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Significance: Photoacoustic microscopy (PAM) is a promising imaging technique to provide structural, functional, and molecular information for preclinical and clinical studies. However, expensive and bulky lasers and motorized stages have limited the broad applications of conventional PAM systems. A recent trend is to use low-cost light sources and miniaturized designs to develop a compact PAM system and expand its applications from benchtop to bedside. Aim: We provide (1) an overview of PAM systems and their limitations, (2) a comprehensive review of PAM systems with low-cost light sources and their applications, (3) a comprehensive review of PAM systems with miniaturized and handheld scanning designs, and (4) perspective applications and a summary of the cost-effective and miniaturized PAM systems. Approach: Papers published before July 2023 in the area of using low-cost light sources and miniaturized designs in PAM were reviewed. They were categorized into two main parts: (1) low-cost light sources and (2) miniaturized or handheld designs. The first part was classified into two subtypes: pulsed laser diode and continuous-wave laser diode. The second part was also classified into two subtypes: galvanometer scanner and micro-electro-mechanical system scanner. Results: Significant progress has been made in the development of PAM systems based on low-cost and compact light sources as well as miniaturized and handheld designs. Conclusions: The review highlights the potential of these advancements to revolutionize PAM technology, making it more accessible and practical for various applications in preclinical studies, clinical practice, and long-term monitoring. © 2023 The Authors.

Ultraviolet photoacoustic microscopy (UV-PAM) has been investigated to provide label-free and registration-free volumetric histological images for whole organs, offering new insights into complex biological organs. However, because of the high UV absorption of lipids and pigments in tissue, UV-PAM suffers from low image contrast and shallow image depth, hindering its capability for revealing various microstructures in organs. To improve the UV-PAM imaging contrast and imaging depth, here we propose to implement a state-of-the-art optical clearing technique, CUBIC (clear, unobstructed brain/body imaging cocktails and computational analysis), to wash out the lipids and pigments from tissues. Our results show that the UV-PAM imaging contrast and quality can be significantly improved after tissue clearing. With the cleared tissue, multilayers of cell nuclei can also be extracted from time-resolved PA signals. Tissue clearing-enhanced UV-PAM can provide fine details for organ imaging. © 2021 The Authors

Histological images can reveal rich cellular information of tissue sections, which are widely used by pathologists in disease diagnosis. However, the gold standard for histopathological examination is based on thin sections on slides, which involves inevitable time-consuming and labor-intensive tissue processing steps, hindering the possibility of intraoperative pathological assessment of the precious patient specimens. Here, by incorporating ultraviolet photoacoustic microscopy (UV-PAM) with deep learning, we show a rapid and label-free histological imaging method that can generate virtually stained histological images (termed Deep-PAM) for both thin sections and thick fresh tissue specimens. With the tissue non-destructive nature of UV-PAM, the imaged intact specimens can be reused for other ancillary tests. We demonstrated Deep-PAM on various tissue preparation protocols, including formalin-fixation and paraffin-embedding sections (7-µm thick) and frozen sections (7-µm thick) in traditional histology, and rapid assessment of intact fresh tissue (~ 2-mm thick, within 15 min for a tissue with a surface area of 5 mm × 5 mm). Deep-PAM potentially serves as a comprehensive histological imaging method that can be simultaneously applied in preoperative, intraoperative, and postoperative disease diagnosis. © 2021 The Authors

Ultraviolet photoacoustic microscopy (UV-PAM) has been investigated to provide label-free and registration-free volumetric histological images for whole organs, offering new insights into complex biological organs. However, because of the high UV absorption of lipids and pigments in tissue, UV-PAM suffers from low image contrast and shallow image depth, hindering its capability for revealing various microstructures in organs. To improve the UV-PAM imaging contrast and imaging depth, here we propose to implement a state-of-the-art optical clearing technique, CUBIC (clear, unobstructed brain/body imaging cocktails and computational analysis), to wash out the lipids and pigments from tissues. Our results show that the UV-PAM imaging contrast and quality can be significantly improved after tissue clearing. With the cleared tissue, multilayers of cell nuclei can also be extracted from time-resolved PA signals. Tissue clearing-enhanced UV-PAM can provide fine details for organ imaging. © 2021 The Authors

