Photoacoustic Microscopy Research Articles

Acoustic Resolution Photoacoustic Microscopy Imaging Enhancement: Integration of Group Sparsity with Deep Denoiser Prior

Acoustic Resolution Photoacoustic Microscopy Imaging Enhancement: Integration of Group Sparsity with Deep Denoiser Prior

Structure and Oxygen Saturation Recovery of Sparse Photoacoustic Microscopy Images by Deep Learning

Structure and Oxygen Saturation Recovery of Sparse Photoacoustic Microscopy Images by Deep Learning

Optical-resolution parallel ultraviolet photoacoustic microscopy for slide-free histology.

Intraoperative imaging of slide-free specimens is crucial for oncology surgeries, allowing surgeons to quickly identify tumor margins for precise surgical guidance. While high-resolution ultraviolet photoacoustic microscopy has been demonstrated for slide-free histology, the imaging speed is insufficient, due to the low laser repetition rate and the limited depth of field. To address these challenges, we present parallel ultraviolet photoacoustic microscopy (PUV-PAM) with simultaneous scanning of eight optical foci to acquire histology-like images of slide-free fresh specimens, improving the ultraviolet PAM imaging speed limited by low laser repetition rates. The PUV-PAM has achieved an imaging speed of 0.4 square millimeters per second (i.e., 4.2 minutes per square centimeter) at 1.3-micrometer resolution using a 50-kilohertz laser. In addition, we demonstrated the PUV-PAM with eight needle-shaped beams for an extended depth of field, allowing fast imaging of slide-free tissues with irregular surfaces. We believe that the PUV-PAM approach will enable rapid intraoperative photoacoustic histology and provide prospects for ultrafast optical-resolution PAM.

Adaptively spatial PSF removal enables contrast enhancement for multi-layer image fusion in photoacoustic microscopy.

Optical-resolution photoacoustic microscopy enables cellular-level biological imaging in deep tissues. However, acquiring high-quality spatial images without knowing the point spread function (PSF) at multiple depths or physically improving system performance is challenging. We propose an adaptive multi-layer photoacoustic image fusion (AMPIF) approach based on blind deconvolution and registration. Our findings indicate that the AMPIF method rapidly achieves optimized multi-layer focused fused images with superior resolution and contrast without relying on prior knowledge of the PSF. This method holds significant potential for fast imaging of living biological tissues with enhanced contrast at multiple imaging depths.

Enhanced imaging depth in optical coherence tomography and photoacoustic microscopy enabled by absorbing dye molecules

Enhanced imaging depth in optical coherence tomography and photoacoustic microscopy enabled by absorbing dye molecules

Multitask learning-powered large-volume, rapid photoacoustic microscopy with non-diffracting beams excitation and sparse sampling

Multitask learning-powered large-volume, rapid photoacoustic microscopy with non-diffracting beams excitation and sparse sampling

Photoacoustic Microscopy Offers a New Perspective on Imaging of Vascular Anomalies: A Case Series of Venous Malformations

Objectives: Vascular malformations are mostly benign but can potentially be life-threatening or function-threatening when involving vital structures or when associated with overgrowth syndromes. Yet, for these lesions that are predominantly cutaneous, diagnostic techniques like ultrasonography and magnetic resonance imaging may be inadequate in the characterization of these superficial lesions; leaving the alternative of invasive tissue biopsies. Methods: We explore an emerging imaging modality via the photoacoustic microscope, which relies on the optical properties of tissues—allowing the detection of hemoglobin, water, lipids, and other light-absorbing chromophores, resulting in greater contrast and spatial resolution than conventional ultrasonography. We detail a case series of 8 pediatric patients with venous malformations who presented at the Vascular Anomalies Clinic in KK Women’s & Children’s Hospital. The photoacoustic microscope device was applied to lesional and control skin in each patient, with measurements taken twice for each site. Results: Despite the small sample size, there was discernible visual and quantitative difference in vessel caliber and length between lesional and control skin—the majority of venous malformations had vessels with larger diameters and lengths than control vessels. Of sampled vessels, the diameter of vessels was larger in the lesional sample in 85.7% with a mean difference of +10.4 μm (P = .02); whereas 83.3% of studied vessels had longer vessel lengths in the lesional sample with a mean difference of +81.3 μm (P = .20). Conclusion: This descriptive case series serves as a pilot exploratory study to investigate vascular parameters (ie, vessel length and diameter) of venous malformations with an alternative noninvasive imaging tool like photoacoustic imaging, which provides higher resolution visualization and characterization of vessel architecture in superficial vascular anomalies. Subsequent studies building on this preliminary study data may be performed to compare venous malformations to other vascular anomalies. Future applications include the development of diagnostic algorithms for various vascular lesions to aid in rapid bedside diagnosis, visualization of the effects of treatment in real-time, and defining prognostic markers to determine response to treatment.

