Assessing hyperthermia-induced vasodilation in human skin in vivo using optoacoustic mesoscopy

Machine Learning Analysis of Human Skin by Optoacoustic Mesoscopy for Automated Extraction of Psoriasis and Aging Biomarkers

Ultra-wideband raster-scan optoacoustic mesoscopy (RSOM) is a novel modality that has demonstrated unprecedented ability to visualize epidermal and dermal structures in-vivo. However, an automatic and quantitative analysis of three-dimensional RSOM datasets remains unexplored. In this work we present our framework: Deep Learning RSOM Analysis Pipeline (DeepRAP), to analyze and quantify morphological skin features recorded by RSOM and extract imaging biomarkers for disease characterization. DeepRAP uses a multi-network segmentation strategy based on convolutional neural networks with transfer learning. This strategy enabled the automatic recognition of skin layers and subsequent segmentation of dermal microvasculature with an accuracy equivalent to human assessment. DeepRAP was validated against manual segmentation on 25 psoriasis patients under treatment and our biomarker extraction was shown to characterize disease severity and progression well with a strong correlation to physician evaluation and histology. In a unique validation experiment, we applied DeepRAP in a time series sequence of occlusion-induced hyperemia from 10 healthy volunteers. We observe how the biomarkers decrease and recover during the occlusion and release process, demonstrating accurate performance and reproducibility of DeepRAP. Furthermore, we analyzed a cohort of 75 volunteers and defined a relationship between aging and microvascular features in-vivo. More precisely, this study revealed that fine microvascular features in the dermal layer have the strongest correlation to age. The ability of our newly developed framework to enable the rapid study of human skin morphology and microvasculature in-vivo promises to replace biopsy studies, increasing the translational potential of RSOM.

Hybrid Photoacoustic Ultrasound Imaging System for Cold-Induced Vasoconstriction and Vasodilation Monitoring

Lewis hunting reaction refers to the alternating cold-induced vasoconstriction and dilation in extremities, whose underlying mechanism is complex. While numerous studies reported this intriguing phenomenon by measuring cutaneous temperature fluctuation under cold exposure, few of them tracked peripheral vascular responses in real-time, lacking a non-invasive and quantitative imaging tool. To better monitor hunting reaction and diagnose relevant diseases, we developed a hybrid photoacoustic ultrasound (PAUS) tomography system to monitor finger vessels' dynamic response to cold, together with simultaneous temperature measurement. We also came out a standard workflow for image analysis with self-defined indices. In the small cohort observational study, vascular changes in the first cycle of hunting reaction were successfully captured by the image series and quantified. Time difference between vasodilation and temperature recovery was noticed and reported for the first time, thanks to the unique capability of the PAUS imaging system in real-time and continuous vascular monitoring. The developed imaging system and indices enabled more objective and quantitative monitoring of peripheral vascular activities, indicating its great potential in numerous clinical applications.

Opening a window to skin biomarkers for diabetes stage with optoacoustic mesoscopy

Being the largest and most accessible organ of the human body, the skin could offer a window to diabetes-related complications on the microvasculature. However, skin microvasculature is typically assessed by histological analysis, which is not suited for applications to large populations or longitudinal studies. We introduce ultra-wideband raster-scan optoacoustic mesoscopy (RSOM) for precise, non-invasive assessment of diabetes-related changes in the dermal microvasculature and skin micro-anatomy, resolved with unprecedented sensitivity and detail without the need for contrast agents. Providing unique imaging contrast, we explored a possible role for RSOM as an investigational tool in diabetes healthcare and offer the first comprehensive study investigating the relationship between different diabetes complications and microvascular features in vivo. We applied RSOM to scan the pretibial area of 95 participants with diabetes mellitus and 48 age-matched volunteers without diabetes, grouped according to disease complications, and extracted six label-free optoacoustic biomarkers of human skin, including dermal microvasculature density and epidermal parameters, based on a novel image-processing pipeline. We then correlated these biomarkers to disease severity and found statistically significant effects on microvasculature parameters as a function of diabetes complications. We discuss how label-free RSOM biomarkers can lead to a quantitative assessment of the systemic effects of diabetes and its complications, complementing the qualitative assessment allowed by current clinical metrics, possibly leading to a precise scoring system that captures the gradual evolution of the disease.