Histological images can reveal rich cellular information of tissue sections, which are widely used by pathologists in disease diagnosis. However, the gold standard for histopathological examination is based on thin sections on slides, which involves inevitable time-consuming and labor-intensive tissue processing steps, hindering the possibility of intraoperative pathological assessment of the precious patient specimens. Here, by incorporating ultraviolet photoacoustic microscopy (UV-PAM) with deep learning, we show a rapid and label-free histological imaging method that can generate virtually stained histological images (termed Deep-PAM) for both thin sections and thick fresh tissue specimens. With the tissue non-destructive nature of UV-PAM, the imaged intact specimens can be reused for other ancillary tests. We demonstrated Deep-PAM on various tissue preparation protocols, including formalin-fixation and paraffin-embedding sections (7-µm thick) and frozen sections (7-µm thick) in traditional histology, and rapid assessment of intact fresh tissue (~ 2-mm thick, within 15 min for a tissue with a surface area of 5 mm × 5 mm). Deep-PAM potentially serves as a comprehensive histological imaging method that can be simultaneously applied in preoperative, intraoperative, and postoperative disease diagnosis. © 2021 The Authors

The aim of this paper is to overcome the acoustic diffraction limit to achieve finer lateral resolution in and out of focus regions. For this purpose, a well-known structured-illumination method is used to increase the acoustic spatial bandwidth to improve the lateral resolution of the system. The illuminated optical beam is shaped by a digital micromirror device (DMD) to form sinusoidal patterns force to shift the object spatial spectrum. The shifted spectrum passes high spatial frequency components through the finite bandwidth of the system. Here, the phase compounding method is modified in comparison with [1] to increase the lateral resolution improvement from 2 to 5 times. To achieve this goal, adding the spatial frequency component of the second order to the fundamental component by considering phase shifts of 0,45,90 and 180 degree and orientations of 0,45,90, and 135 degree. The experimental results validate the performance of the system. © 2022 SPIE.

Ultraviolet photoacoustic microscopy (UV-PAM) has been investigated to provide label-free and registration-free volumetric histological images for whole organs, offering new insights into complex biological organs. However, because of the high UV absorption of lipids and pigments in tissue, UV-PAM suffers from low image contrast and shallow image depth, hindering its capability for revealing various microstructures in organs. To improve the UV-PAM imaging contrast and imaging depth, here we propose to implement a state-of-the-art optical clearing technique, CUBIC (clear, unobstructed brain/body imaging cocktails and computational analysis), to wash out the lipids and pigments from tissues. Our results show that the UV-PAM imaging contrast and quality can be significantly improved after tissue clearing. With the cleared tissue, multilayers of cell nuclei can also be extracted from time-resolved PA signals. Tissue clearing-enhanced UV-PAM can provide fine details for organ imaging. © 2021 The Authors

Histological images can reveal rich cellular information of tissue sections, which are widely used by pathologists in disease diagnosis. However, the gold standard for histopathological examination is based on thin sections on slides, which involves inevitable time-consuming and labor-intensive tissue processing steps, hindering the possibility of intraoperative pathological assessment of the precious patient specimens. Here, by incorporating ultraviolet photoacoustic microscopy (UV-PAM) with deep learning, we show a rapid and label-free histological imaging method that can generate virtually stained histological images (termed Deep-PAM) for both thin sections and thick fresh tissue specimens. With the tissue non-destructive nature of UV-PAM, the imaged intact specimens can be reused for other ancillary tests. We demonstrated Deep-PAM on various tissue preparation protocols, including formalin-fixation and paraffin-embedding sections (7-µm thick) and frozen sections (7-µm thick) in traditional histology, and rapid assessment of intact fresh tissue (~ 2-mm thick, within 15 min for a tissue with a surface area of 5 mm × 5 mm). Deep-PAM potentially serves as a comprehensive histological imaging method that can be simultaneously applied in preoperative, intraoperative, and postoperative disease diagnosis. © 2021 The Authors

