Panoramic volumetric clinical handheld photoacoustic and ultrasound imaging

In vivo 3D photoacoustic and ultrasound analysis of hypopigmented skin lesions: A pilot study

Vitiligo needs early identification for proper intervention. Current adjunct diagnostic methods rely mostly on subjective visual inspection. Thus, identification of early or atypical vitiligo lesions among other hypopigmentation disorders may pose challenges. To overcome this, we investigate the feasibility of a three-dimensional (3D) photoacoustic (PA) and ultrasound (US) imaging technique as a new adjuvant analytic tool providing quantitative characterization of hypopigmentation features. This cross-sectional study was conducted at Seoul St. Mary's Hospital (Seoul, Republic of Korea) between August 2022 and January 2024. Lesions diagnosed vitiligo or IGH in locations that could safely be irradiated with laser were analyzed with 3D PA/US imaging along with the conventional diagnostic methods. A total of 53 lesions consisted of 36 vitiligo lesions and 17 IGH lesions from 39 participants with confirmed diagnosis were analyzed. The PA amplitude greatly differed between normal skin and hypopigmentation lesions, and the mean PA amplitudes of vitiligo lesions were slightly higher than that of IGH [mean (standard deviation, SD): vitiligo: 0.117 (0.043); IGH: 0.135 (0.028)]. The local SD of the PA amplitude were higher in IGH than in vitiligo lesions [vitiligo: 0.043 (0.018); IGH: 0.067 (0.017)]. The mean PA slope across the lesion boundary was significantly higher in IGH than in vitiligo [vitiligo: 0.173 (0.061); IGH: 0.342 (0.099)], whereas the PA peak depth was deeper in vitiligo than in IGH [vitiligo: 0.568 (0.262); IGH: 0.266 (0.116)]. Unlike conventional qualitative methods, 3D PA/US imaging can non-invasively provide quantitative metrics which might aid in the differentiation of vitiligo from IGH lesions.

A clinical feasibility study of a photoacoustic finder for sentinel lymph node biopsy in breast cancer patients: A prospective cross-sectional study

The sentinel lymph node (SLNb) is generally performed using radioisotopes, blue dyes, or both to improve false negative rate. However, ionizing radiation is involved in a gamma probe with radioisotopes and the blue dye detection relies on native visual inspection by an operator. To overcome these limitations, we developed the photoacoustic finder (PAF), a highly sensitive, non-radioactive detector that uses only blue dye and a photoacoustic signal to detect SLNs. A total of 121 patients with breast cancer were enrolled, and 375 lymph nodes were excised using conventional SLNb. The PAF was used to measure the signal from the excised lymph nodes. We compared the SLN detection rates of each method (gamma probe, visual inspection, and PAF) and conducted a non-inferiority test. The PAF detected 87 % of SLNs, comparable to the gamma probe (85 %) and superior to visual inspection (73 %). Non-inferiority tests confirmed PAF's performance was not inferior to visual inspection (p < 0.001) or the gamma probe (p < 0.015). Using the dual-modal method (gamma probe + visual inspection) as the gold standard, PAF showed a sensitivity of 0.81 and specificity of 0.63. This study demonstrates that PAF, using only blue dye, offers a non-inferior alternative to the standard dual-modal SLN detection method with radioactive materials, opening new avenues for radiation-free SLNb in the future.

Enhanced clinical photoacoustic vascular imaging through a skin localization network and adaptive weighting

Photoacoustic tomography (PAT) is an emerging imaging modality with widespread applications in both preclinical and clinical studies. Despite its promising capabilities to provide high-resolution images, the visualization of vessels might be hampered by skin signals and attenuation in tissues. In this study, we have introduced a framework to retrieve deep vessels. It combines a deep learning network to segment skin layers and an adaptive weighting algorithm to compensate for attenuation. Evaluation of enhancement using vessel occupancy metrics and signal-to-noise ratio (SNR) demonstrates that the proposed method significantly recovers deep vessels across various body positions and skin tones. These findings indicate the method's potential to enhance quantitative analysis in preclinical and clinical photoacoustic research.

Collagen fibers quantification for liver fibrosis assessment using linear dichroism photoacoustic microscopy

Liver fibrosis represents a progressive pathological condition that can culminate in severe hepatic dysfunction, potentially advancing to cirrhosis and liver cancer. The extent of liver fibrosis is intrinsically associated with the quantity of collagen fibers. Although liver biopsy and ultrasound imaging are standard diagnostic tools, their application is constrained by risks of significant complications and variability in different investigators, respectively. In this study, we utilized linear dichroism photoacoustic microscopy (LDPAM) to visualize and quantify collagen fibers, which exhibit specific absorption of polarized light, subsequently calculating a collagen fibers degree of dichroism (CDOD) score. We obtained high-resolution images of liver structures, with an emphasis on collagen fibers within the hepatic tissue. Using the CDOD score, we categorized liver fibrosis into three distinct stages: normal, early, and advanced. For validation purposes, collagen fibers were visualized with Sirius-red staining and quantitatively assessed through the collagen proportional area (CPA) score. Our results demonstrated a significant correlation between the CDOD and CPA scores, with a Pearson coefficient of 0.95. This approach presents a promising and non-invasive method for assessing liver fibrosis by quantifying collagen fibers.