Raster-scanning optoacoustic mesoscopy biomarkers for atopic dermatitis skin lesions

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease worldwide. Its severity is assessed using scores that rely on visual observation of the affected body surface area, the morphology of the lesions and subjective symptoms, like pruritus or insomnia. Ideally, such scores should be complemented by objective and accurate measurements of disease severity to standardize disease scoring in routine care and clinical trials. Recently, it was shown that raster-scanning optoacoustic mesoscopy (RSOM) can provide detailed three-dimensional images of skin inflammation processes that capture the most relevant features of their pathology. Moreover, precise RSOM biomarkers of inflammation have been identified for psoriasis. However, the objectivity and validity of such biomarkers in repeated measurements have not yet been assessed for AD. Here, we report the results of a study on the repeatability of RSOM inflammation biomarkers in AD to estimate their precision. Optoacoustic imaging analysis revealed morphological inflammation biomarkers with precision well beyond standard clinical severity metrics. Our findings suggest that optoacoustic mesoscopy may be a good choice for quantitative evaluations of AD that are inaccessible by other methods. This could potentially enable the optimization of disease scoring and drug development.

Plasmodium sporozoite search strategy to locate hotspots of blood vessel invasion

Plasmodium sporozoites actively migrate in the dermis and enter blood vessels to infect the liver. Despite their importance for malaria infection, little is known about these cutaneous processes. We combine intravital imaging in a rodent malaria model and statistical methods to unveil the parasite strategy to reach the bloodstream. We determine that sporozoites display a high-motility mode with a superdiffusive Lévy-like pattern known to optimize the location of scarce targets. When encountering blood vessels, sporozoites frequently switch to a subdiffusive low-motility behavior associated with probing for intravasation hotspots, marked by the presence of pericytes. Hence, sporozoites present anomalous diffusive motility, alternating between superdiffusive tissue exploration and subdiffusive local vessel exploitation, thus optimizing the sequential tasks of seeking blood vessels and pericyte-associated sites of privileged intravasation.

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

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

Image Quality Improvement Techniques and Assessment Adequacy in Clinical Optoacoustic Imaging: A Systematic Review

Optoacoustic imaging relies on the detection of optically induced acoustic waves to offer new possibilities in morphological and functional imaging. As the modality matures towards clinical application, research efforts aim to address multifactorial limitations that negatively impact the resulting image quality. In an endeavor to obtain a clear view on the limitations and their effects, as well as the status of this progressive refinement process, we conduct an extensive search for optoacoustic image quality improvement approaches that have been evaluated with humans in vivo, thus focusing on clinically relevant outcomes. We query six databases (PubMed, Scopus, Web of Science, IEEE Xplore, ACM Digital Library, and Google Scholar) for articles published from 1 January 2010 to 31 October 2021, and identify 45 relevant research works through a systematic screening process. We review the identified approaches, describing their primary objectives, targeted limitations, and key technical implementation details. Moreover, considering comprehensive and objective quality assessment as an essential prerequisite for the adoption of such approaches in clinical practice, we subject 36 of the 45 papers to a further in-depth analysis of the reported quality evaluation procedures, and elicit a set of criteria with the intent to capture key evaluation aspects. Through a comparative criteria-wise rating process, we seek research efforts that exhibit excellence in quality assessment of their proposed methods, and discuss features that distinguish them from works with similar objectives. Additionally, informed by the rating results, we highlight areas with improvement potential, and extract recommendations for designing quality assessment pipelines capable of providing rich evidence.

Enabling the autofocus approach for parameter optimization in planar measurement geometry clinical optoacoustic imaging

In optoacoustic (photoacoustic) tomography, several parameters related to tissue and detector features are needed for image formation, but they may not be known a priori. An autofocus (AF) algorithm is generally used to estimate these parameters. However, the algorithm works iteratively and is therefore impractical for clinical imaging with planar geometry systems due to the long reconstruction times. We have developed a fast autofocus (FAF) algorithm for 3D optoacoustic systems with planar geometry. Such an algorithm exploits the symmetries of the planar geometry and a virtual source concept to reduce the dimensionality of the parameter estimation problem. The dimensionality reduction makes FAF much simpler computationally than the conventional AF algorithm. We show that the FAF algorithm required about 5 s to provide accurate estimates of the speed of sound in simulated data and experimental data obtained using an imaging system that is poised to enter the clinic. The applicability of FAF for estimating other image formation parameters is discussed. We expect the FAF algorithm to contribute decisively to the clinical use of optoacoustic tomography systems with planar geometry.