[ES] La necesidad actual de seguir creando y mejorando técnicas de imagen para diagnóstico y pre- vención de enfermedades es el motor de miles de investigaciones en el sector de la biomedicina en todo el mundo. Este TFG se enmarca en la modalidad de imagen de microscopía fotoacústica de resolución óptica (OR-PAM). Esta reciente técnica de imagen, cuyo auge ha tenido lugar durante los últimos 15 años, permite obtener imagenes microscópicas de alta resolución tanto morfológicas como funcionales y cinéticas. Esto es debido a que los agentes de contraste utiliza- dos pueden ser tanto endógenos (hemoglobina, melanina, etc.) como exógenos (nanopartículas o tintes), resultando ser extremadamente útil y eficaz a la hora de detectar cánceres de piel y de mama, así como patologías vasculares en tejidos biológicos, dentro de un largo etcétera de potenciales aplicaciones de esta técnica de imagen. El objetivo de este TFG es el de desarrollar, caracterizar y analizar la validez de un nuevo sistema OR-PAM de bajo coste, utilizando fuentes de luz láser de menor calidad para abaratar su coste total. Para ello, se ha utilizado un diodo láser pulsado (PLD) como fuente de excitación fotoacústica, el cual se ha acoplado a una fibra óptica de núcleo cuadrado, con el objetivo de homogeneizar el patrón no uniforme que ofrece el PLD para conseguir una nueva fuente de luz cuadrada y uniforme. Utilizando una sonda de ultrasonidos phased-array de 128 canales, se han realizado varios tests de adquisición de imágenes fotoacústicas de un target de resolución de la USAF. La validación del sistema montado se ha realizado mediante mediciones de la energía de pulso y la sección transversal del haz en los puntos clave del sistema óptico, así como con la posterior implementación del algoritmo de reconstrucción de imagen de retardo y suma (DAS). También se han obtenido otros parámetros característicos como la resolución lateral, la relación señal a ruido (SNR) y el contraste de la imagen. Este proyecto, [EN] The current need to continue creating and improving imaging techniques for diagnosis and dis- ease prevention is the driving force behind thousands of research projects in the biomedical sector worldwide. This TFG is within the frame of optical-resolution photoacoustic microscopy imaging (OR-PAM). This recent imaging technique, which has been gaining interest over the last 15 years, allows to obtain high-resolution microscopic images of morphological, as well as functional and kinetical information. This is due to the fact that the used contrast agents can be both endogenous (haemoglobin, melanin, etc.) and exogenous (nanoparticles or dyes), which results extremely useful and effective when detecting skin and breast cancers, as well as vascu- lar pathologies in biological tissues, over a long list of future potential applications of this new imaging modality. The main objetive of this work is to develop, characterise and analyse the validity of a new low-cost OR-PAM system, using lower quality laser beam sources to reduce its total cost. To this purpose, a pulsed laser diode (PLD) was used as photoacoustic excitation source, which was coupled to a squared-core optical fiber, with the aim of homogenising the non-uniform light pattern offered by the PLD into a square and uniform laser spot. Using a 128-element phased- array ultrasound probe, several tests have been carried out to acquire photoacoustic images of a USAF resolution target. The validation of the assembled system was carried out by laser pulse energy and beam cross-section optical measurements at several key points of the system optics, as well as by the subsequent implementation of the delay-and-sum (DAS) image reconstruction algorithm. Also other PA imaging characteristic parameters such as the lateral resolution, the signal-to-noise ratio (SNR) and the image contrast were obtained. This work has included the preliminary study, the assembly and characterisation of the optical system, the development