Resolution Enhancement Strategies in Photoacoustic Microscopy: A Comprehensive Review.

Photoacoustic imaging has emerged as a promising modality for medical imaging since its introduction. Photoacoustic microscopy (PAM), which is based on the photoacoustic effect, combines the advantages of both optical and acoustic imaging modalities. PAM facilitates high-sensitivity, high-resolution, non-contact, and non-invasive imaging by employing optical absorption as its primary contrast mechanism. The ability of PAM to specifically image parameters such as blood oxygenation and melanin content makes it a valuable addition to the suite of modern biomedical imaging techniques. This review aims to provide a comprehensive overview of the diverse technical approaches and methods employed by researchers to enhance the resolution of photoacoustic microscopy. Firstly, the fundamental principles of the photoacoustic effect and photoacoustic imaging will be presented. Subsequently, resolution enhancement methods for both acoustic-resolution photoacoustic microscopy (AR-PAM) and optical-resolution photoacoustic microscopy (OR-PAM) will be discussed independently. Finally, the aforementioned resolution enhancement methods for photoacoustic microscopy will be critically evaluated, and the current challenges and future prospects of this technology will be summarized.

Mid-infrared photoacoustic brain imaging enabled by cascaded gas-filled hollow-core fiber lasers.

Extending the photoacoustic microscopy (PAM) into the mid-infrared (MIR) molecular fingerprint region constitutes a promising route toward label-free imaging of biological molecular structures. Realizing this objective requires a high-energy nanosecond MIR laser source. However, existing MIR laser technologies are limited to either low pulse energy or free-space structure that is sensitive to environmental conditions. Fiber lasers are promising technologies for PAM for their potential to offer both high pulse energy and robust performance, which however have not yet been used for PAM because it is still at the infant research stage. We aim to employ the emerging gas-filled anti-resonant hollow-core fiber (ARHCF) laser technology for MIR-PAM for the purpose of imaging myelin-rich regions in a mouse brain. This laser source is developed with a high-pulse-energy nanosecond laser at , targeting the main absorption band of myelin sheaths, the primary chemical component of axons in the central nervous system. The laser mechanism relies on two-order gas-induced vibrational stimulated Raman scattering for non-linear wavelength conversion, starting from a 1060-nm pump laser to through the two-stage gas-filled ARHCFs. The developed fiber Raman laser was used for the first time for MIR-PAM of mouse brain regions containing structures rich in myelin. The high peak power of and robust performance of the generated MIR Raman pulse addressed the challenge faced by the commonly used MIR lasers. We pioneered the potential use of high-energy and nanosecond gas-filled ARHCF laser source to MIR-PAM, with a first attempt to report this kind of fiber laser source for PAM of lipid-rich myelin regions in a mouse brain. We also open up possibilities for expanding into a versatile multiwavelength laser source covering multiple biomarkers and being employed to image other materials such as plastics.

