitored in the bloodstream of two different mouse models. The tumor-free mouse model consisted of two groups, one in which the limbs were clamped to produce vessel stasis (7 procedures), and one where the mice underwent surgery (7 procedures). The melanoma-bearing mouse model also consisted of two groups, one in which the implanted tumor underwent compression (8 procedures), and one where a surgical excision of the implanted tumor was performed (8 procedures). We demonstrated that the PAFC can detect a single embolus, and has the ability to distinguish between erythrocyte-rich (red) and leukocyte/platelet-rich (white) emboli in small vessels. We show that, in tumor-bearing mice, the level of circulating emboli was increased compared to tumor-free mice (p = 0.0013). The number of circulating emboli temporarily increased in the tumor-free control mice during vessel stasis (p = 0.033) and after surgical excisions (signed-rank p = 0.031). Similar observations were noted during tumor compression (p = 0.013) and after tumor excisions (p = 0.012). For the first time, it was possible to detect unlabeled emboli in vivo non-invasively, and to confirm the presence of pigmented tumor cells within circulating emboli. The insight on embolus dynamics during cancer progression and medical procedures highlight the clinical potential of PAFC for early detection of cancer and surgery-induced emboli to prevent the fatal thromboembolic complications by well-timed therapy.

In vivo photoacoustic flow cytometry for early malaria diagnosis

In vivo photoacoustic (PA) flow cytometry (PAFC) has already demonstrated a great potential for the diagnosis of deadly diseases through ultrasensitive detection of rare disease-associated circulating markers in whole blood volume. Here, we demonstrate the first application of this powerful technique for early diagnosis of malaria through label-free detection of malaria parasite-produced hemozoin in infected red blood cells (iRBCs) as high-contrast PA agent. The existing malaria tests using blood smears can detect the disease at 0.001-0.1% of parasitemia. On the contrary, linear PAFC showed a potential for noninvasive malaria diagnosis at an extremely low level of parasitemia of 0.0000001%, which is ∼10(3) times better than the existing tests. Multicolor time-of-flight PAFC with high-pulse repetition rate lasers at wavelengths of 532, 671, and 820 nm demonstrated rapid spectral and spatial identification and quantitative enumeration of individual iRBCs. Integration of PAFC with fluorescence flow cytometry (FFC) provided real-time simultaneous detection of single iRBCs and parasites expressing green fluorescence proteins, respectively. A combination of linear and nonlinear nanobubble-based multicolor PAFC showed capability to real-time control therapy efficiency by counting of iRBCs before, during, and after treatment. Our results suggest that high-sensitivity, high-resolution ultrafast PAFC-FFC platform represents a powerful research tool to provide the insight on malaria progression through dynamic study of parasite-cell interactions directly in bloodstream, whereas portable hand-worn PAFC device could be broadly used in humans for early malaria diagnosis. © 2016 International Society for Advancement of Cytometry.

In vivo cell characteristic extraction and identification by photoacoustic flow cytography

We present a photoacoustic flow cytography with fast cross-sectional (B-scan) imaging to precisely identify specific cells in vivo. The B-scan imaging speed of the system is up to 200 frame/s with a lateral resolution of 1.5 μm, which allows to dynamically image the flowing cells within the microvascular. The shape, size and photoacoustic intensity of the target cells are extracted from streaming images and integrated into a standard pattern to distinguish cell types. Circulating red blood cells and melanoma cells in blood vessels are simultaneously identified on melanoma-bearing mouse model. The results demonstrate that in vivo photoacoustic flow cytography can provide cells characteristics analysis and cell type's visual identification, which will be applied for noninvasively monitoring circulating tumor cells (CTCs) and analyzing hematologic diseases.

Analysis of Human and Porcine Skin in vivo/ex vivo for Penetration of Selected Oils by Confocal Raman Microscopy

BACKGROUND

The subject of oil penetration into the skin is controversially discussed in the scientific literature.

METHODS

Confocal Raman microscopy was used for analyzing oil penetration into the skin. The following methods were applied in the study: methods based on tracking specific peaks (method 1), the nonrestricted multiple least square fit (method 2), analyzing the lipid-to-keratin peak ratio using the perpendicular drop-down cutoff procedure (method 3), and the Gaussian function-based deconvolution procedure (method 4).

RESULTS

The results obtained using methods 1, 2 and 4 show that the investigated oils do not penetrate deeper than 11 µm into human and porcine skin. Petrolatum has a prominent swelling effect on the stratum corneum (32% in vivo, 28% ex vivo), while the other oils exhibit no significant swelling effect. By using method 3, the penetration profile of oils, and especially of petrolatum, into the skin was interpreted incorrectly for various reasons that are addressed herein below.

CONCLUSION

Predominantly remaining in the uppermost corneocyte layers of the stratum corneum, topically applied oils do not reach the viable cells of the stratum spinosum. To exclude any possible mistakes when using the lipid-keratin Raman peak (2,820-3,030 cm-1), the penetration analysis should be performed using the Gaussian function-based deconvolution procedure.