[ES] La necesidad actual de seguir creando y mejorando técnicas de imagen para diagnóstico y pre- vención de enfermedades es el motor de miles de investigaciones en el sector de la biomedicina en todo el mundo. Este TFG se enmarca en la modalidad de imagen de microscopía fotoacústica de resolución óptica (OR-PAM). Esta reciente técnica de imagen, cuyo auge ha tenido lugar durante los últimos 15 años, permite obtener imagenes microscópicas de alta resolución tanto morfológicas como funcionales y cinéticas. Esto es debido a que los agentes de contraste utiliza- dos pueden ser tanto endógenos (hemoglobina, melanina, etc.) como exógenos (nanopartículas o tintes), resultando ser extremadamente útil y eficaz a la hora de detectar cánceres de piel y de mama, así como patologías vasculares en tejidos biológicos, dentro de un largo etcétera de potenciales aplicaciones de esta técnica de imagen. El objetivo de este TFG es el de desarrollar, caracterizar y analizar la validez de un nuevo sistema OR-PAM de bajo coste, utilizando fuentes de luz láser de menor calidad para abaratar su coste total. Para ello, se ha utilizado un diodo láser pulsado (PLD) como fuente de excitación fotoacústica, el cual se ha acoplado a una fibra óptica de núcleo cuadrado, con el objetivo de homogeneizar el patrón no uniforme que ofrece el PLD para conseguir una nueva fuente de luz cuadrada y uniforme. Utilizando una sonda de ultrasonidos phased-array de 128 canales, se han realizado varios tests de adquisición de imágenes fotoacústicas de un target de resolución de la USAF. La validación del sistema montado se ha realizado mediante mediciones de la energía de pulso y la sección transversal del haz en los puntos clave del sistema óptico, así como con la posterior implementación del algoritmo de reconstrucción de imagen de retardo y suma (DAS). También se han obtenido otros parámetros característicos como la resolución lateral, la relación señal a ruido (SNR) y el contraste de la imagen. Este proyecto, [EN] The current need to continue creating and improving imaging techniques for diagnosis and dis- ease prevention is the driving force behind thousands of research projects in the biomedical sector worldwide. This TFG is within the frame of optical-resolution photoacoustic microscopy imaging (OR-PAM). This recent imaging technique, which has been gaining interest over the last 15 years, allows to obtain high-resolution microscopic images of morphological, as well as functional and kinetical information. This is due to the fact that the used contrast agents can be both endogenous (haemoglobin, melanin, etc.) and exogenous (nanoparticles or dyes), which results extremely useful and effective when detecting skin and breast cancers, as well as vascu- lar pathologies in biological tissues, over a long list of future potential applications of this new imaging modality. The main objetive of this work is to develop, characterise and analyse the validity of a new low-cost OR-PAM system, using lower quality laser beam sources to reduce its total cost. To this purpose, a pulsed laser diode (PLD) was used as photoacoustic excitation source, which was coupled to a squared-core optical fiber, with the aim of homogenising the non-uniform light pattern offered by the PLD into a square and uniform laser spot. Using a 128-element phased- array ultrasound probe, several tests have been carried out to acquire photoacoustic images of a USAF resolution target. The validation of the assembled system was carried out by laser pulse energy and beam cross-section optical measurements at several key points of the system optics, as well as by the subsequent implementation of the delay-and-sum (DAS) image reconstruction algorithm. Also other PA imaging characteristic parameters such as the lateral resolution, the signal-to-noise ratio (SNR) and the image contrast were obtained. This work has included the preliminary study, the assembly and characterisation of the optical system, the development

[ES] La necesidad actual de seguir creando y mejorando técnicas de imagen para diagnóstico y pre- vención de enfermedades es el motor de miles de investigaciones en el sector de la biomedicina en todo el mundo. Este TFG se enmarca en la modalidad de imagen de microscopía fotoacústica de resolución óptica (OR-PAM). Esta reciente técnica de imagen, cuyo auge ha tenido lugar durante los últimos 15 años, permite obtener imagenes microscópicas de alta resolución tanto morfológicas como funcionales y cinéticas. Esto es debido a que los agentes de contraste utiliza- dos pueden ser tanto endógenos (hemoglobina, melanina, etc.) como exógenos (nanopartículas o tintes), resultando ser extremadamente útil y eficaz a la hora de detectar cánceres de piel y de mama, así como patologías vasculares en tejidos biológicos, dentro de un largo etcétera de potenciales aplicaciones de esta técnica de imagen. El objetivo de este TFG es el de desarrollar, caracterizar y analizar la validez de un nuevo sistema OR-PAM de bajo coste, utilizando fuentes de luz láser de menor calidad para abaratar su coste total. Para ello, se ha utilizado un diodo láser pulsado (PLD) como fuente de excitación fotoacústica, el cual se ha acoplado a una fibra óptica de núcleo cuadrado, con el objetivo de homogeneizar el patrón no uniforme que ofrece el PLD para conseguir una nueva fuente de luz cuadrada y uniforme. Utilizando una sonda de ultrasonidos phased-array de 128 canales, se han realizado varios tests de adquisición de imágenes fotoacústicas de un target de resolución de la USAF. La validación del sistema montado se ha realizado mediante mediciones de la energía de pulso y la sección transversal del haz en los puntos clave del sistema óptico, así como con la posterior implementación del algoritmo de reconstrucción de imagen de retardo y suma (DAS). También se han obtenido otros parámetros característicos como la resolución lateral, la relación señal a ruido (SNR) y el contraste de la imagen. Este proyecto, [EN] The current need to continue creating and improving imaging techniques for diagnosis and dis- ease prevention is the driving force behind thousands of research projects in the biomedical sector worldwide. This TFG is within the frame of optical-resolution photoacoustic microscopy imaging (OR-PAM). This recent imaging technique, which has been gaining interest over the last 15 years, allows to obtain high-resolution microscopic images of morphological, as well as functional and kinetical information. This is due to the fact that the used contrast agents can be both endogenous (haemoglobin, melanin, etc.) and exogenous (nanoparticles or dyes), which results extremely useful and effective when detecting skin and breast cancers, as well as vascu- lar pathologies in biological tissues, over a long list of future potential applications of this new imaging modality. The main objetive of this work is to develop, characterise and analyse the validity of a new low-cost OR-PAM system, using lower quality laser beam sources to reduce its total cost. To this purpose, a pulsed laser diode (PLD) was used as photoacoustic excitation source, which was coupled to a squared-core optical fiber, with the aim of homogenising the non-uniform light pattern offered by the PLD into a square and uniform laser spot. Using a 128-element phased- array ultrasound probe, several tests have been carried out to acquire photoacoustic images of a USAF resolution target. The validation of the assembled system was carried out by laser pulse energy and beam cross-section optical measurements at several key points of the system optics, as well as by the subsequent implementation of the delay-and-sum (DAS) image reconstruction algorithm. Also other PA imaging characteristic parameters such as the lateral resolution, the signal-to-noise ratio (SNR) and the image contrast were obtained. This work has included the preliminary study, the assembly and characterisation of the optical system, the development