Large depth-of-field ultraviolet-visible photoacoustic histologic and microvascular imaging in vivo

Photoacoustic microscopy (PAM) can image diverse biological microstructures by harnessing characteristic optical absorption spectra of intrinsic nonfluorescent biomolecules. We incorporate ultraviolet (UV) and visible pulsed lasers into a PAM to develop an UV-visible PAM for label-free histologic and microvascular imaging, where the cell nuclei and blood vessels are specifically captured at high contrast relying on strong optical absorption of DNA/RNA and hemoglobin at 266 and 532 nm wavelengths, respectively. Moreover, two diffractive optical elements operating at UV and visible spectra are designed for engineering the excitation beams, significantly enlarging depths of field (DOFs > 200 μm). The UV-visible PAM demonstrates combined capabilities of dual imaging contrast, elongated DOFs, and micrometer-scale lateral resolution for delineating the spatial microarchitectures of both cell nuclei and blood vessels that are at different depth locations in the biological specimens with uneven surfaces. Longitudinal monitoring of the trauma is performed in mouse ear in vivo. Potentially, our UV-visible PAM could offer comprehensive histologic and microvascular information in a broad range of biomedical studies.

3-D Visualization of Atlantic salmon skin through Ultrasound and Photoacoustic Microscopy.

Three-dimensional photoacoustic imaging (PAM) has emerged as a promising technique for non-invasive label-free visualization and characterization of biological tissues with high spatial resolution and functional contrast. The application of PAM and ultrasound as a microscopy technique of study for Atlantic salmon skin is presented here. A custom ultrasound and photoacoustic experimental setup was used for conducting this experiment with a sample preparation method where the salmon skin is embedded in agarose and lifted from the bottom of the petridish. The results of C-scan, B-scan, and overlayed images of ultrasound and photoacoustic are presented. The results are then analyzed for understanding the pigment map and its relation to salmon behavior to external stimuli. The photoacoustic images are compared with the optical images and analyzed further. A custom colormap and alpha map is designed and the matrices responsible for PAM and ultrasound are inserted together to overlay the ultrasound image and PAM image on top of each other. In this study, we propose an approach that combines scanning acoustic microscopy (SAM) images with PAM images for providing a comprehensive understanding of the salmon skin tissue. Overlaying acoustic and photoacoustic images enabled unique visualization of tissue morphology, with respect to identification of structural features in the context of their pigment distribution.

Histological and photoacoustic evaluation of rectal cancer after neoadjuvant therapy using microvascular density.

As non-operative management of rectal cancer proliferates, re-staging and surveillance methods are critical in selecting appropriate patients for organ preservation versus proctectomy. In previous work, the authors have shown that transrectal acoustic resolution photoacoustic microscopy (ARPAM) co-registered with ultrasound can differentiate residual cancer from complete tumoural response to neoadjuvant therapy. We hypothesize that these findings are due to changes in microvascular density (MVD). Patients with rectal adenocarcinoma who underwent neoadjuvant therapy, transrectal photoacoustic imaging and resection were included. We first compared immunohistochemical staining with erythroblast transformation-specific-related gene (ERG) immunostain to standard CD31 to confirm adequate identification of endothelium. Tissue sections from identical blocks were stained with CD31 and ERG, and then a correlation was calculated between manually labelled CD31-stained vessels and ERG nuclei density. Second, representative tissue blocks from responders, partial responders and non-responders were stained with ERG. ERG nuclei density was quantified as a proxy for MVD. CD31 MVD and ERG nuclei density were strongly correlated (R2 = 0.87; P < 0.01). In the tumour bed of patients after neoadjuvant therapy, MVD of complete responders (599 nuclei/mm2; 95% CI 434-764) is significantly higher (P < 0.01) than that of partial responders (185 nuclei/mm2; 95% CI 64-306) and non-responders (117 nuclei/mm2; 95% CI 42-192). No significant difference was found between the partial responders and non-responders (P = 0.60). Microvascular density appears highest in cases of complete tumour response to neoadjuvant therapy, similar to normal rectal tissue. The histological microvascular patterns seen in treated tissue may explain the imaging patterns seen in photoacoustic microscopy.