Arterial Blood, Rather Than Venous Blood, is a Better Source for Circulating Melanoma Cells

Background

CTCs provide prognostic information and their application is under investigation in multiple tumor types. Of the multiple variables inherent in any such process, none is more important to outcome than the appropriateness of the sample source. To address this question, we investigated CTCs in paired peripheral venous and arterial blood specimens obtained from stage IV uveal melanoma patients.

Methods

Blood specimens were obtained from both common femoral arteries and antecubital veins in 17 uveal melanoma patients with multiple hepatic metastases for CTC measurements.

Finding

CTCs were detectable with greater frequency (100%) and in larger numbers (median 5, range 1 to 168) in all arterial blood specimens than in venous samples (52.9%; median 1, range 0 to 8). Patients with hepatic as well as extra-hepatic metastasis showed higher number of arterial CTCs, compared to patients with liver-only metastasis (p = 0.003). There was no significant association between the number of arterial CTCs and the tumor burden within the liver in patients who had liver-only metastases.

Interpretation

Our data indicate that arterial blood specimens might be a better source of circulating uveal melanoma cells. Although less conveniently processed, perhaps arterial blood should be evaluated as sample source for measurement of CTCs.

•

CTCs were detectable in 100% of arterial blood obtained from metastatic uveal melanoma patients, while only 53% of venous blood was positive for CTCs.

CTCs have been investigated to provide prognostic information in multiple tumor types. Of the multiple variables, none is more important than the appropriateness of the sample source. Blood specimens were obtained from both femoral arteries and antecubital veins in 17 uveal melanoma patients with multiple hepatic metastases. CTCs were detectable with greater frequency (100%) and in larger numbers in all arterial blood specimens than in venous samples (52.9%). Our data indicate that arterial blood specimens might be a better source of circulating uveal melanoma cells. Although less convenient, arterial blood should be evaluated as sample source for measurement of CTCs.

In Vivo Long-Term Monitoring of Circulating Tumor Cells Fluctuation during Medical Interventions

The goal of this research was to study the long-term impact of medical interventions on circulating tumor cell (CTC) dynamics. We have explored whether tumor compression, punch biopsy or tumor resection cause dissemination of CTCs into peripheral blood circulation using in vivo fluorescent flow cytometry and breast cancer-bearing mouse model inoculated with MDA-MB-231-Luc2-GFP cells in the mammary gland. Two weeks after tumor inoculation, three groups of mice were the subject of the following interventions: (1) tumor compression for 15 minutes using 400 g weight to approximate the pressure during mammography; (2) punch biopsy; or (3) surgery. The CTC dynamics were determined before, during and six weeks after these interventions. An additional group of tumor-bearing mice was used as control and did not receive an intervention. The CTC dynamics in all mice were monitored weekly for eight weeks after tumor inoculation. We determined that tumor compression did not significantly affect CTC dynamics, either during the procedure itself (P = 0.28), or during the 6-week follow-up. In the punch biopsy group, we observed a significant increase in CTC immediately after the biopsy (P = 0.02), and the rate stayed elevated up to six weeks after the procedure in comparison to the tumor control group. The CTCs in the group of mice that received a tumor resection disappeared immediately after the surgery (P = 0.03). However, CTC recurrence in small numbers was detected during six weeks after the surgery. In the future, to prevent these side effects of medical interventions, the defined dynamics of intervention-induced CTCs may be used as a basis for initiation of aggressive anti-CTC therapy at time-points of increasing CTC number.

In vivo quantitation of injected circulating tumor cells from great saphenous vein based on video-rate confocal microscopy

The number of circulating tumor cell (CTC) in the peripheral blood of cancer patients can be a valuable biomarker for cancer diagnosis and treatment monitoring. In this study, we implemented a custom-design video-rate confocal microscopy system in capable of direct visualization of fast flowing CTC at great saphenous vein (GSV) of a live animal model in vivo. Continuous acquisition of video-rate images at GSV revealed the highly dynamic time-dependent changes in the number of intravenously injected circulating tumor cells. By extracting a calibration factor through the hemocytometric analysis of intravenously injected long-circulating red blood cells, we established a novel quantitation method for CTC in whole body blood in vivo.

Accessing to arteriovenous blood flow dynamics response using combined laser speckle contrast imaging and skin optical clearing

Laser speckle contrast imaging (LSCI) shows a great potential for monitoring blood flow, but the spatial resolution suffers from the scattering of tissue. Here, we demonstrate the capability of a combination method of LSCI and skin optical clearing to describe in detail the dynamic response of cutaneous vasculature to vasoactive noradrenaline injection. Moreover, the superior resolution, contrast and sensitivity make it possible to rebuild arteries-veins separation and quantitatively assess the blood flow dynamical changes in terms of flow velocity and vascular diameter at single artery or vein level.