We proposed a fast three-dimensional (3D) structured illumination photoacoustic microscopy (PAM). In the conventional PAM systems, the optical and acoustical beams need mechanical scanning to cover the whole area of interest for imaging imposing constraint on imaging speed. Using sinusoidal fringe illumination resulted in interference from a pair of tilted plane waves of different directions; capturing the resultant acoustic signal via a transducer array helped to improve lateral resolution and speed of the system while not degrading the depth-of-field (DOF). The sinusoidal structured illumination helps in more complete capture of spatial frequency components, which could be approved through a mathematical model of the system. Capturing more frequency components, in turn, results in improved frequency bandwidth and thus lateral resolution of the system. Simulation results show 5.4 dB improvements in image quality, based on the peak signal-to-noise ratio compared with a conventional structure. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

We proposed a fast three-dimensional (3D) structured illumination photoacoustic microscopy (PAM). In the conventional PAM systems, the optical and acoustical beams need mechanical scanning to cover the whole area of interest for imaging imposing constraint on imaging speed. Using sinusoidal fringe illumination resulted in interference from a pair of tilted plane waves of different directions; capturing the resultant acoustic signal via a transducer array helped to improve lateral resolution and speed of the system while not degrading the depth-of-field (DOF). The sinusoidal structured illumination helps in more complete capture of spatial frequency components, which could be approved through a mathematical model of the system. Capturing more frequency components, in turn, results in improved frequency bandwidth and thus lateral resolution of the system. Simulation results show 5.4 dB improvements in image quality, based on the peak signal-to-noise ratio compared with a conventional structure. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

Complex diseases, such as Alzheimer’s disease, are associated with sequences of changes in multiple disease-specific biomarkers. These biomarkers may show dynamic changes at specific stages of disease progression. Thus, testing/monitoring each biomarker may provide insight into specific disease-related processes, which can result in early diagnosis or even development of preventive measures. Obtaining a comprehensive information of biological tissues requires imaging of multiple optical contrasts, which is not typically offered by a single imaging modality. Thus, combining different contrast mechanisms to achieve simultaneous multimodal imaging is desirable. However, this process is highly challenging due to specific optical and hardware requirements for each optical imaging system. The objective of this dissertation is to develop a novel Penta-modal optical imaging system integrating photoacoustic microscopy (PAM), optical coherence tomography (OCT), optical Doppler tomography (ODT), OCT angiography (OCTA) and confocal fluorescence microscopy (CFM) in one platform providing comprehensive structural, functional, and molecular information of living biological tissues. The system can simultaneously image different biomarkers with a large field-of-view (FOV) and high-speed imaging. The large FOV and the high imaging speed is achieved by combining optical and mechanical scanning mechanisms. To compensate for an uneven surface of biological samples, which result in images with non-uniform resolution and low signal to noise ratio (SNR), we further develop a novel OCT-guided surface contour scanning methodology, a technique for adjusting objective lens focus to follow the contour of the sample surface, to provide a uniform spatial resolution and SNR across the region of interest (ROI). The imaging system was tested by imaging phantoms, ex vivo biological samples, and in vivo. The OCT-guided surface contour scanning methodology was utilized for imaging a leaf of purple quee