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

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

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

[Optoacoustic imaging-Applications and advancements of innovative imaging techniques]

Optoacoustic imaging (OAB) has developed steadily in recent years. By means of partly pulsed light, in a wide variety of wavelengths, different colour carriers (chromophores) are excited to form sound waves. These in turn are detected by the newly developed systems and converted into three-dimensional images by means of various algorithms. The technique is characterised by a good ratio between contrast and penetration depth and can create macro-, meso- and microscopic images due to its scalability. Optoacoustic macroscopy broadly irradiates the area to be examined with laser light. This can produce images with a high penetration depth, but only with a moderate resolution. Clinically interesting fields of application are for example the results of sentinel lymph nodes (SLNs) examined ex vivo using macroscopic optoacoustics. Due to the ability of OAB to visualise melanin, the detection rate of metastases was superior to previous methods, but not to histology. The ability to visualise dermal and epidermal structures, especially vessels, with good resolution makes optoacoustic mesoscopy useful in the examination of inflammatory skin diseases and could contribute to the verification of the success of therapy, e.g., with biologics for psoriasis vulgaris or atopic eczema (AE), in the future. Optoacoustic microscopy, which has so far been limited mainly to preclinical in vivo research, could be used in the future to detect even finer vascular structures and their changes. The clinical possibilities of OAB seem to be of great benefit and continue to be the subject of intensive research.

Optoacoustic imaging in endocrinology and metabolism

Imaging is an essential tool in research, diagnostics and the management of endocrine disorders. Ultrasonography, nuclear medicine techniques, MRI, CT and optical methods are already used for applications in endocrinology. Optoacoustic imaging, also termed photoacoustic imaging, is emerging as a method for visualizing endocrine physiology and disease at different scales of detail: microscopic, mesoscopic and macroscopic. Optoacoustic contrast arises from endogenous light absorbers, such as oxygenated and deoxygenated haemoglobin, lipids and water, or exogenous contrast agents, and reveals tissue vasculature, perfusion, oxygenation, metabolic activity and inflammation. The development of high-performance optoacoustic scanners for use in humans has given rise to a variety of clinical investigations, which complement the use of the technology in preclinical research. Here, we review key progress with optoacoustic imaging technology as it relates to applications in endocrinology; for example, to visualize thyroid morphology and function, and the microvasculature in diabetes mellitus or adipose tissue metabolism, with particular focus on multispectral optoacoustic tomography and raster-scan optoacoustic mesoscopy. We explain the merits of optoacoustic microscopy and focus on mid-infrared optoacoustic microscopy, which enables label-free imaging of metabolites in cells and tissues. We showcase current optoacoustic applications within endocrinology and discuss the potential of these technologies to advance research and clinical practice.

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.

In-vivo hemodynamic imaging of acute prenatal ethanol exposure in fetal brain by photoacoustic tomography

Prenatal ethanol exposure (PEE) can lead to structural and functional abnormalities in fetal brain. Although neural developmental deficits due to PEE have been recognized, the immediate effects of PEE on fetal brain vasculature and hemodynamics remain poorly understood. One of the major obstacles that preclude the rapid advancement of studies on fetal vascular dynamics is the limitation of the imaging techniques. Thus, a technique for noninvasive in-vivo imaging of fetal vasculature and hemodynamics is desirable. In this study, we explored the dynamic changes of the vessel dimeter, density and oxygen saturation in fetal brain after acute maternal ethanol exposure in the second-trimester equivalent murine model using a real-time photoacoustic tomography system we developed for imaging embryo of small animals. The results indicate a significant decrease in fetal brain vessel diameter, perfusion and oxygen saturation. This work demonstrated that PAT can provide high-resolution noninvasive imaging ability to monitor fetal vascular dynamics.