Multimodal photoacoustic microscopy and optical coherence tomography ocular biomarker imaging in Alzheimer's disease in mice.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by amyloid beta (Aβ)-containing extracellular plaques and tau-containing intracellular neurofibrillary tangles. Reliable and more accessible biomarkers along with associated imaging methods are essential for early diagnosis and to develop effective therapeutic interventions. Described here is an integrated photoacoustic microscopy (PAM) and optical coherence tomography (OCT) dual-modality imaging system for multiple ocular biomarker imaging in an AD mouse model. Anti-Aβ-conjugated Au nanochains (AuNCs) were engineered and administered to the mice to provide molecular contrast of Aβ. The retinal vasculature structure and Aβ deposition in AD mice and wild-type (WT) mice were imaged simultaneously by dual-wavelength PAM. OCT distinguished significant differences in retinal layer thickness between AD and WT animals. With the unique ability of imaging the multiple ocular biomarkers via a coaxial multimodality imaging system, the proposed system provides a new tool for investigating the progression of AD in animal models, which could contribute to preclinical studies of AD.

Miniaturized photoacoustic microscope for multi-segmental spinal cord imaging in freely moving mice.

Long-term and non-narcotic hemodynamic imaging is indispensable for observing factual physiological information of the spinal cord. Unfortunately, achieving label-free, high-resolution, and widefield spinal cord imaging for mice under freely moving conditions is challenging. In this study, we developed a miniaturized photoacoustic microscope along with a corresponding photoacoustic spinal window to realize high-resolution, multi-segmental hemodynamic imaging of the spinal cord for freely moving mice. The microscope has an outer size of 32 mm × 23 mm × 10 mm, a weight of 5.8 g, and a 4.4 µm lateral resolution within an effective field of view (FOV) of 2.6 mm × 1.8 mm. To eliminate the off-focus phenomena during spinal imaging, the microscope is equipped with a miniature motor to adapt the focal plane. Besides, the microscope is slidable along a customized rail on the window to expand the FOV. We evaluated the stability of the microscope and analyzed vascular images of the spinal cord under various physiological states. The results suggest that the microscope is capable of performing stable, multi-segmental spinal cord imaging in freely moving mice, offering new insights into spinal cord hemodynamics and neurovascular coupling research.

Wavelength‐switchable synchronously pumped Raman fiber laser near 1.7 µm for multispectral photoacoustic microscopy

Wavelength‐switchable synchronously pumped Raman fiber laser near 1.7 µm for multispectral photoacoustic microscopy

Unveiling placental development in circadian rhythm-disrupted mice: A photo-acoustic imaging study on unstained tissue

IntroductionCircadian rhythm disruption has garnered significant attention for its adverse effects on human health, particularly in reproductive medicine and fetal well-being. Assessing pregnancy health often relies on diagnostic markers such as the labyrinth zone (LZ) proportion within the placenta. This study aimed to investigate the impact of disrupted circadian rhythms on placental health and fetal development using animal models. Methods and resultsEmploying unstained photo-acoustic microscopy (PAM) and hematoxylin and eosin (HE)-stained images, we found them mutually reinforcing. Our images revealed the role of maternal circadian rhythm disrupted group (MCRD) on the LZ and fetus weight: a decrease in LZ area from 5.01 (4.25) mm2 HE (PAM) to 3.58 (2.62) mm2 HE (PAM) on day 16 and 6.48 (5.16) mm2 HE (PAM) to 4.61 (3.03) mm2 HE (PAM) on day 18, resulting in 0.71 times lower fetus weights. We have discriminated a decrease in the mean LZ to placenta area ratio from 64 % to 47 % on day 18 in mice with disrupted circadian rhythms with PAM. DiscussionThe study highlights the negative influence of circadian rhythm disruption on placental development and fetal well-being. Reduced LZ area and fetal weights in the MCRD group suggest compromised placental function under disrupted circadian rhythms. PAM imaging proved to be an efficient technique for assessing placental development, offering advantages over traditional staining methods. These findings contribute to understanding the underlying mechanisms of circadian disruption on reproductive health and fetal development. Further research is needed to explore interventions to mitigate these effects and improve pregnancy outcomes.

Disrupted mitochondrial response to nutrients is a presymptomatic event in the cortex of the APPSAA knock-in mouse model of Alzheimer's disease.