An estimated ∼250,000 new cases of both invasive and non-invasive breast cancer were diagnosed in US women almost every year. To reduce the local recurrence rate, the breast conserving surgery (BCS) is widely used as the initial therapy, which is to excise the tumor with a rim of normal surrounding tissue such that no cancer cells remain at the cut margin, Patients with positive margin commonly require a second surgical procedure to obtain clear margins. To this end, optical-resolution photoacoustic microscopy (OR-PAM) with ultraviolet (UV) laser illumination (OR-UV-PAM) has been developed for providing label-free, high-resolution, and histology like imaging of fixed, unprocessed breast tissue. To further improve the performance of OR-UV-PAM, here, we introduce dual-view UV-PAM (DV-UV-PAM) to significantly improve the axial resolution, achieving three-dimensional (3D) resolution isotropy. We first use 0.5 μm polystyrene beads and carbon fibers to validate the resolution isotropy improvement. Imaging of mouse brain slices further demonstrates the improved resolution isotropy, revealing the 3D structure of cell nuclei in detail, which facilitates quantitative cell nuclear analysis. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Rationale: Emerging evidence has suggested that sphingosine 1-phosphate (S1P), a bioactive metabolite of sphingolipids, may play an important role in the pathophysiological processes of cerebral hypoxia and ischemia. However, the influence of S1P on cerebral hemodynamics and metabolism remains unclear. Material and Methods: Uniquely capable of high-resolution, label-free, and comprehensive imaging of hemodynamics and oxygen metabolism in the mouse brain without the influence of general anesthesia, our newly developed head-restrained multi-parametric photoacoustic microscopy (PAM) is well suited for this mechanistic study. Here, combining the cutting-edge PAM and a selective inhibitor of sphingosine kinase 2 (SphK2) that can increase the blood S1P level, we investigated the role of S1P in cerebral oxygen supply-demand and its neuroprotective effects on global brain hypoxia induced by nitrogen gas inhalation and focal brain ischemia induced by transient middle cerebral artery occlusion (tMCAO). Results: Inhibition of SphK2, which increased the blood S1P, resulted in the elevation of both arterial and venous sO2 in the hypoxic mouse brain, while the cerebral blood flow remained unchanged. As a result, it gradually and significantly reduced the metabolic rate of oxygen. Furthermore, pre-treatment of the mice subject to tMCAO with the SphK2 inhibitor led to decreased infarct volume, improved motor function, and reduced neurological deficit, compared to the control treatment with a less potent R-enantiomer. In contrast, post-treatment with the inhibitor showed no improvement in the stroke outcomes. The failure for the post-treatment to induce neuroprotection was likely due to the relatively slow hemodynamic responses to the SphK2 inhibitor-evoked S1P intervention, which did not take effect before the brain injury was induced. Conclusions: Our results reveal that elevated blood S1P significantly changes cerebral hemodynamics and oxygen metabolism under hypoxia but not norm

Photoacoustic Microscopy (PAM) is a novel imaging technique that is commonly used with samples composed by soft tissue and that can provide penetration beyond the optical diffusion limit while maintaining high resolution. By using a short-pulsed laser to irradiate the tissue, part of the light energy is converted into heat, which induces the formation of acoustic waves that propagate inside the tissue and can be detected through ultrasound transducers. In this way, the absorption coefficient can be used as a contrast property of the matter, allowing the mapping of biological and chemical information. The essence of this master thesis is the design and start up of a PAM setup. This report contains the explanation of the different steps performed before reaching this goal, together with a justification of the different decisions that were taken along its construction. Finally, the resulting device and its main features are shown and discussed., Microscopia fotoacústica (PAM) és una nova tècnica d'imatge que és comunment utilitzada amb mostres composades per matèria tova i que pot aconseguir una penetració mes enllà del límit de difusió optica mantenint una alta resolució. Utilitzant un làser pulsat per a irradiar el teixit, part de la llum es converteix en calor, el qual indueix la formació d'ones acústiques que es propaguen per l'interior del teixit y que poden ser detectades mitjançant transductors. D'aquesta manera, el coeficient d'absorció pot ser utilitzat com a propietat de contrast de la matèria, permetent el mapeig de informació biològica i química. L'essència d'aquesta tesis de màster és el disseny i la posada a punt d'un montatge de PAM. Aquest informe conté l'explicació dels diferents passos realitzats abans d'aconseguir aquest objectiu, juntament amb la justificació de les diferents decisions que s'han pres durant la seva construcció. Finalment es mostren el dispositiu resultant i les seves principals característiques.