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

The monitoring of vascular-targeted therapies via magnetic resonance imaging, computed omography or ultrasound is limited by their insufficient spatial resolution. By taking advantage of the intrinsic optical properties of haemoglobin, here we show that raster-scanning optoacoustic mesoscopy (RSOM) provides high-resolution images of the tumour vasculature and of the surrounding tissue, and that the detection of a wide range of ultrasound bandwidths enables the distinction of vessels of differing size, allowing for detailed insights into vascular responses to vascular-targeted therapy. By using RSOM to examine the responses to vascular-targeted photodynamic therapy in mice with subcutaneous xenografts, we observed a significant and immediate occlusion of the tumour vessels, followed by haemorrhage within the tissue and the eventual collapse of the entire vasculature. By using dual-wavelength RSOM, which distinguishes oxyhaemoglobin from deoxyhaemoglobin, we observed an increase in oxygenation of the entire tumour volume immediately after the application of the therapy, and a second wave of oxygen reperfusion approximately 24 h thereafter. We also show that RSOM allows for the quantification of differences in neo-angiogenesis that predict treatment efficacy.

Percutaneous Nephrolithotomy with Different Temperature Irrigation and Effects on Surgical Complications and Anesthesiology Applications

OBJECTIVE

Percutaneous nephrolithotomy (PCNL) is a widely accepted and frequently performed operation for large kidney stones. However, there is not much information about the effects of irrigation fluid temperature as well as many other factors that affect success and complications during the operation. In this study, we aimed to investigate the surgical and anesthesiological effects of irrigation fluid used in body temperature and room temperature during and after PCNL.

MATERIAL AND METHODS

A total of 108 PCNL patients were performed between June 2016 and April 2018. The half of these patients (54) were performed with body temperature (37°C) irrigation fluid, hence known as body temperature group (BTG), and the other half with room temperature (22°C) irrigation fluid, called as room temperature group (RTG). For the study, we recorded the body temperature of the patients during and after the operation, the amount of irrigation fluid used, the size and location of the kidney stones, the duration of the operation, postoperative shivering time during the patient's wake-up period, pre- and postoperative hemoglobin value, additional blood requirements, postoperative analgesic requirements, and postoperative urinary tract infections.

RESULTS

The age of patients, gender distribution, height, weight, body mass index, stone size, and postoperative analgesic requirement showed no significant differences in two groups. The postoperative body heat was significantly higher in the BTG than the RTG. The duration of waking was significantly higher in the RTG than the BTG. The amount of hemorrhage was significantly less in the patients who were irrigated in the RTG.

CONCLUSION

The temperature of the irrigation fluid can affect many parameters in the PCNL. We recommend using irrigation in room temperature especially with patients having bleeding risks and irrigation fluid in body temperature especially with patients having anesthetic risks for easier waking process.

Optoacoustic mesoscopy analysis and quantitative estimation of specific imaging metrics in Fitzpatrick skin phototypes II to V

Raster Scanning Optoacoustic Mesoscopy (RSOM) is a novel optoacoustic imaging modality that offers non-invasive, label-free, high resolution (~7 μm axial, ~30 μm lateral) imaging up to 1 to 2 mm below the skin, providing novel quantitative insights into skin pathophysiology. As the RSOM image contrast mechanism is based on light absorption, it is expected that the amount of melanin present in the skin will affect RSOM images. However, the effect of skin tone in the performance of RSOM has not been addressed so far. Herein, we present the efficiency of RSOM for in vivo skin imaging of human subjects with Fitzpatrick (FP) skin types between II to V. RSOM images acquired from the volar forearms of the subjects were used to derive metrics used in RSOM studies, such as total blood volume, vessel diameter and melanin signal intensity. Our study shows that the melanin signal intensity derived from the RSOM images exhibited an excellent correlation with that obtained from a clinical colorimeter for the subjects of varying FP skin types. We could successfully estimate the vessel diameter at different depths of the dermis. Furthermore, our study shows that there is a need to compensate for total blood volume calculated for subjects with higher FP skin types due to the lower signal-to-noise ratio in dermis, owing to strong absorption of light by melanin. This study sheds light into how RSOM can be used for studying various skin conditions in populations with different skin phenotypes.

Optical features of human skin revealed by optoacoustic mesoscopy in the visible and short-wave infrared regions

Detailed assessment of skin conditions or the efficacy of skin treatments could greatly benefit from noninvasively assessing the distribution of cutaneous and subcutaneous structures and biomolecules. We considered ultrawideband raster scan optoacoustic mesoscopy with an extended wavelength range from visible to short-wave infrared and observed previously unseen high-resolution images of lipids colocalized with water, melanin, and hemoglobin distribution in human skin. Based on this contrast, the technique resolves subcutaneous fat, the pilosebaceous unit with complete hair strand and bulb, dermal microvasculature, and epidermal structures. We further visualize melanoidins that form via the Maillard reaction in the ultrathin stratum corneum layer, analyze their absorption spectrum, and separate them from the melanin layer. The suggested method may allow novel interrogation of skin conditions, possibly impacting diagnostics and medical and cosmetic treatments.