Non-Invasive Photoacoustic Cerebrovascular Monitoring of Early-Stage Ischemic Strokes In Vivo

Early-stage stroke monitoring enables timely intervention that is crucial to minimizing neuronal damage and increasing the extent of recovery. By monitoring collateral circulation and neovascularization after ischemic stroke, the natural recovery process can be better understood, optimize further treatment strategies, and improve the prognosis. Photoacoustic computed tomography (PACT), a non-invasive imaging modality that captures multiparametric high-resolution images of vessel structures, is well suited for evaluating cerebrovascular structures and their function. Here 3D multiparametric transcranial PACT is implemented to monitor the early stage of a photothrombotic (PT)-stroke model in living rats. New vessels in the PT-induced region are successfully observed using PACT, and these observations are confirmed by histology. Then, using multiparametric PACT, it is found that the SO2 in the ischemic area decreases while the SO2 in newly formed vessels increases, and the SO2 in the PT region also recovers. These findings demonstrate PACT's remarkable ability to image and monitor cerebrovascular morphologic and physiological changes. They highlight the usefulness of whole-brain PACT as a potentially powerful tool for early diagnosis and therapeutic decision-making in treating ischemic stroke.

Quantitative volumetric photoacoustic assessment of vasoconstriction by topical corticosteroid application in mice skin

Topical corticosteroids manage inflammatory skin conditions via their action on the immune system. An effect of application of corticosteroids to the skin is skin blanching caused by peripheral vasoconstriction. This has been used to characterize, in some cases relative potency and also as a way to compare skin penetration. Chromameters have been used to assess skin blanching-the outcome of vasoconstriction caused by topical corticosteroids-but do not directly measure vasoconstriction. Here, we demonstrate quantitative volumetric photoacoustic microscopy (PAM) as a tool for directly assessing the vasoconstriction followed by topical corticosteroid application, noninvasively visualizing skin vasculature without any exogeneous contrast agent. We photoacoustically differentiated the vasoconstrictive ability of four topical corticosteroids in small animals through multiparametric analyses, offering detailed 3D insights into vasoconstrictive mechanisms across different skin depths. Our findings highlight the potential of PAM as a noninvasive tool for measurement of comparative vasoconstriction with potential for clinical, pharmaceutical, and bioequivalence applications.

Survey on portable sensing technologies for the radial artery characterization

The radial artery, one of the terminal branches of the forearm, is utilized for vascular access and in various non-invasive measurement method, providing crucial medical insights. Various sensor technologies have been developed, each suited to specific characterization requirements. The work presented in this paper is based on a systematic literature review of the main publications relating to this topic. Analysis of the forearm vascular system complex array of anatomical structures shows that the radial artery can be characterized by its size, position, elasticity, tissue evaluation, blood flow and blood composition. The survey of medical procedures for patient monitoring, diagnosis and pre-operative validation shows the use of measures for pulse wave, blood pressure, heart rate, skin temperature, tissue response,…By exploring sensor technologies used for artery characterization, we produce a synthesis of measurement principles, measured phenomena and measurement accuracy for capacitive, piezoresistive, bioimpedance, thermography, fiber optic based, piezoelectric and photoacoustic sensors. A comparative study is conducted for sensor technologies by considering the metrics of the information to be collected and the associated accuracy as well as the portability, the complexity of the processing, the cost and the mode of contact with the arm. Finally, a comprehensive framework is proposed to facilitate informed decisions in the development of medical devices tailored to specific characterization needs.

X-ray free-electron laser induced acoustic microscopy (XFELAM)

The X-ray free-electron laser (XFEL) has remarkably advanced X-ray imaging technology and enabled important scientific achievements. The XFEL's extremely high power, short pulse width, low emittance, and high coherence make possible such diverse imaging techniques as absorption/emission spectroscopy, diffraction imaging, and scattering imaging. Here, we demonstrate a novel XFEL-based imaging modality that uses the X-ray induced acoustic (XA) effect, which we call X-ray free-electron laser induced acoustic microscopy (XFELAM). Initially, we verified the XA effect by detecting XA signals from various materials, then we validated the experimental results with simulation outcomes. Next, in resolution experiments, we successfully imaged a patterned tungsten target with drilled various-sized circles at a spatial resolution of 7.8 ± 5.1 µm, which is the first micron-scale resolution achieved by XA imaging. Our results suggest that the novel XFELAM can expand the usability of XFEL in various areas of fundamental scientific research.