Optimal flushing agents for integrated optical and acoustic imaging systems

An increasing number of integrated optical and acoustic intravascular imaging systems have been developed and hold great promise for accurately diagnosing vulnerable plaques and guiding atherosclerosis treatment. However, in any intravascular environment, the vascular lumen is filled with blood, a high-scattering source for optical and high-frequency ultrasound signals. Blood must be flushed away to provide clearer images. To our knowledge, no research has been performed to find the ideal flushing agent for combined optical and acoustic imaging techniques. We selected three solutions as potential flushing agents for their image-enhancing effects: mannitol, dextran, and iohexol. Testing of these flushing agents was performed in a closed-loop circulation model and in vivo on rabbits. We found that a high concentration of dextran was the most useful for simultaneous intravascular ultrasound and optical coherence tomography imaging.

Study on the refractive index matching effect of ultrasound on optical clearing of bio-tissues based on the derivative total reflection method

In recent years, the tissue optical clearing (OC) technique in the biomedicine field has drawn lots of attention. Various physical and chemical methods have been introduced to improve the efficacy of OC. In this study, the effect of the combination of glycerol and ultrasound treatment on OC of in vitro porcine muscle tissues has been investigated. The refractive index (RI) matching mechanism of OC was directly observed based on the derivative total reflection method. A theoretical model was used to simulate the proportion of tissue fluid in the illuminated area. Moreover, the total transmittance spectra have been obtained by a spectrometer over the range from 450 nm to 700 nm. The administration of glycerol and ultrasound has led to an increase of the RI of background medium and a more RI matching environment was achieved. The experimental results support the validity of the ultrasound treatment for OC. The RI matching mechanism has been firstly quantitatively analyzed based on the derivative total reflection method.

Dynamic monitoring of optical clearing of skin using photoacoustic microscopy and ultrasonography

Tissue optical clearing technique has shown great potential for enhancing the imaging depth and contrast of optical imaging modalities. However, the mechanism of optical clearing is still in controversy. In this manuscript, we combined photoacoustic microscopy with ultrasonography to monitor the dermic changes induced by optical clearing agents at different immersion time points. The measured parameters were correlated with the optical clearing process, and could be used to assess the optical clearing effect. Both in vitro and in vivo results demonstrated that photoacoustic microscopy and ultrasonography can potentially be used as a powerful tool in screening optical clearing agents and exploring the mechanism of optical clearing.

Viscous optical clearing agent for in vivo optical imaging

By allowing more photons to reach deeper tissue, the optical clearing agent (OCA) has gained increasing attention in various optical imaging modalities. However, commonly used OCAs have high fluidity, limiting their applications in in vivo studies with oblique, uneven, or moving surfaces. In this work, we reported an OCA with high viscosity. We measured the properties of this viscous OCA, and tested its successful performances in the imaging of a living animal’s skin with two optical imaging modalities: photoacoustic microscopy and optical coherence tomography. Our results demonstrated that the viscous OCA has a great potential in the study of different turbid tissues using various optical imaging modalities.

Circulating Tumor Cell Detection and Capture by Photoacoustic Flow Cytometry in Vivo and ex Vivo

Despite progress in detecting circulating tumor cells (CTCs), existing assays still have low sensitivity (1-10 CTC/mL) due to the small volume of blood samples (5-10 mL). Consequently, they can miss up to 103-104 CTCs, resulting in the development of barely treatable metastasis. Here we analyze a new concept of in vivo CTC detection with enhanced sensitivity (up to 102-103 times) by the examination of the entire blood volume in vivo (5 L in adults). We focus on in vivo photoacoustic (PA) flow cytometry (PAFC) of CTCs using label-free or targeted detection, photoswitchable nanoparticles with ultrasharp PA resonances, magnetic trapping with fiber-magnetic-PA probes, optical clearance, real-time spectral identification, nonlinear signal amplification, and the integration with PAFC in vitro. We demonstrate PAFC's capability to detect rare leukemia, squamous carcinoma, melanoma, and bulk and stem breast CTCs and its clusters in preclinical animal models in blood, lymph, bone, and cerebrospinal fluid, as well as the release of CTCs from primary tumors triggered by palpation, biopsy or surgery, increasing the risk of metastasis. CTC lifetime as a balance between intravasation and extravasation rates was in the range of 0.5-4 h depending on a CTC metastatic potential. We introduced theranostics of CTCs as an integration of nanobubble-enhanced PA diagnosis, photothermal therapy, and feedback through CTC counting. In vivo data were verified with in vitro PAFC demonstrating a higher sensitivity (1 CTC/40 mL) and throughput (up to 10 mL/min) than conventional assays. Further developments include detection of circulating cancer-associated microparticles, and super-rsesolution PAFC beyond the diffraction and spectral limits.