Fully automated identification of skin morphology in raster-scan optoacoustic mesoscopy using artificial intelligence

PURPOSE

Identification of morphological characteristics of skin lesions is of vital importance in diagnosing diseases with dermatological manifestations. This task is often performed manually or in an automated way based on intensity level. Recently, ultra-broadband raster-scan optoacoustic mesoscopy (UWB-RSOM) was developed to offer unique cross-sectional optical imaging of the skin. A machine learning (ML) approach is proposed here to enable, for the first time, automated identification of skin layers in UWB-RSOM data.

MATERIALS AND METHODS

The proposed method, termed SkinSeg, was applied to coronal UWB-RSOM images obtained from 12 human participants. SkinSeg is a multi-step methodology that integrates data processing and transformation, feature extraction, feature selection, and classification. Various image features and learning models were tested for their suitability at discriminating skin layers including traditional machine learning along with more advanced deep learning algorithms. An support vector machines-based postprocessing approach was finally applied to further improve the classification outputs.

RESULTS

Random forest proved to be the most effective technique, achieving mean classification accuracy of 86.89% evaluated based on a repeated leave-one-out strategy. Insights about the features extracted and their effect on classification accuracy are provided. The highest accuracy was achieved using a small group of four features and remained at the same level or was even slightly decreased when more features were included. Convolutional neural networks provided also promising results at a level of approximately 85%. The application of the proposed postprocessing technique was proved to be effective in terms of both testing accuracy and three-dimensional visualization of classification maps.

CONCLUSIONS

SkinSeg demonstrated unique potential in identifying skin layers. The proposed method may facilitate clinical evaluation, monitoring, and diagnosis of diseases linked to skin inflammation, diabetes, and skin cancer.

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.

Photoacoustic computed tomography with lens-free focused fiber-laser ultrasound sensor

Optical detection of ultrasound is attractive to photoacoustic imaging due to its high sensitivity per unit area, broad bandwidth, and electromagnetic immunity. To enhance the sensitivity, previous optical transducers commonly necessitate bulk acoustic lenses to achieve focused ultrasound detection. Here, we proposed and demonstrated a novel lens-free focused optical ultrasound sensor by mechanically bending a flexible fiber laser. At a curvature radius of 30 mm, the curved fiber laser well conformed to the spherical wavefront of ultrasound exhibiting ~5 times higher sensitivity compared with the straight one. The focused fiber laser ultrasound sensor (FUS) presented a minimum detectable pressure of ~36 Pa with a working distance equal to its curvature radius. The sensor was applied to circular scanning photoacoustic computed tomography (PACT), which showed a ~70 μm in-plane resolution and a ~500 μm elevational resolution. In vivo imaging of a zebrafish and mouse brain shows the potential of this focused FUS for photoacoustic imaging in biological/medical studies.

Non-invasive imaging in dermatology and the unique potential of raster-scan optoacoustic mesoscopy

In recent years, several non‐invasive imaging methods have been introduced to facilitate diagnostics and therapy monitoring in dermatology. The microscopic imaging methods are restricted in their penetration depth, while the mesoscopic methods probe deeper but provide only morphological, not functional, information. ‘Raster‐scan optoacoustic mesoscopy’ (RSOM), an emerging new imaging technique, combines deep penetration with contrast based on light absorption, which provides morphological, molecular and functional information. Here, we compare the capabilities and limitations of currently available dermatological imaging methods and highlight the principles and unique abilities of RSOM. We illustrate the clinical potential of RSOM, in particular for non‐invasive diagnosis and monitoring of inflammatory and oncological skin diseases.

Ultrasmall hybrid protein–copper sulfide nanoparticles for targeted photoacoustic imaging of orthotopic hepatocellular carcinoma with a high signal-to-noise ratio

A schematic illustration of CuS@BSA-RGD nanoparticle synthesis and the application of photoacoustic imaging in an orthotopic HCC model.