Video-rate endocavity photoacoustic/harmonic ultrasound imaging with miniaturized light delivery

Significance

Endocavity ultrasound (US) imaging is a frequently employed diagnostic technique in gynecology and urology for the assessment of male and female genital diseases that present challenges for conventional transabdominal imaging. The integration of photoacoustic (PA) imaging with clinical US imaging has displayed promising outcomes in clinical research. Nonetheless, its application has been constrained due to size limitations, restricting it to spatially confined locations such as vaginal or rectal canals.

Aim

This study presents the development of a video-rate (20 Hz) endocavity PA/harmonic US imaging (EPAUSI) system.

Approach

The approach incorporates a commercially available endocavity US probe with a miniaturized laser delivery unit, comprised of a single large-core fiber and a line beamshaping engineered diffuser. The system facilitates real-time image display and subsequent processing, including angular energy density correction and spectral unmixing, in offline mode.

Results

The spatial resolutions of the concurrently acquired PA and harmonic US images were measured at 318    μ m and 291    μ m in the radial direction, respectively, and 1.22 deg and 1.50 deg in the angular direction, respectively. Furthermore, the system demonstrated its capability in multispectral PA imaging by successfully distinguishing two clinical dyes in a tissue-mimicking phantom. Its rapid temporal resolution enabled the capture of kinetic dye perfusion into an ex vivo porcine ovary through the depth of porcine uterine tissue. EPAUSI proved its clinical viability by detecting pulsating hemodynamics in the male rat's prostate in vivo and accurately classifying human blood vessels into arteries and veins based on sO 2 measurements.

Conclusions

Our proposed EPAUSI system holds the potential to unveil previously overlooked indicators of vascular alterations in genital cancers or endometriosis, addressing pressing requirements in the fields of gynecology and urology.

Mini review of photoacoustic clinical imaging: a noninvasive tool for disease diagnosis and treatment evaluation

Significance

Photoacoustic (PA) imaging is an imaging modality that integrates anatomical, functional, metabolic, and histologic insights. It has been a hot topic of medical research and draws extensive attention.

Aim

This review aims to explore the applications of PA clinical imaging in human diseases, highlighting recent advancements.

Approach

A systemic survey of the literature concerning the clinical utility of PA imaging was conducted, with a particular focus on its application in tumors, autoimmune diseases, inflammatory conditions, and endocrine disorders.

Results

PA imaging is emerging as a valuable tool for human disease investigation. Information provided by PA imaging can be used for diagnosis, grading, and prognosis in multiple types of tumors including breast tumors, ovarian neoplasms, thyroid nodules, and cutaneous malignancies. PA imaging facilitates the monitoring of disease activity in autoimmune and inflammatory diseases such as rheumatoid arthritis, systemic sclerosis, arteritis, and inflammatory bowel disease by capturing dynamic functional alterations. Furthermore, its unique capability of visualizing vascular structure and oxygenation levels aids in assessing diabetes mellitus comorbidities and thyroid function.

Conclusions

Despite extant challenges, PA imaging offers a promising noninvasive tool for precision disease diagnosis, long-term evaluation, and prognosis anticipation, making it a potentially significant imaging modality for clinical practice.

Review of Three-Dimensional Handheld Photoacoustic and Ultrasound Imaging Systems and Their Applications

Photoacoustic (PA) imaging is a non-invasive biomedical imaging technique that combines the benefits of optics and acoustics to provide high-resolution structural and functional information. This review highlights the emergence of three-dimensional handheld PA imaging systems as a promising approach for various biomedical applications. These systems are classified into four techniques: direct imaging with 2D ultrasound (US) arrays, mechanical-scanning-based imaging with 1D US arrays, mirror-scanning-based imaging, and freehand-scanning-based imaging. A comprehensive overview of recent research in each imaging technique is provided, and potential solutions for system limitations are discussed. This review will serve as a valuable resource for researchers and practitioners interested in advancements and opportunities in three-dimensional handheld PA imaging technology.

Dual-wavelength UV-visible metalens for multispectral photoacoustic microscopy: A simulation study

Photoacoustic microscopy is advancing with research on utilizing ultraviolet and visible light. Dual-wavelength approaches are sought for observing DNA/RNA- and vascular-related disorders. However, the availability of high numerical aperture lenses covering both ultraviolet and visible wavelengths is severely limited due to challenges such as chromatic aberration in the optics. Herein, we present a groundbreaking proposal as a pioneering simulation study for incorporating multilayer metalenses into ultraviolet-visible photoacoustic microscopy. The proposed metalens has a thickness of 1.4 µm and high numerical aperture of 0.8. By arranging cylindrical hafnium oxide nanopillars, we design an achromatic transmissive lens for 266 and 532 nm wavelengths. The metalens achieves a diffraction-limited focal spot, surpassing commercially available objective lenses. Through three-dimensional photoacoustic simulation, we demonstrate high-resolution imaging with superior endogenous contrast of targets with ultraviolet and visible optical absorption bands. This metalens will open new possibilities for downsized multispectral photoacoustic microscopy in clinical and preclinical applications.