Optical coherence tomography (OCT) and Photoacoustic microscopy (PAM) are two noninvasive, high-resolution, three-dimensional, biomedical imaging modalities based on different contrast mechanisms. OCT detects the light backscattered from a biological sample either in the time or spectral domain using an interferometer to form an image. PAM is sensitive to optical absorption by detecting the light-induced acoustic waves to form an image. Due to their complementary contrast mechanisms, OCT and PAM are suitable for being combined to achieve multimodal imaging. In this dissertation, an optical coherence photoacoustic microscopy (OC-PAM) system was developed for in vivo multimodal retinal imaging with a pulsed broadband NIR light source. To test the capabilities of the system on multimodal ophthalmic imaging, the retina of pigmented rats was imaged. The OCT images showed the retinal structures with quality similar to conventional OCT, while the PAM images revealed the distribution of melanin in the retina since the NIR PAM signals are generated mainly from melanin in the posterior segment of the eye. By using the pulsed broadband light source, the OCT image quality highly depends on the pulse-to-pulse stability of the light source without averaging. In addition, laser safety is always a concern for in vivo applications, especially for eye imaging with a pulsed light source. Therefore, a continuous wave (CW) light source is desired for OC-PAM applications. An OC-PAM system using an intensity-modulated CW superluminescent diode was then developed. The system was tested for multimodal imaging the vasculature of a mouse ear in vivo by using Gold Nanorods (GNRs) as contrast agent for PAM, as well as excised porcine eyes ex vivo. Since the quantitative information of the optical properties extracted from the proposed NIR OC-PAM system is potentially able to provide a unique technique to evaluate the existence of melanin and lipofuscin specifically, a phantom study has been con

Clinical examination alone is not always sufficient to determine which burn wounds will heal spontaneously and which will require surgical intervention for optimal outcome. We present a review of optical modalities currently in clinical use and under development to assist burn surgeons in assessing burn wound severity, including conventional histology/light microscopy, laser Doppler imaging, indocyanine green videoangiography, near-infrared spectroscopy and spectral imaging, in vivo capillary microscopy, orthogonal polarization spectral imaging, reflectance-mode confocal microscopy, laser speckle imaging, spatial frequency domain imaging, photoacoustic microscopy, and polarization-sensitive optical coherence tomography.

Clinical examination alone is not always sufficient to determine which burn wounds will heal spontaneously and which will require surgical intervention for optimal outcome. We present a review of optical modalities currently in clinical use and under development to assist burn surgeons in assessing burn wound severity, including conventional histology/light microscopy, laser Doppler imaging, indocyanine green videoangiography, near-infrared spectroscopy and spectral imaging, in vivo capillary microscopy, orthogonal polarization spectral imaging, reflectance-mode confocal microscopy, laser speckle imaging, spatial frequency domain imaging, photoacoustic microscopy, and polarization-sensitive optical coherence tomography.

This is a brief introduction to the thermal wave principle with illustrations from ongoing work performed in connection with the photoacoustic microscopy laboratory at the U.S. Army Tank-Automotive Command. The photoacoustic or thermal wave technique offers a unique path for evaluation of the surface and near surface thermal properties and structure of a material. An example of one micron surface resolution will demonstrate the detail available. The variety of detection approaches will be illustrated with gas cell images; photoinductive images showing resolution 15 times better than achieved before with an eddy current imaging approach; and an image generated by an ion beam in which piezoelectric detection was used. The potential for quantifying the thickness and thermal properties of coatings will be demonstrated. Work in progress relating gas-cell images obtained with high laser intensity, which intentionally modified the surface, to subsequent x-ray measurement of residual stress will be presented.