Reduced brain energy metabolism, mammalian target of rapamycin (mTOR) dysregulation, and extracellular amyloid beta (Aβ) oligomer (xcAβO) buildup are some well-known Alzheimer's disease (AD) features; how they promote neurodegeneration is poorly understood. We previously reported that xcAβOs inhibit nutrient-induced mitochondrial activity (NiMA) in cultured neurons. We now report NiMA disruption in vivo. Brain energy metabolism and oxygen consumption were recorded in heterozygous amyloid precursor protein knock-in (APPSAA) mice using two-photon fluorescence lifetime imaging and multiparametric photoacoustic microscopy. NiMA is inhibited in APPSAA mice before other defects are detected in these Aβ-producing animals that do not overexpress APP or contain foreign DNA inserts into genomic DNA. Glycogen synthase kinase 3 (GSK3β) signals through mTORC1 to regulate NiMA independently of mitochondrial biogenesis. Inhibition of GSK3β with TWS119 stimulates NiMA in cultured human neurons, and mitochondrial activity and oxygen consumption in APPSAA mice. NiMA disruption in vivo occurs before plaques, neuroinflammation, and cognitive decline in APPSAA mice, and may represent an early stage in human AD. Amyloid beta blocks communication between lysosomes and mitochondria in vivo. Nutrient-induced mitochondrial activity (NiMA) is disrupted long before the appearance of Alzheimer's disease (AD) histopathology in heterozygous amyloid precursor protein knock-in (APPSAA/+) mice. NiMA is disrupted long before learning and memory deficits in APPSAA/+ mice. Pharmacological interventions can rescue AD-related NiMA disruption in vivo.

Anti-interference photoacoustic microscopy with adaptive noise cancellation and echo recovery for in vivo ocular imaging

Anti-interference photoacoustic microscopy with adaptive noise cancellation and echo recovery for <i>in vivo</i> ocular imaging

High‐Speed Hemodynamic Imaging with Low‐Fluence Photoacoustic Microscopy and Self‐Supervised Single Volume Denoising

AbstractPhotoacoustic microscopy (PAM) enables label‐free imaging of the 3D vasculature and functional information with 2D lateral scan. The unique capacity in probing metabolism makes it ideal for animal research and clinical application. However, the high‐excitation power impedes the high‐speed monitoring of hemodynamics due to thermal accumulation and photon damage. To address this challenge, a self‐supervised photoacoustic single volume denoising (PSVD) approach, which combines 3D random sampling and noise augmentation to achieve 6 dB signal‐to‐noise‐ratio and contrast‐to‐noise‐ratio increases for the customized optical‐resolution photoacoustic microscope, is developed. Using PSVD, high‐quality PAM images of the mouse ear are acquired with only 10% fluence of normal excitation. Functional imaging is validated with this PSVD‐empowered low‐fluence PAM. Accurate oxygen saturation maps and high‐contrast flow kymographs are obtained. Moreover, the capability of this approach in the live mouse ear under hypercapnia is demonstrated. Further transformation into clinical imaging with low fluence will broaden the application of PAM.

All-fiber miniature non-contact photoacoustic probe based on photoacoustic remote sensing microscopy for vascular imaging in vivo.

Photoacoustic (PA) remote sensing (PARS) microscopy represents a significant advancement by eliminating the need for traditional acoustic coupling media in PA microscopy (PAM), thereby broadening its potential applications. However, current PARS microscopy setups predominantly rely on free-space optical components, which can be cumbersome to implement and limit the scope of imaging applications. In this study, we develop an all-fiber miniature non-contact PA probe based on PARS microscopy, utilizing a 532-nm excitation wavelength, and showcase its effectiveness in in vivo vascular imaging. Our approach integrates various fiber-optic components, including a wavelength division multiplexer, a mode field adaptor, a fiber lens, and an optical circulator, to streamline the implementation of the PARS microscopy system. Additionally, we have successfully developed a miniature PA probe with a diameter of 4 mm. The efficacy of our imaging setup is demonstrated through in vivo imaging of mouse brain vessels. By introducing this all-fiber miniature PA probe, our work may open up new opportunities for non-contact PAM applications.