This is a brief introduction to the thermal wave principle with illustrations from ongoing work performed in connection with the photoacoustic microscopy laboratory. The photoacoustic or thermal wave technique offers a unique path for evaluation of the surface and near surface thermal properties and structure of a material. An example of one micron surface resolution will demonstrate the detail available. The variety of detection approaches will be illustrated with gas-cell images; photoinductive images showing resolution 15 times better than achieved before with an eddy current imaging approach; and an image generated by an ion beam in which piezoelectric detection was used. The potential for quantifying the thickness and thermal properties of coatings will be demonstrated. Work in progress relating gas-cell images obtained with high laser intensity, which intentionally modified the surface, to subsequent x-ray measurement of residual stress will be presented.

Scanning Photoacoustic Microscopy (SPAM) images of aluminum with 0%, 24%, and 36% aluminum oxide grit, of surface roughness standards, and of track shoe pad rubber are shown. Considerable structure is evident in the images, even in the supposedly uniform sample of aluminum with 0% grit. Further research is necessary to relate the structure evident in the images which cannot be correlated with visible features to properties of the materials.

This report details the modifications to an existing ion implanter which were made in order to use it for ion acoustic microscopy. Results are described of tests of the technique on samples of cubic zirconia implanted with nitrogen ions. The utility of the technique for monitoring the progress of implantation in metals and ceramics is discussed. Keywords: Ion acoustic microscopy; photoacoustic microscopy; Thermal wave imaging; Zirconia; Ion Implantation.

The scanning photoacoustic microscope has been further developed and experimental results of thermal wave scattering from subsurface flaws have been compared with theoretical predictions. (Author)

The physics of the scanning photoacoustic microscopy (SPAM) has been developed. SPAM has been applied to NDE problems in high performance ceramics, and has been shown to be potentially useful for NDE in other solids, such as metals and semiconductors. One of the most important problems in nondestructive evaluation (NDE) has been that of detecting small (10 micron - 100 micron) flaws which lie just beneath the surface of an opaque solid. This problem is particularly acute for the technologically important, but brittle, ceramic materials, SiC and Si3N4. The objective of this program was to investigate and develop an entirely new NDE experimental technique, which we have named scanning photoacoustic microscopy (SPAM), and to test its applicability for subsurface NDE of ceramics.

The photoacoustic microscope is a device which uses a chopped laser beam as a modulated heat source and an acoustic cell and a detector to measure the microscopic thermal properties of materials. The result is a micrograph of the variations of the near surface thermal properties of the sample. As such it is a useful device for observing defects and the near subsurface grain structure of materials. Such structure is expected to be affected by nonsubstitutional impurities such as oxygen in titanium. We have applied this technique to the five samples of titaniumn alloy. The samples were first machined flat and polished to remove the disturbed surface region and tool marks which were present when they were received. Individual photoacoustic micrographs were taken of each sample and then comparative photoacoustic micrographs were taken of pairs of samples within the same cell to eliminate systematic errors due to variations of cell properties. These micrographs indicated small differences in the microscopic structures in the various samples but these differences appear to be overwhelmed by the gross variations in grain structure apparently induced by the rolling processes, etc. Rather large variations in structure were observed from point to point in the same sample, making it difficult to make meaningful comparison between samples. Micrographs which indicate the differences and similiarities of the samples will be presented. (Author), This article is from the Proceedings of the Workshop on Nondestructive Evaluation (NDE) of Titanium Alloys Held on 2-4 Feb 82 at the Naval Research Laboratory, Underwater Sound Reference Detachment, Orlando, FL., AD-A147 626, p113 - 124.

Considerable improvements have been achieved in the design of the photoacoustic microscope, including new sample cells, and better microcomputer hardware, firmware, and software for the scan control and data acquisition. The ND:YAG laser system has been made operational and has been used to obtain preliminary data in the development of a time-domain phtoacoustic microscope (pulse-echo themal wave imaging). Scan control instrumentation has been developed for this instrument, as well as electronics for data acquisition in the time domain. Theoretical calculations of pulsed thermal wave propagation and scattering have been carried out for comparison with experiment. Calculations for photoacoustic signals (cw) from model subsurface defects have been carried out and compared with experimental results. A key result is the theoretical prediction, and experimental verification that closed subsurface lateral cracks have a very characteristic photoacoustic phase signature which allows their discrimination form subsurface voids (or open cracks). Calculations have also been carried out for subsurface shpericl voids and tilted closed cracks. These calculations themselves were made possible because of our development of a very general theorem for SPAM using gas-filled cells, which greatly simplifies the theoretical calculations of the effects of thermal wave scattering from arbitrarily shaped flaws in solids.